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A novel frame shift mutation in the PQBP1 gene identified in a Tunisian family with X-linked mental retardation
European Journal of Medical Genetics 54 (2011) 241e246
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Original article
A novel frame shift mutation in the PQBP1 gene identified in a Tunisian family with X-linked mental retardation Imen Rejeb a, *, Lamia Ben Jemaa a, b, Leila Abaied a, Lilia Kraoua b, Yoann Saillour c, Faouzi Maazoul b, Jamel Chelly c, Habiba Chaabouni a, b a b c
Laboratoire de Génétique Humaine, Faculté de Médecine de Tunis, 15 Jebel Lakhdhar LaRabta, Tunis 1007, Tunisia Hôpital Charles Nicolle, Service des Maladies Héréditaires et Congénitales, Tunis, Tunisia Institut Cochin, Université Paris Descartes, Inserm U567, UMR 8104, Paris, France
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 September 2010 Accepted 20 January 2011 Available online 26 February 2011
Mental retardation (MR) is the most frequent cause of serious handicap in children and young adults. Despite recent progress, in most cases the molecular defects underlying this disorder remain unknown. Linkage studies followed by mutational analysis of known X-chromosomal genes related to mental retardation (MRX genes) localized within defined genetic intervals represent a rational strategy to identify a genetic cause of the disorder. Here, we report a Tunisian family including 3 males with severe to mild mental retardation, short stature, lean body and microcephaly; we mapped the disease to a unique interval encompassing Xp21.1eXq21.33 (with a maximum LOD score of 0.90). Subsequent mutation analysis of genes located in this interval allowed us to identify a truncating mutation in the PQBP1 gene. This mutation is an insertion of an adenosine residue in exon 5 (c.631insA). This frameshift insertion causes premature stop codon at amino acid position 226. The observed mutation was found in all males with MR in this family. Together with previously reported observations, our data further confirm that PQBP1 gene should be tested for males showing mental retardation, short stature, lean body and microcephaly. Ó 2011 Elsevier Masson SAS. All rights reserved.
Keywords: Lean body Mutation Microcephaly PQBP1 Short stature X-linked mental retardation
1. Introduction X-linked mental retardation (XLMR) is a common cause of monogenic intellectual disability affecting mostly males, partly accounting for the higher prevalence of mental retardation (MR) among males relative to females[1]. This prevalence is estimated to be 1 in 600 males and recent findings have shown that the proportion of MR caused by X-linked factors in men is 10e12% [2]. XLMR is classically divided into syndromic forms (MRXS) characterized by specific clinical, biochemical, or neurological features associated with mental retardation and non-syndromic forms (MRX) characterized by reduced mental capacities with no additional features. However, if we take into account recent molecular data, substantial overlaps between these two categories could be pointed out [3, 4]. Indeed, for several XLMR-related genes, mutations in the same gene are associated with both syndromic as well as non-syndromic XLMR forms. Mutations in the polyglutamine-
* Corresponding author. Tel.: þ216 24968503; fax: þ216 71570553. E-mail address: [email protected] (I. Rejeb). 1769-7212/$ e see front matter Ó 2011 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.ejmg.2011.01.010
binding protein 1 (PQBP1) supposed to interact with expanded polyglutamine tracts of huntingtin, ataxin, and androgen receptor [5e7] were found in patients with non-syndromic MR as well as in patients with syndromic MR and X-linked inheritance. In fact mutations in the PQBP1 gene located in Xp11.23 have been found in patients with Renpenning syndrome [8], Sutherland-Haan syndrome [7], Hamel cerebropalatocardiac syndrome [7], GolabiIto-Hall syndrome [9], Porteous syndrome [10], and MRX55 [7], as well as in other XLMR families. The PQBP1 gene comprises 6 exons that codes for a protein of 265 amino acids which contains several domains: a WW domain (characterized by two conserved tryptophans) encoded by the amino acid positions 47e78 that play an important role in the regulation of transcriptional activity by interacting with the carboxyl-terminal domain of the RNA polymerase II [11], a polyglutamine-binding region (in the polaramino-acid-rich domain: PRD) containing a DR/ER stretch which is encoded by exon 4 and involved in transcriptional control by binding to the polyQ region of the transcription factor Brn2 [6,12], a nuclear localization signal (NLS), and a C-terminal region shown to bind to a component of the nuclear pre-mRNA splicing machinery [13,14].
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So far, ten mutations identified in this gene were reported in 24 families: 3 small deletions [7,15e17], 2 missense mutation [9,16], 2 small insertions [7,15], and 3 gross deletions [18]. These mutations are resumed in Table 1. Recently Flynn et al. reported a 4.7 Mb duplication at Xp11.22ep11.23 of the PQBP1 gene leading to resembling Renpenning syndrome in a 47-year-old male [19]. However it is essential to note that the c. 334e354del (21 bp) was found in controls[18]. Therefore, the 21 bp in-frame deletions reported by Cossée et al. may be non-pathogenic, or alternatively could act subtly on PQBP1 function [18]. Here, we report the 11th mutation in this gene that was not previously reported. This insertion of one adenosine residue in exon 5 (c.631insA) is the second one located in the C-terminal region. This frameshift insertion causes premature stop codon at amino acid position 226. The observed mutation was found in 3 brothers with a phenotype comprising MR, short stature, lean body and microcephaly. 2. Methods 2.1. Case report We report a Tunisian family including 3 males with severe and mild mental retardation, short stature, lean body and microcephaly. Three mentally retarded males (II-1, II-2 and II-3), their mother (I-2) and their healthy brother (II-5) and sister (II-4) were available for this study (Fig. 1a). We reviewed their medical history and
