- Email: [email protected]
Identification of 46 CAG repeats within PPP2R2B as probably the shortest pathogenic allele for SCA12
Parkinsonism and Related Disorders 21 (2015) 398e401
Contents lists available at ScienceDirect
Parkinsonism and Related Disorders journal homepage: www.elsevier.com/locate/parkreldis
Short communication
Identification of 46 CAG repeats within PPP2R2B as probably the shortest pathogenic allele for SCA12 Yi Dong a, Jian-Jun Wu a, Zhi-Ying Wu a, b, * a b
Department of Neurology and Institute of Neurology, Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, China Department of Neurology and Institute of Neurology, Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 August 2014 Received in revised form 8 January 2015 Accepted 11 January 2015
Background: Spinocerebellar ataxia type 12 (SCA12) is predominantly characterized by action tremor, followed by slowly progressive cerebellar dysfunction. It is a very rare disorder and only identified in certain countries so far. The current appreciation for phenotypic and genotypic features of SCA12 is still limited. Methods: We investigated CAG copies within PPP2R2B in 29 patients with spinocerebellar ataxia who are excluded from the most common SCA subtypes including SCA1, SCA2, SCA3 and SCA6. The medical data of patients carrying abnormal expanded PPP2R2B allele were reviewed and summarized. Results: We found that 3 patients carried 53, 46 and 54 CAG repeats respectively, while the other 26 cases harbored CAG repeats less than 30. The probably shortest pathogenic allele of 46 repeats was detected in one kindred typically experiencing action tremor. Additionally, compared to the prominent cerebellar ataxia, nystagmus and dysphagia seem to be rare in our SCA12 patients. Conclusions: SCA12 might not be as rare in Chinese as previously assumed. The identification of the shortest pathogenic allele helps to define the minimal limit implicated in the disease onset. Moreover, the disease manifestations distinct from other SCA subtypes could help clinicians to provide timely genetic counseling. © 2015 Elsevier Ltd. All rights reserved.
Keywords: SCA12 PPP2R2B Shortest pathogenic allele Chinese
1. Introduction Autosomal dominant cerebellar ataxias (ADCAs), also termed spinocerebellar ataxias (SCAs), are a group of neurodegenerative disorders characterized by pronounced phenotypic and genotypic heterogeneity. To date, 36 subtypes including 27 causative genes for SCAs have been identified [1]. Although the prevalence of each subtype is various depending on the ethnic populations, SCA12 is an uncommon entity throughout the world. It is characterized by action tremor of diverse body parts, accompanying with a wide range of neurologic manifestations, including cerebellar dysfunction, heper-reflexia, parkinsonism manifestation and cognition impairment. SCA12 is caused by a CAG repeat expansion mutation in the 50 -untranslated
region of the gene PPP2R2B, encoding a brain-specific, regulatory subunit of protein phosphatase 2A [2]. However, the functional impact of abnormal PPP2R2B protein on SCA12 onset remains elusive. Since SCA12 is merely depicted in a handful of pedigrees so far, the knowledge on clinical constellation is still evolving. Moreover, the paucity of SCA12 also raises the question about the diagnostic boundary between normal and pathogenic allele. Here we identified 46 CAG repeats within PPP2R2B as probably the shortest pathogenic allele for SCA12 and reported clinical features of 3 Chinese SCA12 families.
2. Materials and methods 2.1. Subjects
* Corresponding author. Department of Neurology and Institute of Neurology, Huashan Hospital, Shanghai Medical College, Fudan University, 12 Wulumuqi Zhong Road, Shanghai 200040, China. Tel./fax: þ86 21 62483421. E-mail address: [email protected] (Z.-Y. Wu). http://dx.doi.org/10.1016/j.parkreldis.2015.01.006 1353-8020/© 2015 Elsevier Ltd. All rights reserved.
