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Holoprosencephaly with cerebellar vermis hypoplasia in 13q deletion syndrome: Critical region for cerebellar dysgenesis within 13q32.2q34
Brain & Development 37 (2015) 714–718 www.elsevier.com/locate/braindev
Case Report
Holoprosencephaly with cerebellar vermis hypoplasia in 13q deletion syndrome: Critical region for cerebellar dysgenesis within 13q32.2q34 Masakazu Mimaki a,⇑, Takashi Shiihara b, Mio Watanabe b, Kyoko Hirakata c, Satoru Sakazume d, Akio Ishiguro a, Keiko Shimojima e, Toshiyuki Yamamoto e, Akira Oka a, Masashi Mizuguchi a,f a
Department of Pediatrics, Graduate School of Medicine, The University of Tokyo, Japan b Department of Neurology, Gunma Children’s Medical Center, Japan c Department of Ophthalmology, Gunma Children’s Medical Center, Japan d Clinical Genetics Center, Dokkyo Medical University Koshigaya Hospital, Japan e Tokyo Women’s Medical University Institute for Integrated Medical Sciences, Japan f Developmental Medical Sciences, Graduate School of Medicine, The University of Tokyo, Japan Received 8 July 2014; received in revised form 4 October 2014; accepted 16 October 2014
Abstract We describe two unrelated patients with terminal deletions in the long arm of chromosome 13 showing brain malformation consisting of holoprosencephaly and cerebellar vermis hypoplasia. Array comparative genomic hybridization analysis revealed a pure terminal deletion of 13q31.3q34 in one patient and a mosaic ring chromosome with 13q32.2q34 deletion in the other. Mutations in ZIC2, located within region 13q32, cause holoprosencephaly, whereas the 13q32.2q32.3 region is associated with cerebellar vermis hypoplasia (Dandy–Walker syndrome). The rare concurrence of these major brain malformations in our patients provides further evidence that 13q32.2q32.3 deletion, harboring ZIC2 and ZIC5, leads to cerebellar dysgenesis. Ó 2014 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved.
Keywords: Chromosome 13; Distal 13q deletion; Cerebellar vermis hypoplasia
1. Introduction Variable central nervous system (CNS) anomalies such as holoprosencephaly (HPE), agenesis of the corpus callosum, neural tube defects (NTDs), and Dandy–Walker malformation (DWM) have been reported in the 13q deletion syndrome [1–6]. However,
the concurrent occurrence of HPE and DWM, which is characterized by cerebellar vermis hypoplasia or aplasia, is rare [3]. Here we present the clinical features and molecular cytogenetic characterizations of two patients with 13q deletion including the 13q32.2q34 region. Both patients exhibited multiple anomalies, including HPE and cerebellar vermis hypoplasia.
⇑ Corresponding author at: Department of Pediatrics, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan. Tel.: +81 3 5800 8659; fax: +81 3 3816 4108. E-mail address: [email protected] (M. Mimaki).
http://dx.doi.org/10.1016/j.braindev.2014.10.009 0387-7604/Ó 2014 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved.