performed personal interviews, clinical examination and molecular studies. Each patient had an uneventful pre- and perinatal history. The mother showed normal growth and mental function. For all patients, FRAXA and FRAXE mutations and large molecular rearrangements were excluded by conventional molecular approaches. Cytogenetic investigations, including high-resolution karyotype (700 band resolution), were also normal in all patients. 2.2. Molecular genetic studies On the basis of the pedigree of this family (Fig. 1a), we suspected an X-Linked mental retardation (XLMR) transmission. Blood samples were obtained after written consent from all tested individuals and/or tutors. Genomic DNA was extracted from peripheral blood lymphocytes using standard protocols for individuals I-2, II-1, II-2, II-3, II-4 and II-5. For genetic mapping, a total of 25 microsatellite markers distributed along the entire X chromosome were used. Lod scores for linkage between the disease locus and the genetic markers were calculated by the MLINK of the LINKAGE package (Lathrop and Laouel, 1984) (Fig. 1b). For PQBP1 gene analysis, the coding regions (six exons, GenBank accession number NM_005710) and flanking intronic sequences were amplified by PCR using genomic DNA. Primer sequences and PCR conditions can be obtained from authors upon request. PCR products were directly sequenced with the Big Dye Terminator ready reaction kit (PE Applied Biosystems) on an ABI-PRISM 3130 (PE Applied Biosystems). Base calling was
Table 1 Review of mutations reported in the PQBP1 gene, the protein domain they involve and a resume of the most common features. Syndrome/family
Mutation
Domain
Clinical features
References
Renpenning syndrome (original family) Renpenning syndrome (K8600) MRX55 N45
c.641ins C
C-terminal region
Lenski et al., [2004] [15]
c.459e462del AGAG
DR/ER repeat
c.459e462del AGAG c.459e462del AGAG
DR/ER repeat DR/ER repeat
Sheen family
c.459e462del AGAG
DR/ER repeat
P family
c.459e462del AGAG
DR/ER repeat
CB family
c.459e462del AGAG
DR/ER repeat
S family
c.459e462del AGAG
DR/ER repeat
B family
c.459e462del AGAG
DR/ER repeat
AH family
c.459e462del AGAG
DR/ER repeat
L family
c.586 C/T
NLS domain
Hamel cerebropalatocardiac (N40) Martinez-Garay family
c. 461e462 del AG
DR/ER repeat
c. 461e462 del AG
DR/ER repeat
Sutherland-Haan syndrome
c.463e464 dup AG
DR/ER repeat
Golabi-Ito-Hall
c.194 A/G
WW domain
Porteous syndrome N09 K9008
c.463e464 dup AG c.463e464 dup AG c.575e576 del AG
DR/ER repeat DR/ER repeat NLS domain
F1
c.547e569del(23bp)
F 2, F 3 and F 4 F5 Present study
c.334e354del (21bp) c.393e413del (21bp) c.631 ins A
After the DR/ ER repeat PRD domain PRD domain C-terminal region
MR, microcephaly, long face, short stature, lean body, small testes MR, microcephaly, long face, lean body, small testes MR, long face MR, microcephaly, long face, lean body, anal atresia MR, microcephaly, dysmorphic facies, hearing loss, short stature, periventricular heterotopia MR, microcephaly, dysmorphic facies, muscular atrophy lean body, MR, microcephaly, dysmorphic facies, muscular atrophy, lean body MR, microcephaly, dysmorphic facies, lean body MR, microcephaly, dysmorphic facies, muscular atrophy, lean body MR, microcephaly, dysmorphic facies, lean body MR, microcephaly, dysmorphic facies, muscular atrophy, lean body MR, microcephaly, short stature, long face, lean body, congenital heart defect MR, microcephaly, short stature, microphthalmia MR, microcephaly, short stature, long face, lean body, small testes, anal stenosis or atresia MR, microcephaly, short stature, triangular face, lean body, spastic diplegia MR, long face, lean body MR, microcephaly, long face, lean body MR, microcephaly, short stature long face, lean body MR, microcephaly, bilateral choanal atresia and anal atresia MR, behavioral anomalies MR, microcephaly, lower limbs spasticity MR, short stature, microcephaly, long face, lean body
Stevenson et al., [2005] [10] Kalscheuer et al., [2003] [7,27] Kalscheuer et al., [2003] [7] Sheen et al., [2010] [17] Germanaud et al., [2010] [16] Germanaud et al., [2010] [16] Germanaud et al., [2010] [16] Germanaud et al., [2010] [16] Germanaud et al., [2010] [16] Germanaud et al., [2010] [16] Kalscheuer et al., [2003] [7] Martinez-Garay et al., [2006] [23] Kalscheuer et al., [2003] [7] Lubs et al., [2006] [9] Stevenson et al., [2005] [10] Kalscheuer et al., [2003] [7] Lenski et al., [2004] [15] Cossée et al., [2006] [18] Cossée et al., [2006] [18] Cossée et al., [2006] [18] Present study
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a I
2
1
II 1 I-2
b
DXS1061 DXS1214 DXS8090 DXS8102 DXS8015 DXS8080 DXS8083 DXS1055 DXS1039 DXS1216 DXS1196 DXS1217 DXS8077 DXS1059 DXS8055
12 12 12 11 12 12 12 11 12 12 11 11 12 12 12
II-1 1 1 1 1 2 2 1 1 2 2 1 1 2 2 1
II-2 / 2 1 1 2 2 1 1 2 2 1 1 2 2 1
5
4
3
2 II-3
II-4
II-5
/ 2 1 1 2 2 1 1 2 2 1 1 2 2 1
13 13 22 11 11 11 12 11 11 12 12 12 11 13 12
1 1 2 1 1 1 2 1 1 1 1 1 1 2 1
Zmax -inf -inf 0.90 0.00 0.90 0.90 0.90 0.00 0.90 0.90 0.00 0.00 0.90 -inf -inf
c Ctrl
II-1
DR/ER repeat
d
PRD
N-terminal WW
C-terminal
NLS c. 641ins C c.631 ins A
c. 194 A→G
c. 586 C→T c. 575–576 del AG c. 547–569 del(23bp) c. 459–462 del AGAG c. 461–462 del AG c. 463–464 dup AG c.334-354del(21bp) c.393-413del(21bp)
Fig. 1. a. Pedigree of the family. Filled squares denote affected males and dotted circles denote carrier females. Asterisks indicate individuals for which DNA and phenotype data were available. b. Haplotypes of the Xp21.1-Xq21.33 region. Maximum Lod scores are indicated on the right. c. Sequence chromatograms of a control individual and the affected family member II.1 showing a partial sequence of exon 6 of PQBP1 gene. Dot indicates the nucleotidic variation c.631insA. d. Schematic representation of the protein structure of PQBP1 protein with positions of the functional domains (WW domain, PRD domain, NLS domain and C terminal region as well as the position of previously described mutations (c.194 A/G, c.334e354del(21bp), c.393e413del(21bp), c.459e462delAGAG, c.461e462delAG, c.463e464dupAG, c.547e569del(23bp), c.575e576delAG, c.586 C/T, c.641insC) and of the new c.631insA mutation describe in this report (underlined mutation).