Twenty-nine index patients and their family members were enrolled in the Genetic Clinic of Huashan Hospital between January 2008 and March 2013. All patients had an autosomal dominant pattern of inheritance and were diagnosed as SCAs according to the Harding's criteria [3]. Mutation screenings for SCA1, SCA2, SCA3 and SCA6 were negative in all these participants. The study was approved by Ethics Committee of Huashan Hospital and informed consent was obtained from each participant.
Fig. 1. (A) Pedigrees of 3 SCA12 families. Squares indicate males; circles indicate females; filled squares indicate affected males; filled circles indicate affected females; diagonal lines across symbols indicate deceased individuals; arrows indicate the probands. Numbers under the symbols indicate the number of CAG repeats within PPP2R2B. (B) The direct sequencing chromatogram of CAG repeats within PPP2R2B in the proband of Family 2. The arrow indicates the expanded allele of 46 CAG repeats. (C) The clone sequencing chromatogram of abnormal CAG repeats within PPP2R2B in the proband of Family 2. The arrow indicates the expanded allele of 46 CAG repeats.
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Y. Dong et al. / Parkinsonism and Related Disorders 21 (2015) 398e401
Table 1 The clinical characteristics of three SCA12 pedigrees. Affected subject
Family 1
Family 2
Family 3
III2
III4
II1
II3
II5
III2
II1
Age at onset (yr) (CAG) n in PPP2R2B Onset symptom
54 13/51 Gait disability
47 13/53 Gait disability Yes No Normal Normal HypoYes No Noted No Yes Cerebellar and cortical atrophy
52 10/46 Action tremor of head Yes No Normal Normal Normal Yes No No No Yes Not available
46 15/54 Gait disability
Yes No Normal Normal Normal Yes No Noted No Yes Cerebellar atrophy
54 23/46 Action tremor of hands Yes No Normal Normal HyperYes or No No Noted No Yes Not available
e 10/46 e
Dysarthria Dysphagia Muscle force Muscular tension Reflex Babinski sign Nystagmus Cerebellar ataxia Cognitive decline Action tremor MRI
54 10/46 Action tremor of hands Yes No Normal Normal Normal No No Noted Yes Yes Not available
e e e e e e e e e e Not available
Yes No Normal Normal HyperYes No Noted Yes No Cerebellar and cortical atrophy
2.2. Molecular analyses of PPP2R2B Genomic DNA was extracted from peripheral blood using a QIAamp DNA Blood Minikit (QIAGEN, Hilden, Germany). The fragment of the PPP2R2B gene containing the CAG triplets was amplified according to the previous design [2]. Amplified products were purified with shrimp alkaline phosphatase and exonuclease, then directly sequenced via an ABI 3730 Automated DNA Sequencer (Applied Biosystems). In addition, the pathologic fragment was re-sequenced using plasmid cloning sequencing method in order to improve the quality of chromatogram. The resulting sequences were aligned to the NCBI human reference DNA sequence of PPP2R2B (Ensembl gene ID ENSG00000156475), and the specific size of CAG repeats was determined.