M. Mimaki et al. / Brain & Development 37 (2015) 714–718
2. Clinical reports 2.1. Patient 1 Patient 1 was the second child of a 32-year-old mother. His family history was unremarkable. He was born at term (37 weeks) with a normal birth weight (3404 g, +1.0 SD), although he exhibited marked macrocephaly (45-cm head circumference, +8.4 SD). Physical examination showed upslanted palpebral fissures, hypertelorism, low-set malformed ears, a broad prominent nasal bridge, micrognathia, micropenis, hypospadias, bifid scrotum, and a low-level imperforate anus. Ophthalmologic examination revealed chorioretinal coloboma, optic nerve hypoplasia, and narrowing and tortuosity of retinal arterioles. Cardiac ultrasonography
715
revealed a patent foramen ovale and patent ductus arteriosus. Brain magnetic resonance imaging (MRI) on the 18th day and brain computed tomography (CT) on the 27th day after birth revealed alobar HPE with hydrocephalus and marked cerebellar hypoplasia (Fig. 1A–C). Because of an increase in his head circumference, a ventriculoperitoneal shunt was created, and the child was discharged 54 days after birth. Giemsa banding chromosomal analysis of peripheral blood lymphocytes revealed a deletion of the long arm of chromosome 13 (Fig. 2A). Only one signal was detected at the end of the long arm of chromosome 13 by fluorescence in situ hybridization (FISH) using subtelomeric probes, indicating a subtelomeric deletion of 13q (Fig. 2C). Further analysis by array comparative genomic hybridization (aCGH) using the Human
Fig. 1. Radiological brain images of patient 1 (A–C) and patient 2 (D–F) showing brain malformations associated with 13q31.3q34 deletion (patient 1) or 13q32.2q34 deletion (patient 2). (A) Axial T2-weighted magnetic resonance image shows a large dorsal cyst communicating with the prosencephalic common ventricle, and the pancake-like appearance of the remaining cerebral tissue in the anterior portion of the carvarium. These defects are compatible with alobar holoprosencephaly. (B) Sagittal T2-weighted magnetic resonance image shows severe hydrocephalus and cerebellar vermis hypoplasia. (C) Computed axial tomographic image obtained 1 week after ventriculoperitoneal shunting shows severe cerebellar hypoplasia. (D–F) Brain magnetic resonance images of patient 2 at 1 month of age. (D) Axial T1-weighted image. (E) Sagittal T1-weighted image. (F) Coronal T2-weighted image. Hypoplasia of the corpus callosum and absence of the callosal body is shown in (E) (white arrow). Absence of the septum pellucidum and interhemispheric fissure at the parietal region are shown in (F) (black arrow), compatible with syntelencephaly. Cerebellar vermis hypoplasia (white arrowheads) is also demonstrated in (E) and (F).
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M. Mimaki et al. / Brain & Development 37 (2015) 714–718
Genome CGH Microarray 105A chip (Agilent Technologies, Santa Clara, CA, USA), according to methods described elsewhere [7], identified a 21.5-Mb deletion from 13q31.3 to 13qter (93,191,961//114,364,328; NCBI Build 38; Fig. 3A) without additional copy number aberrations in other chromosomal regions [karyotype: 46,XY,del(13)(q31.3q34)]. 2.2. Patient 2 Patient 2 was 1 year and 9 months old at the last follow-up visit. She was the second of two children born to unrelated parents, with an unremarkable family history. Ultrasonography revealed fetal growth retardation and cerebral ventriculomegaly at 28 and 33 weeks of
A
C
gestation, respectively. She was born at 39 weeks of gestation with a low birth weight (1726 g, 3.2 SD) and height (41 cm, 3.5 SD), and her head circumference was 27.8 cm ( 3.6 SD). Physical examination showed anal atresia and dysmorphic features, including upslanted palpebral fissures, hypertelorism, low-set ears, a broad prominent nasal bridge, and micrognathia. Ophthalmologic examination revealed exotropia, persistent pupillary membranes, chorioretinal coloboma, optic nerve hypoplasia, narrowing and tortuosity of retinal arterioles, and mottled fundi. Cardiac ultrasonography revealed a ventricular septal defect and patent ductus arteriosus. Brain MRI at 1 month of age revealed fusion of the middle portion of the cerebral hemispheres (syntelencephaly) (Fig. 1D and F). The cerebellar vermis
B
DB
Fig. 2. Chromosomal karyotyping and FISH analyses of patient 1 (A, C) and patient 2 (B, D). (A) Subtelomeric deletion of chromosome 13q (arrow) is shown in patient 1. (B) Mosaic ring chromosome 13 in patient 2 (right). Partial deletion of 13q (13q32.2q34) is compared with the ideogram of chromosome 13. (C) Only one signal from 13q34 was detected in patient 1. (D) Although the RP11-13I8 probe for 13q14.11 (arrow heads) is visible on both chromosomes, the RP11-1148D4 probe containing ZIC5 and ZIC2 (arrow) is not visible on r(13) in patient 2.