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performed by using Sequencing analysis 5.2 software (Gene codes). Reference sequence was obtained from the UCSC Human Genome Browser (http://www.genom.ucsc.edu; PQBP1: NM_005710) and sequence analysis was performed by using SeqScape v2.5 (Applied Biosystems). 3. Results 3.1. Molecular genetic findings Segregation analysis using 25 polymorphic markers evenly distributed on the X chromosome allowed us to exclude implication in the MR phenotype of most regions of the X chromosome, except the region in Xp21.1eXq21.33 between the markers DXS8090 and DXS8077. At this region, affected male subjects were found to share a haplotype spanning about 58 Mb and the highest two-point Lod-score within the interval was 0.90 (Fig. 1b). This region contains more than 10 genes implicated in non-syndromic forms of XLMR. Because of phenotypic symptoms such as microcephaly and short stature and the significant overlap with reported phenotypes of patients with mutations in PQBP1 [17], we first screened the PQBP1 gene for mutations by direct sequencing of the
6 coding exons and their flanking intronic sequences (GenBank accession number. NM_005710). Mutation screening of the six exons of PQBP1 revealed an insertion of one adenosine residue in exon 5 (c.631insA). This mutation was reported neither in the literature, nor in online databases as polymorphism (Fig. 1c). This frameshift insertion causes premature stop codon at amino acid position 226. We analyzed the segregation of the mutation in the family and confirmed that the mutation segregates with the phenotype, in fact the observed mutation was found in all affected males and in their obligate carrier mother in this family. 3.2. Clinical features of the affected males The pedigree of the family is shown in Fig. 1a. Patient II.1 is a 30 year-old male with severe mental retardation and behavior disturbance. He was born by spontaneous delivery after an uneventful pregnancy. The neonatal period was normal. The birth weight was 2700 g. He experienced no significant childhood illness and had no seizures. The psychomotor development was normal. He was able to walk independently at the age of 1 year and did not have distinct
Fig. 2. Facial appearance of the 3 affected males. Photos of the affected males II-1, II-2, and II-3 showing the dysmorphic features. Note the slender posture of individuals II-2, and II-3.
I. Rejeb et al. / European Journal of Medical Genetics 54 (2011) 241e246
speech until the age of 3 years. He stopped normal school education at the age of 6 years because of attention deficiency. Currently, he works with his father in the farm. He is mentally retarded, with an apparent normal speech but difficulties in reading and writing. He is stubborn and talkative with slightly inarticulate speech with a nasal voice. He presented with microcephaly (occipitofrontal circumference OC ¼ 52 cm <3rd centile) short stature (158 cm <3rd centile) and lean body (49000 g < 3rd centile). He has normal tendon reflexes and no spasticity. Dysmorphic features were noticed with long face, high sloping forehead, large cupped ears, beaked nose, long columella, highly arched palate, rethrognathism and a central balding. He had a lean body with slender hands and feet (Fig. 2a). Patient II.2 is a 28 years old; he was born by spontaneous delivery after an uneventful pregnancy. The birth weight was 3000 g. In the neonatal period he experienced a fever episode at the age of 3 months. He experienced delayed motor and language milestones and attended special education throughout his school years. He was able to walk independently at the age of 2 years and did not have distinct speech until the age of 3 years. He performed poorly in a regular school setting. Clinical history showed mild mentally retarded boy with normal speech and nasal voice, he was able to write his name and write and read some numbers. He speaks unclearly and hastily and uses short sentences .His deep tendon reflexes are normal, there is no spasticity. He presented with microcephaly (OC ¼ 51 <3rd centile), short stature (158 cm <3rd centile), facial dysmorphism with long face, up slanting palpebral fissures, highly arched palate and a beginning of central balding. He had a lean body (46500 g <3rd centile) with slender hands and feet (Fig. 2b). He continues his education in a specialized school. Brain imaging with computerized tomography was normal for this patient. Patient II.3 is a 27 years old. He was born after normal pregnancy. The psychomotor development was normal according to his mother with walking at age of 1 year and initial speech at the age of 2 years. He required special education throughout school. Clinical examination showed microcephaly (OC ¼ 51 cm <3rd centile) short stature (161 cm <3rd centile) and a lean body (45000 g <3rd centile). He presented some dysmorphic features as up slanting palpebral fissures, narrow sloping forehead, large cupped ears, highly arched palate, beaked nose, rethrognathism and a beginning of central balding. He had a lean body with slender hands and feet (Fig. 2c) .He worked as a street sweeper of municipality. Additional clinical features are listed in Table 2.
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Table 2 Clinical features in the affected males. Patient and age
II.1 (30 years)
II.2 (28 years)
II.3 (27 years)
MR Height Head circumference Birth weight Weight Ear Ear length Forehead Eyes Inner Canthus Interpupillary Nose Mouth Palate Hand/Palm length Hair
Severe (IQ ¼ 40) 158.0 cm (<3rd) 52.0 cm (<3rd)
Mild (IQ ¼ 55) 158.0 cm (<3rd) 51.0 cm (<3rd)
Severe (IQ ¼ 40) 161.0 cm (<3rd), 51.0 cm (<3rd)
2700 g (10th) 49,000 g (<3rd) Protruding/Cupped 6 cm (50) High, sloping Normal 2.5 cm (<3rd) 5.5 cm (25e50) Beaked nose Normal Highly arched 17(25e50)/9 cm (3rd) Central balding
3500 g (>10th) 46,500 g (<3rd) Cupped 6.7 cm (70) High, sloping Normal 3 cm (50) 6 cm (>75) Beaked nose Thin lips Highly arched 18(50e75)/9 cm (3rd) Beginning of baldness Normal Short attention span, anxiety, clinging Poor and inarticulate Nasal
3000 g (>10th) 45,000 g (<3rd) Protruding/Cupped 6.5 cm (55) Narrow, sloping Normal 3 cm (50) 6 cm (>75) Beaked nose Normal Highly arched 17.5(50)/8 cm (<3rd) Beginning of baldness <10 ml Short attention span
Testicular size Behaviour and mental features Speech
Normal Short attention span, temper
Voice
Nasal
Inarticulate
Normal Nasal
the nuclear pre-mRNA splicing machinery [14]. A loss of functional C-terminal region might, therefore, contribute to the pathogenesis of MRXS in all the families. In fact the two mutations, this one and the one found in the family of Renpenning and colleagues lead to the same truncated protein (226 aminoacid), and are associated with phenotypes that share some common features specific to the Renpenning syndrome, such as mild to severe mental retardation, short stature, lean body build, upslanting palpebrae and microcephaly (detailed comparison is provided in Table 3). Though some divergent features could be pointed out (i.e. testicular volume that was normal in 2 of the affected males of our family, in fact only 1/3 presented with testicular volume below 10 ml Table 2). In addition, in our family severe mental retardation is noticed only in 2/3 of affected males their brother presented with mild mental retardation. These clinical findings highlight the relative inter- and intrafamilial phenotypic heterogeneity associated with mutations in PQBP1.