3. Results 3.1. Mutation analysis of PPP2R2B in 29 index patients After genetic investigation of PPP2R2B, we found 3 probands carrying 53, 46, and 54 CAG repeats respectively (Fig. 1A, Family 1e3), while the other 26 cases harbored CAG repeats expansion less than 30. We further investigated CAG repeats of PPP2R2B in the affected family members. In Family 1, the proband's brother (III2) was identified to carry 51 CAG repeats, indicating that the length of CAG triple was unstable in this pedigree. In Family 2, the proband's affected brothers (II3, II5) were detected to harbor the same CAG repeats as well as his asymptomatic son (III2). However, the proband's affected mother was deceased before the recruitment and other members declined genetic investigations in Family 3. The 46 CAG repeats (Fig. 1B, C) detected in Family 2 are identified as probably the shortest pathogenic allele for SCA12. 3.2. Clinical features of SCA12 pedigrees The medical data of SCA12 cases were reviewed and summarized in Table 1. The proband (III4) of Family 1 displayed gait disability and fell to the ground sometimes when he was 47. Two years later, he developed action tremor of his arms. Neurological examinations revealed the absence of deep tendon reflexes. Babinski sign was positive bilaterally. A brain MRI performed at his 51 years displayed cerebellar and cortical atrophy. His father, his paternal aunt and uncle had similar signs of cerebellar dysfunction and passed away approximately 10 years after the onset. His brother (III2) developed gait ataxia at aged 54, but his symptoms progressed slowly in the past 5 years. In Family 2, the 60-year-old proband (II1) experienced action tremor of left arm at 54 years old. One year later, his right arm
became tremulous. He sought medical help in the local hospital and was firstly diagnosed as essential tremor. In the following 2 years, he gradually presented with head tremor. Three and half years later, he developed gait disability and dysarthria. Six months ago, he exhibited mild cognition impairment. His father suffered action tremor of arms and head aged 50 and was deceased 21 years after the onset. His brother (II3) underwent the similar symptoms at aged 54. The deep tendon reflexes were diffusely brisk. Additionally, II5 also presented with action tremor of head aged 52. The brain MRI of this pedigree was not available owing to claustrophobia. In Family 3, the proband (II1) experienced gait ataxia when he was 46 years old. Subsequently, he developed dysarthria and diplopia. His swallow function was intact thus far. Cognition decline appeared at 51 years old and aggravated progressively. Neurological examinations revealed severely ataxic gait. Hoffman's sign in left side was positive. His mother developed similar symptoms, and passed away at 64 years old.
4. Discussion In the current study, we screened CAG repeats within PPP2R2B in 29 SCA index patients who had been excluded for SCA1, SCA2, SCA3 and SCA6. We identified 3 probands harboring 53, 46, 54 CAG repeats respectively. The clinical manifestations of probands and related family members are compatible with those previous reports of SCA12, confirming SCA12 diagnosis. The prevalence of SCA12 is quite low worldwide. Only a few SCA12 pedigrees were explicitly documented in the literature. In addition to several Indian cases due to founder effect [4e6], SCA12 cases were only detected in an American pedigree of German origin [2], one Singaporean pedigree [7], two Italian pedigrees [8], two Chinese Han pedigrees [9,10], and one Chinese pedigree of Uygur descent [11]. Combined with our three families, the incidence of SCA12 in Chinese population seems to be higher than previously conceived. Given the rarity of SCA12, the screening for CAG repeats within PPP2R2B was only performed in a handful of cases. The low threshold of CAG repeats for SCA12 remains to be determined. It is generally suggested that pathological mutation for SCA12 is 51 or more CAG repeats within PPP2R2B [2,4,5]. However, several recent reports threw some doubt on the low threshold. A patient with CreutzfeldJacob disease was reported to carry 49 CAG repeats within PPP2R2B [12]. That case presented with action tremor as the initial
Y. Dong et al. / Parkinsonism and Related Disorders 21 (2015) 398e401