M. Mimaki et al. / Brain & Development 37 (2015) 714–718
A
q31.3
B
3. Discussion
ZIC5 ZIC2
q32.2
q34 -2 -1 0 +1 +2
717
-2 -1 0 +1 +2 (log2)
Fig. 3. Genomic copy number aberrations of both patients demonstrated by CGH Analytics version 3.5 (Agilent) with Chromosome View. (A) Patient 1. (B) Patient 2. The grey boxes indicate aberration regions in both patients. The locations of ZIC2 and ZIC5 are indicated (<).
was hypoplastic (Fig. 1E and F). She showed severe developmental retardation at 1 year and 8 months of age and was unable to control her head or utter meaningful words. Giemsa banding chromosomal analysis of peripheral blood lymphocytes revealed a mosaic ring chromosome 13 (Fig. 2B), and aCGH demonstrated a deletion of approximately 16.4 Mb (98,266,667–114,364,328) (NCBI Build 38) from 13q32.2 to the telomere (Fig. 3B). FISH analysis using five human BAC clone libraries (RP11-13I8 at chr13:41,402,236–41,593,291, RP11-464I2 at chr13:94,492,193–94,674,677, RP111148D4 at chr13:99,320,799–99,476,790, RP11-2L10 at chr13:102,337,773–102,514,754, and RP11-569D9 at chr13:113,930,807–114,103,243 [position referring Build38]) confirmed deletion of 13q32.3, a region containing the genes encoding the developmentally regulated zinc finger transcription factors ZIC2 and ZIC5 (Fig. 2D). The karyotype of this patient was mos 46,XX,r(13)(p13q32.2)del(13)(q32.2q34)[46]/45,XX,-13[4]. ish r(13)(RP11-13I8+,RP11-464I2+,RP11-1148D4 , RP11-2L10 ,RP11-569D9 ).
As demonstrated by aCGH, both our patients harbored a deletion in the long arm of chromosome 13 from 13q32.2 to 13q34. Patient 2 had a mosaic ring chromosome 13, however, considering that cells carrying 13q monosomy cannot survive in the process of development, we speculate that the percentage of these cells was not only low in the peripheral blood lymphocytes but also low in the brain of Patient 2. We thus consider that the ring chromosome with 13q deletion has a pivotal role in the brain malformation of this patient. Heterozygous mutation or deletion of ZIC2, located at 13q32.3, can lead to severe developmental brain anomaly HPE [8]. Marcorelles et al. [9] described 5 second- and third-trimester fetuses with syntelencephaly (or middle hemispheric fusion), the milder HPE variant found in our patient 2, and suggested a causal relationship between syntelencephaly and loss of ZIC2. In the present study, we identified the deletion site associated with HPE as 13q32.2q34, further suggesting an association between ZIC2 haploinsufficiency and HPE. The coexistence of HPE and cerebellar hypoplasia is rare, probably because the master genes that govern morphogenesis differ between the forebrain and hindbrain. Only two such 13q deletion syndrome patients with these concurrent defects have been reported [3], one with del(13)(q21q34) and the other del(13)(q22q33), both exhibiting a combination of HPE and Dandy– Walker malformation (DWM) including cerebellar vermis hypoplasia or aplasia. In the literature, authors speculated that haploinsufficiency of ZIC2 causes HPE, whereas other dosage-sensitive gene(s) in 13q22q33 cause cerebellar hypoplasia [3]. This notion was supported by another report of a del (13)(q14q34) fetus with DWM and agenesis of the cerebellar vermis [4]. Ballarati et al. reported four patients with 13q partial deletions and malformations in the posterior fossa [2]. Using aCGH analysis, they narrowed down the region responsible for DWM to 13q32.2.q33.2, suggesting the involvement of ZIC2 as well as ZIC5, which is also located within this interval. Kirchhoff et al. further refined the DWM-associated region to 13q32.2q33.1 [6] and Mademont-Soler et al. reported a patient with the de novo interstitial deletion del(13)(q32.2q32.3) also presenting with DWM, again consistent with the hypothesis that loss of both ZIC2 and ZIC5 are required for DWM [10]. Although no ZIC5 mutations have yet been described in humans, a mouse study showed that ZIC5 was expressed in the dorsal area of the brain and spinal cord, whereas ZIC5 deficiency in mice resulted in NTD that included the hindbrain [11,12]. Two other members of the ZIC gene family, ZIC1 and ZIC4, map to chromosome 3 in a configuration similar to that of ZIC2 and ZIC5 on chromosome 13. It has been hypothesized that