4. Discussion Our report describes the 24th family with mental retardation co-segregating with a mutation in the PQBP1 gene. This mutation is an insertion of one adenosine residue in exon 5 (c.631insA). This frameshift insertion causes a premature stop codon at amino acid position 226. This c.631insA mutation was detected in all affected males as well as in the obligate carrier mother, but was absent in the normal brother. Mutation described in this report is the second insertion mutation involving the C-terminal region. The first one was reported by Lenski et al. [15] in the family initially described by Renpenning and colleagues (1962) [8]. These two mutations cause a premature stop codon that can either lead to a truncated protein or to a functional null-allele owing to non sense mediated mRNA decay (NMD) [20]. A recent work of Musante et al. describes that in the patient with the c.641insC (p. Arg214fsX12) mutation in exon 5, the expected truncated product of 30 kDa was present [21]. All mutations identified so far in the PQBP1 gene lead to the disturbance or deletion of the C-terminal region in the protein. This domain has been shown to bind to U5-15 kDa [13] a component of
Table 3 Comparison of manifestations in our family and the original family of Renpenning [8].
Mutation Affected males Short stature (<3rd centile) Lean body build Microcephaly (<3rd centile) Upslanting palpebrae Large ears Cupped ears Short philtrum Small mouth Highly arched palate Central balding Small testes <10 ml
Renpenning et al. (1962) [8,15]
This report
c.641insC 20 6/10 3/4 13/14 4/4 1/10 0/5 5/5 0/5 0/5 3/5 4/9
c.631insA 3 3/3 3/3 3/3 3/3 3/3 3/3 0/3 0/3 3/3 1/3 1/3
Slow development/mental retardation Mild (IQ 50e70) 1/14 Severe (IQ <50) 13/14
1/3 3/3
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A recent work of Takahashi et al. [22] proposed that the nematode homologue of PQBP1 is involved in lipid metabolism of intestinal cells. Dysfunction of lipid metabolism might underlie lean body; in fact the majority of patients with PQBP1 mutation presented a slender posture and a lean body habitus. We propose that lean body must be added to the distinguishing features of PQBP1related syndrome especially for adult patients. Our data further confirm that PQBP1 gene should be tested for males showing mental retardation, short stature, lean body and microcephaly. Reported mutations in the PQBP1 involve all domains of the PQBP1 protein, and there is considerable inter- and intrafamilial phenotypic variation. Taking into account all mutations in the PQBP1gene that have been described, five groups of mutations can be classified according to the domain involved (see Table 1): missense mutation involving the WW domain [9], gross deletions involving the PRD domain [16], deletion or duplication of AG nucleotides affecting the DR/ER repeat in the PRD domain [7,10,23], deletion of AG nucleotides affecting the NLS domain [15] and small insertion involving the C-terminal region [15]. In fact Kalscheuer et al. [7] found three different frame shift mutations in the DR/ER repeat in the polar-aminoacid-rich domain (PRD) of the gene PQBP1 in five families including patients with Sutherlan-Haan syndrome [24] Hamel cerebropalatocardiac syndrome [25] and non-syndromic XLMR [26], the same mutations were found by Stevenson et al. as well as Martinez-Garay et al. [23], though reported phenotype was apparently different. However, as MR, microcephaly, short stature and lean habitus seem to be consistent findings among individuals with PQBP1 mutations, patients with these findings should be included in any tested scheme. 5. Conclusions In conclusion, our data further confirm that mentally retarded males with PQBP1 mutations share some common clinical symptoms. The emerging PQBP1-related phenotypes including mild to severe mental retardation, microcephaly, short stature, and lean body build. Therefore, mutation analysis of the PQBP1 gene is warranted for mentally retarded patients with this phenotype especially when family data are compatible with X-linked inheritance. Conflicts of interest The authors declare that they have no conflicts of interests. Acknowledgments We express our gratitude to the family for their active collaboration in the present study. References [1] R. Lehrke, Theory of X-linkage of major intellectual traits, Am. J. Ment. Defic. 76 (1972) 611e619. [2] H.H. Ropers, B.C. Hamel, X-linked mental retardation, Nat. Rev. Genet. 6 (2005) 46e57.
[3] S.G. Frints, G. Froyen, P. Marynen, J.P. Fryns, X-linked MR: vanishing boundaries between non-specific (MRX) and syndromic (MRXS) forms, Clin. Genet. 62 (2002) 423e432. [4] J. Chelly, J.L. Mandel, Monogenic causes of X-linked MR, Nat. Rev. Genet. 2 (2001) 669e680. [5] H. Okazawa, T. Rich, A. Chang, et al., Interaction between mutant ataxin-1 and PQBP-1 affects transcription and cell death, Neuron 34 (2002) 701e713. [6] M. Waragai, C.H. Lammers, S. Takeuchi, et al., PQBP-1, a novel polyglutamine tract binding protein, inhibits transcription activation by Brn-2 and affects cell survival, Hum. Mol. Genet. 8 (1999) 977e987. [7] V.M. Kalscheuer, K. Freude, L. Musante, et al., Mutations in the polyglutamine binding protein 1 gene cause X-linked mental retardation, Nat. Genet. 35 (2003) 313e315. [8] H. Renpenning, H.W. Gerrard, W.A. Zaleski, T. Tabata, Familial sexlinked mental retardation, Can. Med. Assoc. J. 87 (1962) 954e957. [9] H. Lubs, F.E. Abidi, R. Echeverri, et al., Golabi-Ito-Hall syndrome results from a missense mutation in the WW domain of the PQBP1 gene, J. Med. Genet. 43 (6) (2006 Jun) e30. [10] R.E. Stevenson, C.W. Bennett, F. Abidi, et al., Renpenning syndrome comes into focus, Am. J. Med. Genet. A. 134 (2005) 415e421. [11] M. Sudol, K. Sliwa, T. Russo, Functions of WW domains in the nucleus, FEBS Lett. 490 (2001) 190e195. [12] I. Imafuku, M. Waragai, S. Takeuchi, et al., Polar amino acid-rich sequences bind to polyglutamine tracts, Biochem. Biophys. Res. Commun. 25 (1998) 16e20. [13] M. Waragai, E. Junn, M. Kajikawa, et al., PQBP-1/Npw38, a nuclear protein binding to the polyglutamine tract, interacts with U5-15 kD/dim1p via the carboxyl-terminal domain, Biochem. Biophys. Res. Commun. 273 (2000) 592e595. [14] K. Reuter, S. Nottrott, P. Fabrizio, R. Lührmann, R. Ficner, Identification, characterization and crystal structure analysis of the human spliceosomal U5 snRNP-specific 15 kD protein, J. Mol. Biol. 294 (1999) 515e525. [15] C. Lenski, F. Abidi, A. Meindl, et al., Novel truncating mutations in the polyglutamine tract binding protein 1 gene (PQBP1) cause Renpenning syndrome and X-linked mental retardation in another family with microcephaly, Am. J. Hum. Genet. 