symptom, and developed cerebellar signs that preceded cognitive impairment. Recently, the shortest pathogenic-expanded allele of PPP2R2B was reported to be 47 triplets for SCA12 [11]. In the present study, we reported a family (Family 2) who exhibited typical symptoms of SCA12 and carried 46 CAG repeats within PPP2R2B. The allele of 46 CAG repeats is tightly associated with phenotypes of patients, indicating the pathological mutation is responsible for disease onset in this pedigree. Therefore, the 46 CAG repeats of PPP2R2B is probably the shortest pathogenic allele for SCA12. Typically, the initial symptom of SCA12 is action tremor of arms or head. In our study, only Family 2 initially presented with typical symptoms of action tremor, while Family 1 and Family 3 initially exhibited gait ataxia. Compared to the later development of action tremor in Family 1, Family 3 did not display the core symptom during the disease course so far. The harbinger is not universal among all SCA12 patients. This also implies that the SCA12 phenotype could be heterogeneous, and inter-familial diversity should be considered. This variation further suggests that loss of tremor is scanty to rule out the diagnosis of SCA12. In addition, all the cases in this study suffered from dysarthria in the disease course, but none of them experienced dysphagia. This suggests dysphagia could be rare sign of SCA12. Alternatively, these affected patients could develop dysphagia in the late disease course. However, nystagmus was absent in all our patients, which is consistent with the previous reports of Italian and American SCA12 patients [2,8]. In summary, we presented 3 Chinese SCA12 pedigrees and identified 46 CAG repeats within PPP2R2B as probably the shortest pathogenic allele for SCA12. In addition, our results indicated that SCA12 might not be rare in the Chinese population. Mutation of PPP2R2B is worthy of investigation in those SCAs patients who are negative for SCA1, 2, 3 and 6. Conflicts of interest/financial disclosures The authors declare no conflicts of interest. Acknowledgments This work was supported by the grant from the National Natural Science Foundation to Zhi-Ying Wu (81125009, Beijing). The
401
authors sincerely appreciated the patients for their willingness to participate in the current study. We also thank the anonymous reviewers for their helpful comments. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.parkreldis.2015.01.006. References [1] Musova Z, Sedlacek Z, Mazanec R, Klempir J, Roth J, Plevova P, et al. Spinocerebellar ataxias type 8, 12, and 17 and dentatorubro-pallidoluysian atrophy in Czech ataxic patients. Cerebellum 2013;12:155e61. [2] Holmes SE, O'Hearn EE, McInnis MG, Gorelick-Feldman DA, Kleiderlein JJ, Callahan C, et al. Expansion of a novel CAG trinucleotide repeat in the 50 region of PPP2R2B is associated with SCA12. Nat Genet 1999;23:391e2. [3] Harding AE. Clinical features and classification of inherited ataxias. Adv Neurol 1993;61:1e14. [4] Fujigasaki H, Verma IC, Camuzat A, Margolis RL, Zander C, Lebre AS, et al. SCA12 is a rare locus for autosomal dominant cerebellar ataxia: a study of an Indian family. Ann Neurol 2001;49:117e21. [5] Srivastava AK, Choudhry S, Gopinath MS, Roy S, Tripathi M, Brahmachari SK, et al. Molecular and clinical correlation in five Indian families with spinocerebellar ataxia 12. Ann Neurol 2001;50:796e800. [6] Bahl S, Virdi K, Mittal U, Sachdeva MP, Kalla AK, Holmes SE, et al. Evidence of a common founder for SCA12 in the Indian population. Ann Hum Genet 2005;69:528e34. [7] Zhao Y, Tan EK, Law HY, Yoon CS, Wong MC, Ng I. Prevalence and ethnic differences of autosomal-dominant cerebellar ataxia in Singapore. Clin Genet 2002;62:478e81. [8] Brusco A, Cagnoli C, Franco A, Dragone E, Nardacchione A, Grosso E, et al. Analysis of SCA8 and SCA12 loci in 134 Italian ataxic patients negative for SCA1-3, 6 and 7 CAG expansions. J Neurol 2002;249:923e9. [9] Xie QY, Liang XL, Li XH. Molecular genetics and its clinical application in the diagnosis of spinocerebellar ataxias. Zhonghua Yi Xue Yi Chuan Xue Za Zhi 2005;22:71e3. [10] Wang J, Shen L, Lei L, Xu Q, Zhou J, Liu Y, et al. Spinocerebellar ataxias in mainland China: an updated genetic analysis among a large cohort of familial and sporadic cases. Zhong Nan Da Xue Xue Bao Yi Xue Ban 2011;36: 482e9. [11] Li HT, Lei J, Ma JH, Yu J, Zhang XN. Gene mutation and clinical characteristics of a Chinese Uygur family with spinocerebellar ataxia type 12. Zhonghua Yi Xue Yi Chuan Xue Za Zhi 2011;28:137e41. [12] Hellenbroich Y, Schulz-Schaeffer W, Nitschke MF, Kohnke J, Handler G, Burk K, et al. Coincidence of a large SCA12 repeat allele with a case of Creutzfeld-Jacob disease. J Neurol Neurosurg Psychiatry 2004;75:937e8.