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heterozygotic loss of both ZIC1 and ZIC4 may cause DWM in patients with 3q deletion [12], and it is thus plausible that the loss of ZIC2 and ZIC5 on chromosome 13 causes malformations of the posterior fossa. Grinberg and Millen [12] suggested that the loss of ZIC2 may lead to HPE, whereas the loss of both ZIC2 and ZIC5 may lead to DWM. Among the patients reported by Ballarati et al. [2] and Kirchhoff et al. [6], all seven patients with cerebellar hypoplasia or DWM had deletions involving the entire 13q32 region, which deletes both ZIC2 and ZIC5, and is within the regions lost in our patients. However, there have been no descriptions of cerebellar hypoplasia in HPE patients carrying mutations in ZIC2 [8,13]. Furthermore, Chabchoub et al. [14] described patients with ZIC2 microdeletions and suggested that mutations and/or deletions of both ZIC5 and ZIC2 are involved in the NTD spectrum, HPE or DWM and ZIC5 could be a modifier gene. Taken together, we speculate that in our patients, the ZIC2 deletion caused HPE and that simultaneous deletion of ZIC2 and ZIC5 caused cerebellar vermis hypoplasia. This is the first report of patients with rare concurrent HPE and cerebellar vermis hypoplasia analyzed by aCGH. Our study provides additional evidence that the deletion of 13q32.3q32.3 causes cerebellar hypoplasia, possibly by haploinsufficiency of ZIC2 and ZIC5.
Acknowledgments We thank Dr. W.B. Dobyns for providing valuable insight on our patient 2. This work is supported by the Program for Promoting the Establishment of Strategic Research Centers, Special Coordination Funds for Promoting Science and Technology, Ministry of Education, Culture, Sports, Science and Technology (Japan). References [1] Brown S, Russo J, Chitayat D, Warburton D. The 13q-syndrome: the molecular definition of a critical deletion region in band 13q32. Am J Hum Genet 1995;57:859–66.
[2] Ballarati L, Rossi E, Bonati MT, Gimelli S, Maraschio P, Finelli P, et al. 13q Deletion and central nervous system anomalies: further insights from karyotype–phenotype analyses of 14 patients. J Med Genet 2007;44:e60. [3] McCormack Jr WM, Shen JJ, Curry SM, Berend SA, Kashork C, Pinar H, et al. Partial deletions of the long arm of chromosome 13 associated with holoprosencephaly and the Dandy–Walker malformation. Am J Med Genet 2002;112:384–9. [4] Alanay Y, Aktas D, Utine E, Talim B, Onderoglu L, Caglar M, et al. Is Dandy–Walker malformation associated with “distal 13q deletion syndrome”? Findings in a fetus supporting previous observations. Am J Med Genet A 2005;136:265–8. [5] Quelin C, Bendavid C, Dubourg C, de la Rochebrochard C, Lucas J, Henry C, et al. Twelve new patients with 13q deletion syndrome: genotype–phenotype analyses in progress. Eur J Med Genet 2009;52:41–6. [6] Kirchhoff M, Bisgaard AM, Stoeva R, Dimitrov B, GillessenKaesbach G, Fryns JP, et al. Phenotype and 244k array-CGH characterization of chromosome 13q deletions: an update of the phenotypic map of 13q21.1-qter. Am J Med Genet A 2009;149A:894–905. [7] Shimojima K, Paez MT, Kurosawa K, Yamamoto T. Proximal interstitial 1p36 deletion syndrome: the most proximal 3.5-Mb microdeletion identified on a dysmorphic and mentally retarded patient with inv(3)(p14.1q26.2). Brain Dev 