74 (2004) 777e780. [16] D. Germanaud, M. Rossi, G. Bussy, et al., The Renpenning syndrome spectrum: new clinical insights supported by 13 new PQBP1-mutated males, Clin. Genet. (2010 Sep 20). [17] V.L. Sheen, A.R. Torres, X. Du, et al., Mutation in PQBP1 is associated with periventricular heterotopia, Am. J. Med. Genet. A. 152A (11) (2010 Nov) 2888e2890. [18] M. Cossée, B. Demeer, P. Blanchet, et al., Exonic microdeletions in the X-linked PQBP1 gene in mentally retarded patients: a pathogenic mutation and inframe deletions of uncertain effect, Eur. J. Hum. Genet. 14 (2006) 418e425. [19] M. Flynn, Y.S. Zou, A. Milunsky, Whole gene duplication of the PQBP1 gene in syndrome resembling Renpenning, Am. J. Med. Genet. A 155 (1) (2011 Jan) 141e144. [20] F. Lejeune, L.E. Maquat, Mechanistic links between nonsense mediated mRNA decay and pre-mRNA splicing in mammalian cells, Curr. Opin. Cell Biol. 17 (2005) 309e315. [21] L. Musante, S.A. Kunde, T.O. Sulistio, et al., Common pathological mutations in PQBP1 induce nonsense-mediated mRNA decay and enhance exclusion of the mutant exon, Hum. Mutat. 31 (1) (2010 Jan) 90e98. [22] K. Takahashi, S. Yoshina, M. Masashi, et al., Nematode homologue of PQBP1, a mental retardation causative gene, is involved in lipid metabolism, PLoS ONE 4 (1) (2009) e4104. [23] I. Martínez-Garay, M. Tomás, S. Oltra, et al., A two base pair deletion in the PQBP1 gene is associated with microphthalmia, microcephaly, and mental retardation, Eur. J. Hum. Genet. 15 (2007) 29e34. [24] G.R. Sutherland, A.K. Gedeon, E.A. Haan, P. Woodroffe, J.C. Mulley, Linkage studies with the gene for an Xelinked syndrome of mental retardation, microcephaly and spastic diplegia (MRX2), Am. J. Med. Genet. 30 (1988) 493e508. [25] T. Kleefstra, C.E. Franken, Y.H. Arens, et al., Genotype phenotype studies in three families with mutations in the polyglutamine-binding protein 1 gene (PQBP1), Clin. Genet. 66 (2004) 318e326. [26] M. Golabi, M. Ito, B.D. Hall, A new X-linked multiple congenital anomalies/ mental retardation syndrome, Am. J. Med. Genet. 17 (1984) 367e374. [27] S.C. Deqaqi, M. N’Guessan, J. Forner, et al., A gene for non-specific X-linked mental retardation (MRX55) is located in Xp11, Ann. Genet. 41 (1998) 11e16.
Contents lists available at ScienceDirect
European Journal of Medical Genetics journal homepage: http://www.elsevier.com/locate/ejmg
Original article
A novel frame shift mutation in the PQBP1 gene identified in a Tunisian family with X-linked mental retardation Imen Rejeb a, *, Lamia Ben Jemaa a, b, Leila Abaied a, Lilia Kraoua b, Yoann Saillour c, Faouzi Maazoul b, Jamel Chelly c, Habiba Chaabouni a, b a b c
Laboratoire de Génétique Humaine, Faculté de Médecine de Tunis, 15 Jebel Lakhdhar LaRabta, Tunis 1007, Tunisia Hôpital Charles Nicolle, Service des Maladies Héréditaires et Congénitales, Tunis, Tunisia Institut Cochin, Université Paris Descartes, Inserm U567, UMR 8104, Paris, France
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 September 2010 Accepted 20 January 2011 Available online 26 February 2011
Mental retardation (MR) is the most frequent cause of serious handicap in children and young adults. Despite recent progress, in most cases the molecular defects underlying this disorder remain unknown. Linkage studies followed by mutational analysis of known X-chromosomal genes related to mental retardation (MRX genes) localized within defined genetic intervals represent a rational strategy to identify a genetic cause of the disorder. Here, we report a Tunisian family including 3 males with severe to mild mental retardation, short stature, lean body and microcephaly; we mapped the disease to a unique interval encompassing Xp21.1eXq21.33 (with a maximum LOD score of 0.90). Subsequent mutation analysis of genes located in this interval allowed us to identify a truncating mutation in the PQBP1 gene. This mutation is an insertion of an adenosine residue in exon 5 (c.631insA). This frameshift insertion causes premature stop codon at amino acid position 226. The observed mutation was found in all males with MR in this family. Together with previously reported observations, our data further confirm that PQBP1 gene should be tested for males showing mental retardation, short stature, lean body and microcephaly. Ó 2011 Elsevier Masson SAS. All rights reserved.
Keywords: Lean body Mutation Microcephaly PQBP1 Short stature X-linked mental retardation
1. Introduction X-linked mental retardation (XLMR) is a common cause of monogenic intellectual disability affecting mostly males, partly accounting for the higher prevalence of mental retardation (MR) among males relative to females[1]. This prevalence is estimated to be 1 in 600 males and recent findings have shown that the proportion of MR caused by X-linked factors in men is 10e12% [2]. XLMR is classically divided into syndromic forms (MRXS) characterized by specific clinical, biochemical, or neurological features associated with mental retardation and non-syndromic forms (MRX) characterized by reduced mental capacities with no additional features. However, if we take into account recent molecular data, substantial overlaps between these two categories could be pointed out [3, 4]. Indeed, for several XLMR-related genes, mutations in the same gene are associated with both syndromic as well as non-syndromic XLMR forms. Mutations in the polyglutamine-
* Corresponding author. Tel.: þ216 24968503; fax: þ216 71570553. E-mail address: [email protected] (I. Rejeb). 1769-7212/$ e see front matter Ó 2011 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.ejmg.2011.01.010
binding protein 1 (PQBP1) supposed to interact with expanded polyglutamine tracts of huntingtin, ataxin, and androgen receptor [5e7] were found in patients with non-syndromic MR as well as in patients with syndromic MR and X-linked inheritance. In fact mutations in the PQBP1 gene located in Xp11.23 have been found in patients with Renpenning syndrome [8], Sutherland-Haan syndrome [7], Hamel cerebropalatocardiac syndrome [7], GolabiIto-Hall syndrome [9], Porteous syndrome [10], and MRX55 [7], as well as in other XLMR families. The PQBP1 gene comprises 6 exons that codes for a protein of 265 amino acids which contains several domains: a WW domain (characterized by two conserved tryptophans) encoded by the amino acid positions 47e78 that play an important role in the regulation of transcriptional activity by interacting with the carboxyl-terminal domain of the RNA polymerase II [11], a polyglutamine-binding region (in the polaramino-acid-rich domain: PRD) containing a DR/ER stretch which is encoded by exon 4 and involved in transcriptional control by binding to the polyQ region of the transcription factor Brn2 [6,12], a nuclear localization signal (NLS), and a C-terminal region shown to bind to a component of the nuclear pre-mRNA splicing machinery [13,14].