Contents lists available at ScienceDirect
Parkinsonism and Related Disorders journal homepage: www.elsevier.com/locate/parkreldis
Short communication
Identification of 46 CAG repeats within PPP2R2B as probably the shortest pathogenic allele for SCA12 Yi Dong a, Jian-Jun Wu a, Zhi-Ying Wu a, b, * a b
Department of Neurology and Institute of Neurology, Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, China Department of Neurology and Institute of Neurology, Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 August 2014 Received in revised form 8 January 2015 Accepted 11 January 2015
Background: Spinocerebellar ataxia type 12 (SCA12) is predominantly characterized by action tremor, followed by slowly progressive cerebellar dysfunction. It is a very rare disorder and only identified in certain countries so far. The current appreciation for phenotypic and genotypic features of SCA12 is still limited. Methods: We investigated CAG copies within PPP2R2B in 29 patients with spinocerebellar ataxia who are excluded from the most common SCA subtypes including SCA1, SCA2, SCA3 and SCA6. The medical data of patients carrying abnormal expanded PPP2R2B allele were reviewed and summarized. Results: We found that 3 patients carried 53, 46 and 54 CAG repeats respectively, while the other 26 cases harbored CAG repeats less than 30. The probably shortest pathogenic allele of 46 repeats was detected in one kindred typically experiencing action tremor. Additionally, compared to the prominent cerebellar ataxia, nystagmus and dysphagia seem to be rare in our SCA12 patients. Conclusions: SCA12 might not be as rare in Chinese as previously assumed. The identification of the shortest pathogenic allele helps to define the minimal limit implicated in the disease onset. Moreover, the disease manifestations distinct from other SCA subtypes could help clinicians to provide timely genetic counseling. © 2015 Elsevier Ltd. All rights reserved.
Keywords: SCA12 PPP2R2B Shortest pathogenic allele Chinese
1. Introduction Autosomal dominant cerebellar ataxias (ADCAs), also termed spinocerebellar ataxias (SCAs), are a group of neurodegenerative disorders characterized by pronounced phenotypic and genotypic heterogeneity. To date, 36 subtypes including 27 causative genes for SCAs have been identified [1]. Although the prevalence of each subtype is various depending on the ethnic populations, SCA12 is an uncommon entity throughout the world. It is characterized by action tremor of diverse body parts, accompanying with a wide range of neurologic manifestations, including cerebellar dysfunction, heper-reflexia, parkinsonism manifestation and cognition impairment. SCA12 is caused by a CAG repeat expansion mutation in the 50 -untranslated
region of the gene PPP2R2B, encoding a brain-specific, regulatory subunit of protein phosphatase 2A [2]. However, the functional impact of abnormal PPP2R2B protein on SCA12 onset remains elusive. Since SCA12 is merely depicted in a handful of pedigrees so far, the knowledge on clinical constellation is still evolving. Moreover, the paucity of SCA12 also raises the question about the diagnostic boundary between normal and pathogenic allele. Here we identified 46 CAG repeats within PPP2R2B as probably the shortest pathogenic allele for SCA12 and reported clinical features of 3 Chinese SCA12 families.
2. Materials and methods 2.1. Subjects
* Corresponding author. Department of Neurology and Institute of Neurology, Huashan Hospital, Shanghai Medical College, Fudan University, 12 Wulumuqi Zhong Road, Shanghai 200040, China. Tel./fax: þ86 21 62483421. E-mail address: [email protected] (Z.-Y. Wu). http://dx.doi.org/10.1016/j.parkreldis.2015.01.006 1353-8020/© 2015 Elsevier Ltd. All rights reserved.
Twenty-nine index patients and their family members were enrolled in the Genetic Clinic of Huashan Hospital between January 2008 and March 2013. All patients had an autosomal dominant pattern of inheritance and were diagnosed as SCAs according to the Harding's criteria [3]. Mutation screenings for SCA1, SCA2, SCA3 and SCA6 were negative in all these participants. The study was approved by Ethics Committee of Huashan Hospital and informed consent was obtained from each participant.