2009;31:629–33. [8] Brown SA, Warburton D, Brown LY, Yu CY, Roeder ER, Stengel-Rutkowski S, et al. Holoprosencephaly due to mutations in ZIC2, a homologue of Drosophila odd-paired. Nat Genet 1998;20:180–3. [9] Marcorelles P, Loget P, Fallet-Bianco C, Roume J, Encha-Razavi F, Delezoide AL. Unusual variant of holoprosencephaly in monosomy 13q. Pediatr Dev Pathol 2002;5:170–8. [10] Mademont-Soler I, Morales C, Armengol L, Soler A, Sanchez A. Description of the smallest critical region for Dandy–Walker malformation in chromosome 13 in a girl with a cryptic deletion related to t(6;13)(q23;q32). Am J Med Genet A 2010;152A:2308–12. [11] Inoue T, Hatayama M, Tohmonda T, Itohara S, Aruga J, Mikoshiba K. Mouse Zic5 deficiency results in neural tube defects and hypoplasia of cephalic neural crest derivatives. Dev Biol 2004;270:146–62. [12] Grinberg I, Millen KJ. The ZIC gene family in development and disease. Clin Genet 2005;67:290–6. [13] Roessler E, Lacbawan F, Dubourg C, Paulussen A, Herbergs J, Hehr U, et al. The full spectrum of holoprosencephaly-associated mutations within the ZIC2 gene in humans predicts loss-offunction as the predominant disease mechanism. Hum Mutat 2009;30:E541–54. [14] Chabchoub E, Willekens D, Vermeesch JR, Fryns JP. Holoprosencephaly and ZIC2 microdeletions: novel clinical and epidemiological specificities delineated. Clin Genet 2012;81:584–9.
Case Report
Holoprosencephaly with cerebellar vermis hypoplasia in 13q deletion syndrome: Critical region for cerebellar dysgenesis within 13q32.2q34 Masakazu Mimaki a,⇑, Takashi Shiihara b, Mio Watanabe b, Kyoko Hirakata c, Satoru Sakazume d, Akio Ishiguro a, Keiko Shimojima e, Toshiyuki Yamamoto e, Akira Oka a, Masashi Mizuguchi a,f a
Department of Pediatrics, Graduate School of Medicine, The University of Tokyo, Japan b Department of Neurology, Gunma Children’s Medical Center, Japan c Department of Ophthalmology, Gunma Children’s Medical Center, Japan d Clinical Genetics Center, Dokkyo Medical University Koshigaya Hospital, Japan e Tokyo Women’s Medical University Institute for Integrated Medical Sciences, Japan f Developmental Medical Sciences, Graduate School of Medicine, The University of Tokyo, Japan Received 8 July 2014; received in revised form 4 October 2014; accepted 16 October 2014
Abstract We describe two unrelated patients with terminal deletions in the long arm of chromosome 13 showing brain malformation consisting of holoprosencephaly and cerebellar vermis hypoplasia. Array comparative genomic hybridization analysis revealed a pure terminal deletion of 13q31.3q34 in one patient and a mosaic ring chromosome with 13q32.2q34 deletion in the other. Mutations in ZIC2, located within region 13q32, cause holoprosencephaly, whereas the 13q32.2q32.3 region is associated with cerebellar vermis hypoplasia (Dandy–Walker syndrome). The rare concurrence of these major brain malformations in our patients provides further evidence that 13q32.2q32.3 deletion, harboring ZIC2 and ZIC5, leads to cerebellar dysgenesis. Ó 2014 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved.
Keywords: Chromosome 13; Distal 13q deletion; Cerebellar vermis hypoplasia
1. Introduction Variable central nervous system (CNS) anomalies such as holoprosencephaly (HPE), agenesis of the corpus callosum, neural tube defects (NTDs), and Dandy–Walker malformation (DWM) have been reported in the 13q deletion syndrome [1–6]. However,
the concurrent occurrence of HPE and DWM, which is characterized by cerebellar vermis hypoplasia or aplasia, is rare [3]. Here we present the clinical features and molecular cytogenetic characterizations of two patients with 13q deletion including the 13q32.2q34 region. Both patients exhibited multiple anomalies, including HPE and cerebellar vermis hypoplasia.