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So far, ten mutations identified in this gene were reported in 24 families: 3 small deletions [7,15e17], 2 missense mutation [9,16], 2 small insertions [7,15], and 3 gross deletions [18]. These mutations are resumed in Table 1. Recently Flynn et al. reported a 4.7 Mb duplication at Xp11.22ep11.23 of the PQBP1 gene leading to resembling Renpenning syndrome in a 47-year-old male [19]. However it is essential to note that the c. 334e354del (21 bp) was found in controls[18]. Therefore, the 21 bp in-frame deletions reported by Cossée et al. may be non-pathogenic, or alternatively could act subtly on PQBP1 function [18]. Here, we report the 11th mutation in this gene that was not previously reported. This insertion of one adenosine residue in exon 5 (c.631insA) is the second one located in the C-terminal region. This frameshift insertion causes premature stop codon at amino acid position 226. The observed mutation was found in 3 brothers with a phenotype comprising MR, short stature, lean body and microcephaly. 2. Methods 2.1. Case report We report a Tunisian family including 3 males with severe and mild mental retardation, short stature, lean body and microcephaly. Three mentally retarded males (II-1, II-2 and II-3), their mother (I-2) and their healthy brother (II-5) and sister (II-4) were available for this study (Fig. 1a). We reviewed their medical history and
performed personal interviews, clinical examination and molecular studies. Each patient had an uneventful pre- and perinatal history. The mother showed normal growth and mental function. For all patients, FRAXA and FRAXE mutations and large molecular rearrangements were excluded by conventional molecular approaches. Cytogenetic investigations, including high-resolution karyotype (700 band resolution), were also normal in all patients. 2.2. Molecular genetic studies On the basis of the pedigree of this family (Fig. 1a), we suspected an X-Linked mental retardation (XLMR) transmission. Blood samples were obtained after written consent from all tested individuals and/or tutors. Genomic DNA was extracted from peripheral blood lymphocytes using standard protocols for individuals I-2, II-1, II-2, II-3, II-4 and II-5. For genetic mapping, a total of 25 microsatellite markers distributed along the entire X chromosome were used. Lod scores for linkage between the disease locus and the genetic markers were calculated by the MLINK of the LINKAGE package (Lathrop and Laouel, 1984) (Fig. 1b). For PQBP1 gene analysis, the coding regions (six exons, GenBank accession number NM_005710) and flanking intronic sequences were amplified by PCR using genomic DNA. Primer sequences and PCR conditions can be obtained from authors upon request. PCR products were directly sequenced with the Big Dye Terminator ready reaction kit (PE Applied Biosystems) on an ABI-PRISM 3130 (PE Applied Biosystems). Base calling was
Table 1 Review of mutations reported in the PQBP1 gene, the protein domain they involve and a resume of the most common features. Syndrome/family
Mutation
Domain
Clinical features
References
Renpenning syndrome (original family) Renpenning syndrome (K8600) MRX55 N45
c.641ins C
C-terminal region
Lenski et al., [2004] [15]
c.459e462del AGAG
DR/ER repeat
c.459e462del AGAG c.459e462del AGAG
DR/ER repeat DR/ER repeat
Sheen family
c.459e462del AGAG
DR/ER repeat
P family
c.459e462del AGAG
DR/ER repeat
CB family
c.459e462del AGAG
DR/ER repeat
S family
c.459e462del AGAG
DR/ER repeat
B family
c.459e462del AGAG
DR/ER repeat
AH family
c.459e462del AGAG
DR/ER repeat
L family
c.586 C/T
NLS domain
Hamel cerebropalatocardiac (N40) Martinez-Garay family
c. 461e462 del AG
DR/ER repeat
c. 461e462 del AG
DR/ER repeat
Sutherland-Haan syndrome
c.463e464 dup AG
DR/ER repeat
Golabi-Ito-Hall
c.194 A/G
WW domain
Porteous syndrome N09 K9008
c.463e464 dup AG c.463e464 dup AG c.575e576 del AG
DR/ER repeat DR/ER repeat NLS domain
F1
c.547e569del(23bp)
F 2, F 3 and F 4 F5 Present study
c.334e354del (21bp) c.393e413del (21bp) c.631 ins A
After the DR/ ER repeat PRD domain PRD domain C-terminal region
MR, microcephaly, long face, short stature, lean body, small testes MR, microcephaly, long face, lean body, small testes MR, long face MR, microcephaly, long face, lean body, anal atresia MR, microcephaly, dysmorphic facies, hearing loss, short stature, periventricular heterotopia MR, microcephaly, dysmorphic facies, muscular atrophy lean body, MR, microcephaly, dysmorphic facies, muscular atrophy, lean body MR, microcephaly, dysmorphic facies, lean body MR, microcephaly, dysmorphic facies, muscular atrophy, lean body MR, microcephaly, dysmorphic facies, lean body MR, microcephaly, dysmorphic facies, muscular atrophy, lean body MR, microcephaly, short stature, long face, lean body, congenital heart defect MR, microcephaly, short stature, microphthalmia MR, microcephaly, short stature, long face, lean body, small testes, anal stenosis or atresia MR, microcephaly, short stature, triangular face, lean body, spastic diplegia MR, long face, lean body MR, microcephaly, long face, lean body MR, microcephaly, short stature long face, lean body MR, microcephaly, bilateral choanal atresia and anal atresia MR, behavioral anomalies MR, microcephaly, lower limbs spasticity MR, short stature, microcephaly, long face, lean body
Stevenson et al., [2005] [10] Kalscheuer et al., [2003] [7,27] Kalscheuer et al., [2003] [7] Sheen et al., [2010] [17] Germanaud et al., [2010] [16] Germanaud et al., [2010] [16] Germanaud et al., [2010] [16] Germanaud et al., [2010] [16] Germanaud et al., [2010] [16] Germanaud et al., [2010] [16] Kalscheuer et al., [2003] [7] Martinez-Garay et al., [2006] [23] Kalscheuer et al., [2003] [7] Lubs et al., [2006] [9] Stevenson et al., [2005] [10] Kalscheuer et al., [2003] [7] Lenski et al., [2004] [15] Cossée et al., [2006] [18] Cossée et al., [2006] [18] Cossée et al., [2006] [18] Present study
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243
a I
2
1
II 1 I-2
b
DXS1061 DXS1214 DXS8090 DXS8102 DXS8015 DXS8080 DXS8083 DXS1055 DXS1039 DXS1216 DXS1196 DXS1217 DXS8077 DXS1059 DXS8055
12 12 12 11 12 12 12 11 12 12 11 11 12 12 12
II-1 1 1 1 1 2 2 1 1 2 2 1 1 2 2 1
II-2 / 2 1 1 2 2 1 1 2 2 1 1 2 2 1
5
4
3
2 II-3
II-4
II-5
/ 2 1 1 2 2 1 1 2 2 1 1 2 2 1
13 13 22 11 11 11 12 11 11 12 12 12 11 13 12
1 1 2 1 1 1 2 1 1 1 1 1 1 2 1
Zmax -inf -inf 0.90 0.00 0.90 0.90 0.90 0.00 0.90 0.90 0.00 0.00 0.90 -inf -inf