Fig. 1. (A) Pedigrees of 3 SCA12 families. Squares indicate males; circles indicate females; filled squares indicate affected males; filled circles indicate affected females; diagonal lines across symbols indicate deceased individuals; arrows indicate the probands. Numbers under the symbols indicate the number of CAG repeats within PPP2R2B. (B) The direct sequencing chromatogram of CAG repeats within PPP2R2B in the proband of Family 2. The arrow indicates the expanded allele of 46 CAG repeats. (C) The clone sequencing chromatogram of abnormal CAG repeats within PPP2R2B in the proband of Family 2. The arrow indicates the expanded allele of 46 CAG repeats.
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Y. Dong et al. / Parkinsonism and Related Disorders 21 (2015) 398e401
Table 1 The clinical characteristics of three SCA12 pedigrees. Affected subject
Family 1
Family 2
Family 3
III2
III4
II1
II3
II5
III2
II1
Age at onset (yr) (CAG) n in PPP2R2B Onset symptom
54 13/51 Gait disability
47 13/53 Gait disability Yes No Normal Normal HypoYes No Noted No Yes Cerebellar and cortical atrophy
52 10/46 Action tremor of head Yes No Normal Normal Normal Yes No No No Yes Not available
46 15/54 Gait disability
Yes No Normal Normal Normal Yes No Noted No Yes Cerebellar atrophy
54 23/46 Action tremor of hands Yes No Normal Normal HyperYes or No No Noted No Yes Not available
e 10/46 e
Dysarthria Dysphagia Muscle force Muscular tension Reflex Babinski sign Nystagmus Cerebellar ataxia Cognitive decline Action tremor MRI
54 10/46 Action tremor of hands Yes No Normal Normal Normal No No Noted Yes Yes Not available
e e e e e e e e e e Not available
Yes No Normal Normal HyperYes No Noted Yes No Cerebellar and cortical atrophy
2.2. Molecular analyses of PPP2R2B Genomic DNA was extracted from peripheral blood using a QIAamp DNA Blood Minikit (QIAGEN, Hilden, Germany). The fragment of the PPP2R2B gene containing the CAG triplets was amplified according to the previous design [2]. Amplified products were purified with shrimp alkaline phosphatase and exonuclease, then directly sequenced via an ABI 3730 Automated DNA Sequencer (Applied Biosystems). In addition, the pathologic fragment was re-sequenced using plasmid cloning sequencing method in order to improve the quality of chromatogram. The resulting sequences were aligned to the NCBI human reference DNA sequence of PPP2R2B (Ensembl gene ID ENSG00000156475), and the specific size of CAG repeats was determined.
3. Results 3.1. Mutation analysis of PPP2R2B in 29 index patients After genetic investigation of PPP2R2B, we found 3 probands carrying 53, 46, and 54 CAG repeats respectively (Fig. 1A, Family 1e3), while the other 26 cases harbored CAG repeats expansion less than 30. We further investigated CAG repeats of PPP2R2B in the affected family members. In Family 1, the proband's brother (III2) was identified to carry 51 CAG repeats, indicating that the length of CAG triple was unstable in this pedigree. In Family 2, the proband's affected brothers (II3, II5) were detected to harbor the same CAG repeats as well as his asymptomatic son (III2). However, the proband's affected mother was deceased before the recruitment and other members declined genetic investigations in Family 3. The 46 CAG repeats (Fig. 1B, C) detected in Family 2 are identified as probably the shortest pathogenic allele for SCA12. 3.2. Clinical features of SCA12 pedigrees The medical data of SCA12 cases were reviewed and summarized in Table 1. The proband (III4) of Family 1 displayed gait disability and fell to the ground sometimes when he was 47. Two years later, he developed action tremor of his arms. Neurological examinations revealed the absence of deep tendon reflexes. Babinski sign was positive bilaterally. A brain MRI performed at his 51 years displayed cerebellar and cortical atrophy. His father, his paternal aunt and uncle had similar signs of cerebellar dysfunction and passed away approximately 10 years after the onset. His brother (III2) developed gait ataxia at aged 54, but his symptoms progressed slowly in the past 5 years. In Family 2, the 60-year-old proband (II1) experienced action tremor of left arm at 54 years old. One year later, his right arm