⇑ Corresponding author at: Department of Pediatrics, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan. Tel.: +81 3 5800 8659; fax: +81 3 3816 4108. E-mail address: [email protected] (M. Mimaki).
http://dx.doi.org/10.1016/j.braindev.2014.10.009 0387-7604/Ó 2014 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved.
M. Mimaki et al. / Brain & Development 37 (2015) 714–718
2. Clinical reports 2.1. Patient 1 Patient 1 was the second child of a 32-year-old mother. His family history was unremarkable. He was born at term (37 weeks) with a normal birth weight (3404 g, +1.0 SD), although he exhibited marked macrocephaly (45-cm head circumference, +8.4 SD). Physical examination showed upslanted palpebral fissures, hypertelorism, low-set malformed ears, a broad prominent nasal bridge, micrognathia, micropenis, hypospadias, bifid scrotum, and a low-level imperforate anus. Ophthalmologic examination revealed chorioretinal coloboma, optic nerve hypoplasia, and narrowing and tortuosity of retinal arterioles. Cardiac ultrasonography
715
revealed a patent foramen ovale and patent ductus arteriosus. Brain magnetic resonance imaging (MRI) on the 18th day and brain computed tomography (CT) on the 27th day after birth revealed alobar HPE with hydrocephalus and marked cerebellar hypoplasia (Fig. 1A–C). Because of an increase in his head circumference, a ventriculoperitoneal shunt was created, and the child was discharged 54 days after birth. Giemsa banding chromosomal analysis of peripheral blood lymphocytes revealed a deletion of the long arm of chromosome 13 (Fig. 2A). Only one signal was detected at the end of the long arm of chromosome 13 by fluorescence in situ hybridization (FISH) using subtelomeric probes, indicating a subtelomeric deletion of 13q (Fig. 2C). Further analysis by array comparative genomic hybridization (aCGH) using the Human
Fig. 1. Radiological brain images of patient 1 (A–C) and patient 2 (D–F) showing brain malformations associated with 13q31.3q34 deletion (patient 1) or 13q32.2q34 deletion (patient 2). (A) Axial T2-weighted magnetic resonance image shows a large dorsal cyst communicating with the prosencephalic common ventricle, and the pancake-like appearance of the remaining cerebral tissue in the anterior portion of the carvarium. These defects are compatible with alobar holoprosencephaly. (B) Sagittal T2-weighted magnetic resonance image shows severe hydrocephalus and cerebellar vermis hypoplasia. (C) Computed axial tomographic image obtained 1 week after ventriculoperitoneal shunting shows severe cerebellar hypoplasia. (D–F) Brain magnetic resonance images of patient 2 at 1 month of age. (D) Axial T1-weighted image. (E) Sagittal T1-weighted image. (F) Coronal T2-weighted image. Hypoplasia of the corpus callosum and absence of the callosal body is shown in (E) (white arrow). Absence of the septum pellucidum and interhemispheric fissure at the parietal region are shown in (F) (black arrow), compatible with syntelencephaly. Cerebellar vermis hypoplasia (white arrowheads) is also demonstrated in (E) and (F).