c Ctrl
II-1
DR/ER repeat
d
PRD
N-terminal WW
C-terminal
NLS c. 641ins C c.631 ins A
c. 194 A→G
c. 586 C→T c. 575–576 del AG c. 547–569 del(23bp) c. 459–462 del AGAG c. 461–462 del AG c. 463–464 dup AG c.334-354del(21bp) c.393-413del(21bp)
Fig. 1. a. Pedigree of the family. Filled squares denote affected males and dotted circles denote carrier females. Asterisks indicate individuals for which DNA and phenotype data were available. b. Haplotypes of the Xp21.1-Xq21.33 region. Maximum Lod scores are indicated on the right. c. Sequence chromatograms of a control individual and the affected family member II.1 showing a partial sequence of exon 6 of PQBP1 gene. Dot indicates the nucleotidic variation c.631insA. d. Schematic representation of the protein structure of PQBP1 protein with positions of the functional domains (WW domain, PRD domain, NLS domain and C terminal region as well as the position of previously described mutations (c.194 A/G, c.334e354del(21bp), c.393e413del(21bp), c.459e462delAGAG, c.461e462delAG, c.463e464dupAG, c.547e569del(23bp), c.575e576delAG, c.586 C/T, c.641insC) and of the new c.631insA mutation describe in this report (underlined mutation).
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performed by using Sequencing analysis 5.2 software (Gene codes). Reference sequence was obtained from the UCSC Human Genome Browser (http://www.genom.ucsc.edu; PQBP1: NM_005710) and sequence analysis was performed by using SeqScape v2.5 (Applied Biosystems). 3. Results 3.1. Molecular genetic findings Segregation analysis using 25 polymorphic markers evenly distributed on the X chromosome allowed us to exclude implication in the MR phenotype of most regions of the X chromosome, except the region in Xp21.1eXq21.33 between the markers DXS8090 and DXS8077. At this region, affected male subjects were found to share a haplotype spanning about 58 Mb and the highest two-point Lod-score within the interval was 0.90 (Fig. 1b). This region contains more than 10 genes implicated in non-syndromic forms of XLMR. Because of phenotypic symptoms such as microcephaly and short stature and the significant overlap with reported phenotypes of patients with mutations in PQBP1 [17], we first screened the PQBP1 gene for mutations by direct sequencing of the
6 coding exons and their flanking intronic sequences (GenBank accession number. NM_005710). Mutation screening of the six exons of PQBP1 revealed an insertion of one adenosine residue in exon 5 (c.631insA). This mutation was reported neither in the literature, nor in online databases as polymorphism (Fig. 1c). This frameshift insertion causes premature stop codon at amino acid position 226. We analyzed the segregation of the mutation in the family and confirmed that the mutation segregates with the phenotype, in fact the observed mutation was found in all affected males and in their obligate carrier mother in this family. 3.2. Clinical features of the affected males The pedigree of the family is shown in Fig. 1a. Patient II.1 is a 30 year-old male with severe mental retardation and behavior disturbance. He was born by spontaneous delivery after an uneventful pregnancy. The neonatal period was normal. The birth weight was 2700 g. He experienced no significant childhood illness and had no seizures. The psychomotor development was normal. He was able to walk independently at the age of 1 year and did not have distinct
Fig. 2. Facial appearance of the 3 affected males. Photos of the affected males II-1, II-2, and II-3 showing the dysmorphic features. Note the slender posture of individuals II-2, and II-3.
I. Rejeb et al. / European Journal of Medical Genetics 54 (2011) 241e246
speech until the age of 3 years. He stopped normal school education at the age of 6 years because of attention deficiency. Currently, he works with his father in the farm. He is mentally retarded, with an apparent normal speech but difficulties in reading and writing. He is stubborn and talkative with slightly inarticulate speech with a nasal voice. He presented with microcephaly (occipitofrontal circumference OC ¼ 52 cm <3rd centile) short stature (158 cm <3rd centile) and lean body (49000 g < 3rd centile). He has normal tendon reflexes and no spasticity. Dysmorphic features were noticed with long face, high sloping forehead, large cupped ears, beaked nose, long columella, highly arched palate, rethrognathism and a central balding. He had a lean body with slender hands and feet (Fig. 2a). Patient II.2 is a 28 years old; he was born by spontaneous delivery after an uneventful pregnancy. The birth weight was 3000 g. In the neonatal period he experienced a fever episode at the age of 3 months. He experienced delayed motor and language milestones and attended special education throughout his school years. He was able to walk independently at the age of 2 years and did not have distinct speech until the age of 3 years. He performed poorly in a regular school setting. Clinical history showed mild mentally retarded boy with normal speech and nasal voice, he was able to write his name and write and read some numbers. He speaks unclearly and hastily and uses short sentences .His deep tendon reflexes are normal, there is no spasticity. He presented with microcephaly (OC ¼ 51 <3rd centile), short stature (158 cm <3rd centile), facial dysmorphism with long face, up slanting palpebral fissures, highly arched palate and a beginning of central balding. He had a lean body (46500 g <3rd centile) with slender hands and feet (Fig. 2b). He continues his education in a specialized school. Brain imaging with computerized tomography was normal for this patient. Patient II.3 is a 27 years old. He was born after normal pregnancy. The psychomotor development was normal according to his mother with walking at age of 1 year and initial speech at the age of 2 years. He required special education throughout school. Clinical examination showed microcephaly (OC ¼ 51 cm <3rd centile) short stature (161 cm <3rd centile) and a lean body (45000 g <3rd centile). He presented some dysmorphic features as up slanting palpebral fissures, narrow sloping forehead, large cupped ears, highly arched palate, beaked nose, rethrognathism and a beginning of central balding. He had a lean body with slender hands and feet (Fig. 2c) .He worked as a street sweeper of municipality. Additional clinical features are listed in Table 2.