became tremulous. He sought medical help in the local hospital and was firstly diagnosed as essential tremor. In the following 2 years, he gradually presented with head tremor. Three and half years later, he developed gait disability and dysarthria. Six months ago, he exhibited mild cognition impairment. His father suffered action tremor of arms and head aged 50 and was deceased 21 years after the onset. His brother (II3) underwent the similar symptoms at aged 54. The deep tendon reflexes were diffusely brisk. Additionally, II5 also presented with action tremor of head aged 52. The brain MRI of this pedigree was not available owing to claustrophobia. In Family 3, the proband (II1) experienced gait ataxia when he was 46 years old. Subsequently, he developed dysarthria and diplopia. His swallow function was intact thus far. Cognition decline appeared at 51 years old and aggravated progressively. Neurological examinations revealed severely ataxic gait. Hoffman's sign in left side was positive. His mother developed similar symptoms, and passed away at 64 years old.
4. Discussion In the current study, we screened CAG repeats within PPP2R2B in 29 SCA index patients who had been excluded for SCA1, SCA2, SCA3 and SCA6. We identified 3 probands harboring 53, 46, 54 CAG repeats respectively. The clinical manifestations of probands and related family members are compatible with those previous reports of SCA12, confirming SCA12 diagnosis. The prevalence of SCA12 is quite low worldwide. Only a few SCA12 pedigrees were explicitly documented in the literature. In addition to several Indian cases due to founder effect [4e6], SCA12 cases were only detected in an American pedigree of German origin [2], one Singaporean pedigree [7], two Italian pedigrees [8], two Chinese Han pedigrees [9,10], and one Chinese pedigree of Uygur descent [11]. Combined with our three families, the incidence of SCA12 in Chinese population seems to be higher than previously conceived. Given the rarity of SCA12, the screening for CAG repeats within PPP2R2B was only performed in a handful of cases. The low threshold of CAG repeats for SCA12 remains to be determined. It is generally suggested that pathological mutation for SCA12 is 51 or more CAG repeats within PPP2R2B [2,4,5]. However, several recent reports threw some doubt on the low threshold. A patient with CreutzfeldJacob disease was reported to carry 49 CAG repeats within PPP2R2B [12]. That case presented with action tremor as the initial
Y. Dong et al. / Parkinsonism and Related Disorders 21 (2015) 398e401
symptom, and developed cerebellar signs that preceded cognitive impairment. Recently, the shortest pathogenic-expanded allele of PPP2R2B was reported to be 47 triplets for SCA12 [11]. In the present study, we reported a family (Family 2) who exhibited typical symptoms of SCA12 and carried 46 CAG repeats within PPP2R2B. The allele of 46 CAG repeats is tightly associated with phenotypes of patients, indicating the pathological mutation is responsible for disease onset in this pedigree. Therefore, the 46 CAG repeats of PPP2R2B is probably the shortest pathogenic allele for SCA12. Typically, the initial symptom of SCA12 is action tremor of arms or head. In our study, only Family 2 initially presented with typical symptoms of action tremor, while Family 1 and Family 3 initially exhibited gait ataxia. Compared to the later development of action tremor in Family 1, Family 3 did not display the core symptom during