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M. Mimaki et al. / Brain & Development 37 (2015) 714–718
Genome CGH Microarray 105A chip (Agilent Technologies, Santa Clara, CA, USA), according to methods described elsewhere [7], identified a 21.5-Mb deletion from 13q31.3 to 13qter (93,191,961//114,364,328; NCBI Build 38; Fig. 3A) without additional copy number aberrations in other chromosomal regions [karyotype: 46,XY,del(13)(q31.3q34)]. 2.2. Patient 2 Patient 2 was 1 year and 9 months old at the last follow-up visit. She was the second of two children born to unrelated parents, with an unremarkable family history. Ultrasonography revealed fetal growth retardation and cerebral ventriculomegaly at 28 and 33 weeks of
A
C
gestation, respectively. She was born at 39 weeks of gestation with a low birth weight (1726 g, 3.2 SD) and height (41 cm, 3.5 SD), and her head circumference was 27.8 cm ( 3.6 SD). Physical examination showed anal atresia and dysmorphic features, including upslanted palpebral fissures, hypertelorism, low-set ears, a broad prominent nasal bridge, and micrognathia. Ophthalmologic examination revealed exotropia, persistent pupillary membranes, chorioretinal coloboma, optic nerve hypoplasia, narrowing and tortuosity of retinal arterioles, and mottled fundi. Cardiac ultrasonography revealed a ventricular septal defect and patent ductus arteriosus. Brain MRI at 1 month of age revealed fusion of the middle portion of the cerebral hemispheres (syntelencephaly) (Fig. 1D and F). The cerebellar vermis
B
DB
Fig. 2. Chromosomal karyotyping and FISH analyses of patient 1 (A, C) and patient 2 (B, D). (A) Subtelomeric deletion of chromosome 13q (arrow) is shown in patient 1. (B) Mosaic ring chromosome 13 in patient 2 (right). Partial deletion of 13q (13q32.2q34) is compared with the ideogram of chromosome 13. (C) Only one signal from 13q34 was detected in patient 1. (D) Although the RP11-13I8 probe for 13q14.11 (arrow heads) is visible on both chromosomes, the RP11-1148D4 probe containing ZIC5 and ZIC2 (arrow) is not visible on r(13) in patient 2.
M. Mimaki et al. / Brain & Development 37 (2015) 714–718
A
q31.3
B
3. Discussion
ZIC5 ZIC2
q32.2
q34 -2 -1 0 +1 +2
717
-2 -1 0 +1 +2 (log2)
Fig. 3. Genomic copy number aberrations of both patients demonstrated by CGH Analytics version 3.5 (Agilent) with Chromosome View. (A) Patient 1. (B) Patient 2. The grey boxes indicate aberration regions in both patients. The locations of ZIC2 and ZIC5 are indicated (<).
was hypoplastic (Fig. 1E and F). She showed severe developmental retardation at 1 year and 8 months of age and was unable to control her head or utter meaningful words. Giemsa banding chromosomal analysis of peripheral blood lymphocytes revealed a mosaic ring chromosome 13 (Fig. 2B), and aCGH demonstrated a deletion of approximately 16.4 Mb (98,266,667–114,364,328) (NCBI Build 38) from 13q32.2 to the telomere (Fig. 3B). FISH analysis using five human BAC clone libraries (RP11-13I8 at chr13:41,402,236–41,593,291, RP11-464I2 at chr13:94,492,193–94,674,677, RP111148D4 at chr13:99,320,799–99,476,790, RP11-2L10 at chr13:102,337,773–102,514,754, and RP11-569D9 at chr13:113,930,807–114,103,243 [position referring Build38]) confirmed deletion of 13q32.3, a region containing the genes encoding the developmentally regulated zinc finger transcription factors ZIC2 and ZIC5 (Fig. 2D). The karyotype of this patient was mos 46,XX,r(13)(p13q32.2)del(13)(q32.2q34)[46]/45,XX,-13[4]. ish r(13)(RP11-13I8+,RP11-464I2+,RP11-1148D4 , RP11-2L10 ,RP11-569D9 ).