245
Table 2 Clinical features in the affected males. Patient and age
II.1 (30 years)
II.2 (28 years)
II.3 (27 years)
MR Height Head circumference Birth weight Weight Ear Ear length Forehead Eyes Inner Canthus Interpupillary Nose Mouth Palate Hand/Palm length Hair
Severe (IQ ¼ 40) 158.0 cm (<3rd) 52.0 cm (<3rd)
Mild (IQ ¼ 55) 158.0 cm (<3rd) 51.0 cm (<3rd)
Severe (IQ ¼ 40) 161.0 cm (<3rd), 51.0 cm (<3rd)
2700 g (10th) 49,000 g (<3rd) Protruding/Cupped 6 cm (50) High, sloping Normal 2.5 cm (<3rd) 5.5 cm (25e50) Beaked nose Normal Highly arched 17(25e50)/9 cm (3rd) Central balding
3500 g (>10th) 46,500 g (<3rd) Cupped 6.7 cm (70) High, sloping Normal 3 cm (50) 6 cm (>75) Beaked nose Thin lips Highly arched 18(50e75)/9 cm (3rd) Beginning of baldness Normal Short attention span, anxiety, clinging Poor and inarticulate Nasal
3000 g (>10th) 45,000 g (<3rd) Protruding/Cupped 6.5 cm (55) Narrow, sloping Normal 3 cm (50) 6 cm (>75) Beaked nose Normal Highly arched 17.5(50)/8 cm (<3rd) Beginning of baldness <10 ml Short attention span
Testicular size Behaviour and mental features Speech
Normal Short attention span, temper
Voice
Nasal
Inarticulate
Normal Nasal
the nuclear pre-mRNA splicing machinery [14]. A loss of functional C-terminal region might, therefore, contribute to the pathogenesis of MRXS in all the families. In fact the two mutations, this one and the one found in the family of Renpenning and colleagues lead to the same truncated protein (226 aminoacid), and are associated with phenotypes that share some common features specific to the Renpenning syndrome, such as mild to severe mental retardation, short stature, lean body build, upslanting palpebrae and microcephaly (detailed comparison is provided in Table 3). Though some divergent features could be pointed out (i.e. testicular volume that was normal in 2 of the affected males of our family, in fact only 1/3 presented with testicular volume below 10 ml Table 2). In addition, in our family severe mental retardation is noticed only in 2/3 of affected males their brother presented with mild mental retardation. These clinical findings highlight the relative inter- and intrafamilial phenotypic heterogeneity associated with mutations in PQBP1.
4. Discussion Our report describes the 24th family with mental retardation co-segregating with a mutation in the PQBP1 gene. This mutation is an insertion of one adenosine residue in exon 5 (c.631insA). This frameshift insertion causes a premature stop codon at amino acid position 226. This c.631insA mutation was detected in all affected males as well as in the obligate carrier mother, but was absent in the normal brother. Mutation described in this report is the second insertion mutation involving the C-terminal region. The first one was reported by Lenski et al. [15] in the family initially described by Renpenning and colleagues (1962) [8]. These two mutations cause a premature stop codon that can either lead to a truncated protein or to a functional null-allele owing to non sense mediated mRNA decay (NMD) [20]. A recent work of Musante et al. describes that in the patient with the c.641insC (p. Arg214fsX12) mutation in exon 5, the expected truncated product of 30 kDa was present [21]. All mutations identified so far in the PQBP1 gene lead to the disturbance or deletion of the C-terminal region in the protein. This domain has been shown to bind to U5-15 kDa [13] a component of
Table 3 Comparison of manifestations in our family and the original family of Renpenning [8].
Mutation Affected males Short stature (<3rd centile) Lean body build Microcephaly (<3rd centile) Upslanting palpebrae Large ears Cupped ears Short philtrum Small mouth Highly arched palate Central balding Small testes <10 ml
Renpenning et al. (1962) [8,15]
This report
c.641insC 20 6/10 3/4 13/14 4/4 1/10 0/5 5/5 0/5 0/5 3/5 4/9
c.631insA 3 3/3 3/3 3/3 3/3 3/3 3/3 0/3 0/3 3/3 1/3 1/3
Slow development/mental retardation Mild (IQ 50e70) 1/14 Severe (IQ <50) 13/14
1/3 3/3
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A recent work of Takahashi et al. [22] proposed that the nematode homologue of PQBP1 is involved in lipid metabolism of intestinal cells. Dysfunction of lipid metabolism might underlie lean body; in fact the majority of patients with PQBP1 mutation presented a slender posture and a lean body habitus. We propose that lean body must be added to the distinguishing features of PQBP1related syndrome especially for adult patients. Our data further confirm that PQBP1 gene should be tested for males showing mental retardation, short stature, lean body and microcephaly. Reported mutations in the PQBP1 involve all domains of the PQBP1 protein, and there is considerable inter- and intrafamilial phenotypic variation. Taking into account all mutations in the PQBP1gene that have been described, five groups of mutations can be classified according to the domain involved (see Table 1): missense mutation involving the WW domain [9], gross deletions involving the PRD domain [16], deletion or duplication of AG nucleotides affecting the DR/ER repeat in the PRD domain [7,10,23], deletion of AG nucleotides affecting the NLS domain [15] and small insertion involving the C-terminal region [15]. In fact Kalscheuer et al. [7] found three different frame shift mutations in the DR/ER repeat in the polar-aminoacid-rich domain (PRD) of the gene PQBP1 in five families including patients with Sutherlan-Haan syndrome [24] Hamel cerebropalatocardiac syndrome [25] and non-syndromic XLMR [26], the same mutations were found by Stevenson et al. as well as Martinez-Garay et al. [23], though reported phenotype was apparently different. However, as MR, microcephaly, short stature and lean habitus seem to be consistent findings among individuals with PQBP1 mutations, patients with these findings should be included in any tested scheme. 5. Conclusions In conclusion, our data further confirm that mentally retarded males with PQBP1 mutations share some common clinical symptoms. The emerging PQBP1-related phenotypes including mild to severe mental retardation, microcephaly, short stature, and lean body build. Therefore, mutation analysis of the PQBP1 gene is warranted for mentally retarded patients with this phenotype especially when family data are compatible with X-linked inheritance. Conflicts of interest The authors declare that they have no conflicts of interests. Acknowledgments We express our gratitude to the family for their active collaboration in the present study. References [1] R. Lehrke, Theory of X-linkage of major intellectual traits, Am. J. Ment. Defic. 76 (1972) 611e619. [2] H.H. Ropers, B.C. Hamel, X-linked mental retardation, Nat. Rev. Genet. 6 (2005) 46e57.
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