the disease course so far. The harbinger is not universal among all SCA12 patients. This also implies that the SCA12 phenotype could be heterogeneous, and inter-familial diversity should be considered. This variation further suggests that loss of tremor is scanty to rule out the diagnosis of SCA12. In addition, all the cases in this study suffered from dysarthria in the disease course, but none of them experienced dysphagia. This suggests dysphagia could be rare sign of SCA12. Alternatively, these affected patients could develop dysphagia in the late disease course. However, nystagmus was absent in all our patients, which is consistent with the previous reports of Italian and American SCA12 patients [2,8]. In summary, we presented 3 Chinese SCA12 pedigrees and identified 46 CAG repeats within PPP2R2B as probably the shortest pathogenic allele for SCA12. In addition, our results indicated that SCA12 might not be rare in the Chinese population. Mutation of PPP2R2B is worthy of investigation in those SCAs patients who are negative for SCA1, 2, 3 and 6. Conflicts of interest/financial disclosures The authors declare no conflicts of interest. Acknowledgments This work was supported by the grant from the National Natural Science Foundation to Zhi-Ying Wu (81125009, Beijing). The
401
authors sincerely appreciated the patients for their willingness to participate in the current study. We also thank the anonymous reviewers for their helpful comments. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.parkreldis.2015.01.006. References [1] Musova Z, Sedlacek Z, Mazanec R, Klempir J, Roth J, Plevova P, et al. Spinocerebellar ataxias type 8, 12, and 17 and dentatorubro-pallidoluysian atrophy in Czech ataxic patients. Cerebellum 2013;12:155e61. [2] Holmes SE, O'Hearn EE, McInnis MG, Gorelick-Feldman DA, Kleiderlein JJ, Callahan C, et al. Expansion of a novel CAG trinucleotide repeat in the 50 region of PPP2R2B is associated with SCA12. Nat Genet 1999;23:391e2. [3] Harding AE. Clinical features and classification of inherited ataxias. Adv Neurol 1993;61:1e14. [4] Fujigasaki H, Verma IC, Camuzat A, Margolis RL, Zander C, Lebre AS, et al. SCA12 is a rare locus for autosomal dominant cerebellar ataxia: a study of an Indian family. Ann Neurol 2001;49:117e21. [5] Srivastava AK, Choudhry S, Gopinath MS, Roy S, Tripathi M, Brahmachari SK, et al. Molecular and clinical correlation in five Indian families with spinocerebellar ataxia 12. Ann Neurol 2001;50:796e800. [6] Bahl S, Virdi K, Mittal U, Sachdeva MP, Kalla AK, Holmes SE, et al. Evidence of a common founder for SCA12 in the Indian population. Ann Hum Genet 2005;69:528e34. [7] Zhao Y, Tan EK, Law HY, Yoon CS, Wong MC, Ng I. Prevalence and ethnic differences of autosomal-dominant cerebellar ataxia in Singapore. Clin Genet 2002;62:478e81. [8] Brusco A, Cagnoli C, Franco A, Dragone E, Nardacchione A, Grosso E, et al. Analysis of SCA8 and SCA12 loci in 134 Italian ataxic patients negative for SCA1-3, 6 and 7 CAG expansions. J Neurol 2002;249:923e9. [9] Xie QY, Liang XL, Li XH. Molecular genetics and its clinical application in the diagnosis of spinocerebellar ataxias. Zhonghua Yi Xue Yi Chuan Xue Za Zhi 2005;22:71e3. [10] Wang J, Shen L, Lei L, Xu Q, Zhou J, Liu Y, et al. Spinocerebellar ataxias in mainland China: an updated genetic analysis among a large cohort of familial and sporadic cases. Zhong Nan Da Xue Xue Bao Yi Xue Ban 2011;36: 482e9. [11] Li HT, Lei J, Ma JH, Yu J, Zhang XN. Gene mutation and clinical characteristics of a Chinese Uygur family with spinocerebellar ataxia type 12. Zhonghua Yi Xue Yi Chuan Xue Za Zhi 2011;28:137e41. [12] Hellenbroich Y, Schulz-Schaeffer W, Nitschke MF, Kohnke J, Handler G, Burk K, et al. Coincidence of a large SCA12 repeat allele with a case of Creutzfeld-Jacob disease. J Neurol Neurosurg Psychiatry 2004;75:937e8.