As demonstrated by aCGH, both our patients harbored a deletion in the long arm of chromosome 13 from 13q32.2 to 13q34. Patient 2 had a mosaic ring chromosome 13, however, considering that cells carrying 13q monosomy cannot survive in the process of development, we speculate that the percentage of these cells was not only low in the peripheral blood lymphocytes but also low in the brain of Patient 2. We thus consider that the ring chromosome with 13q deletion has a pivotal role in the brain malformation of this patient. Heterozygous mutation or deletion of ZIC2, located at 13q32.3, can lead to severe developmental brain anomaly HPE [8]. Marcorelles et al. [9] described 5 second- and third-trimester fetuses with syntelencephaly (or middle hemispheric fusion), the milder HPE variant found in our patient 2, and suggested a causal relationship between syntelencephaly and loss of ZIC2. In the present study, we identified the deletion site associated with HPE as 13q32.2q34, further suggesting an association between ZIC2 haploinsufficiency and HPE. The coexistence of HPE and cerebellar hypoplasia is rare, probably because the master genes that govern morphogenesis differ between the forebrain and hindbrain. Only two such 13q deletion syndrome patients with these concurrent defects have been reported [3], one with del(13)(q21q34) and the other del(13)(q22q33), both exhibiting a combination of HPE and Dandy– Walker malformation (DWM) including cerebellar vermis hypoplasia or aplasia. In the literature, authors speculated that haploinsufficiency of ZIC2 causes HPE, whereas other dosage-sensitive gene(s) in 13q22q33 cause cerebellar hypoplasia [3]. This notion was supported by another report of a del (13)(q14q34) fetus with DWM and agenesis of the cerebellar vermis [4]. Ballarati et al. reported four patients with 13q partial deletions and malformations in the posterior fossa [2]. Using aCGH analysis, they narrowed down the region responsible for DWM to 13q32.2.q33.2, suggesting the involvement of ZIC2 as well as ZIC5, which is also located within this interval. Kirchhoff et al. further refined the DWM-associated region to 13q32.2q33.1 [6] and Mademont-Soler et al. reported a patient with the de novo interstitial deletion del(13)(q32.2q32.3) also presenting with DWM, again consistent with the hypothesis that loss of both ZIC2 and ZIC5 are required for DWM [10]. Although no ZIC5 mutations have yet been described in humans, a mouse study showed that ZIC5 was expressed in the dorsal area of the brain and spinal cord, whereas ZIC5 deficiency in mice resulted in NTD that included the hindbrain [11,12]. Two other members of the ZIC gene family, ZIC1 and ZIC4, map to chromosome 3 in a configuration similar to that of ZIC2 and ZIC5 on chromosome 13. It has been hypothesized that
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heterozygotic loss of both ZIC1 and ZIC4 may cause DWM in patients with 3q deletion [12], and it is thus plausible that the loss of ZIC2 and ZIC5 on chromosome 13 causes malformations of the posterior fossa. Grinberg and Millen [12] suggested that the loss of ZIC2 may lead to HPE, whereas the loss of both ZIC2 and ZIC5 may lead to DWM. Among the patients reported by Ballarati et al. [2] and Kirchhoff et al. [6], all seven patients with cerebellar hypoplasia or DWM had deletions involving the entire 13q32 region, which deletes both ZIC2 and ZIC5, and is within the regions lost in our patients. However, there have been no descriptions of cerebellar hypoplasia in HPE patients carrying mutations in ZIC2 [8,13]. Furthermore, Chabchoub et al. [14] described patients with ZIC2 microdeletions and suggested that mutations and/or deletions of both ZIC5 and ZIC2 are involved in the NTD spectrum, HPE or DWM and ZIC5 could be a modifier gene. Taken together, we speculate that in our patients, the ZIC2 deletion caused HPE and that simultaneous deletion of ZIC2 and ZIC5 caused cerebellar vermis hypoplasia. This is the first report of patients with rare concurrent HPE and cerebellar vermis hypoplasia analyzed by aCGH. Our study provides additional evidence that the deletion of 13q32.3q32.3 causes cerebellar hypoplasia, possibly by haploinsufficiency of ZIC2 and ZIC5.
Acknowledgments We thank Dr. W.B. Dobyns for providing valuable insight on our patient 2. This work is supported by the Program for Promoting the Establishment of Strategic Research Centers, Special Coordination Funds for Promoting Science and Technology, Ministry of Education, Culture, Sports, Science and Technology (Japan). References [1] Brown S, Russo J, Chitayat D, Warburton D. The 13q-syndrome: the molecular definition of a critical deletion region in band 13q32. Am J Hum Genet 1995;57:859–66.
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