Brief Report

 

 

 

 

 

A Large Family with Spinocerebellar Ataxia Type 6 in Iran:

A Clinical and Genetic Study

 

Haruo Shimazaki MD PhD* , Reza Vazifehmand MSc**, Mohhamad-Hassan Heidari PhD**, Hamid-Reza Khorram-Khorshid MD PhD***, Sassan Saber MD**, Shamsodin Hejazi MD,

Fatemeh Aghakhani-Moghadam BSc***, Yi Ouyang MD PhD*, Junko Honda PhD*,

Imaharu Nakano MD PhD*, Yoshihisa Takiyama MD PhD*

 

 

Authors’ affiliations: *Division of Neurology, Department of Internal Medicine, Jichi Medical University, Tochigi, Japan, **Department of Anatomical Sciences, School of Medicine, Shaheed Beheshti University of Medical Sciences, ***Genetic Research Center, The Social Welfare and Rehabilitation Sciences University, Tehran, †Department of Neurologic Sciences, Qom University of Medical Sciences, Qom, Iran, ‡These authors equally contributed to this work.

•Corresponding author and reprints: Yoshihisa Takiyama MD PhD, Department of Neurology, Jichi Medical University, Tochigi 329-0498, Japan.

Tel: +81-285-58-73-52, Fax: +81-285-44-51-18,

E-mail: ytakiya@jichi.ac.jp

Accepted for publication: 23 April 2008

 


The authors describe a large Iranian family with autosomal dominant cerebellar ataxia, which included 14 patients in four generations. We examined seven patients who had expanded CAG repeats in the CACNA1A gene with repeat instability (24 and 25 repeats). Although all patients showed cerebellar ataxia, each patient exhibited peripheral neuropathy or spasticity indicating intrafamilial phenotypic variability.

 

 Archives of Iranian Medicine, Volume 11, Number 4, 2008: 459 – 462.

 

Keywords:  CAG repeats  · Iran · peripheral neuropathy · SCA6 · spasticity


 

 
Introduction

 

S

pinocerebellar ataxia type 6 (SCA6) is an autosomal dominant neurodegenerative disorder characterized by late-onset and slowly progressive pure cerebellar ataxia. Patients with SCA6, however, less frequently manifest non-cerebellar symptoms including peripheral neuropathy and pyramidal signs.1, 2 SCA6 is caused by a CAG repeat expansion in the CACNA1A gene that encodes the α1A voltage-dependent calcium channel subunit.3 To date, SCA6 has been reported from North,4 and South America,5 Europe,1 South Africa,6 Australia,7 and East Asia.8 – 10 We report here a large Iranian family with SCA6 with probable   intergenerational    instability   of   CAG repeats in the CACNA1A gene and intrafamilial phenotypic variability.

 

Materials and Methods

 

The family tree was consistent with autosomal dominant transmission (Figure 1). Four patients with ataxia (II-2, III-7, III-9, and III-21) were thoroughly examined in this family. Information on deceased family members was obtained from senior members of the family. Brain Magnetic Resonance Imaging (MRI) was performed in four patients (II-2, III-7, III-9, and III-21), and a nerve conduction study was performed in one patient (II-2). 

Blood samples were obtained with informed consent from nine members, including seven patients (II-2, II-4, II-8, III-7, III-9, III-13, and III-21). DNA was extracted from peripheral blood leukocytes. Polymerase chain reaction (PCR) was performed to amplify the fragment of the CACNA1A gene containing the CAG repeat with a primer set (S-5-F1 and R1) as described previously.9 The PCR-produced fragment was electrophoresed in a capillary on an automated ABI PRISM 310 genetic analyzer (Applied Biosystems, USA). Analysis was performed by use of GenScan analysis software version 3.1.2 (Applied Biosystems). The CAG repeat sizes were determined by using size markers derived from plasmid DNAs containing 17 and 21 CAG repeats, and a GenScan-500 TAMRA.

This study was approved by the Medical Ethical Committee of Jichi Medical University.

 

 

Figure 1.  Family tree of the Iranian family with SCA6. The numbers below the symbols for the individuals are the CAG repeat numbers in the CACNA1A gene. The gender is unspecified for the fourth generation members, denoted by diamonds to maintain anonymity.

 

Results

 

This large Iranian family included 14 patients with ataxia in four generations. We examined a 43-year-old man (III-9), a 53-year-old man (III-21), a 75-year-old woman (II-2), and a 45-year-old woman (III-7) in this family. The clinical findings in the four patients are summarized in Table 1.  Other three patients (II-4, II-8, and III-13) were described as ataxic cases in the previous medical records. Cerebellar ataxia was found in all four patients. Patient II-2 showed hyporeflexia and decreased vibratory sensation without diabetes mellitus and vitamin B12 deficiency. A peripheral nerve conduction study of this patient disclosed mild reduction of motor nerve conduction velocities in the lower extremities and severe decrease of sensory nerve action potentials with moderately reduced conduction  velocities, indicating peripheral neuropathy (data not shown). Patients III-21 and III-7 exhibited hyperreflexia with Babinski signs. Furthermore, the latter patient showed spasticity of the lower extremities. Brain MRI of all four patients revealed marked cerebellar atrophy without brainstem involvement (data not shown).

 

Table 1.  Clinical features of the patients in the Iranian SCA6 family.

Generation code number

III-9

II-2

III-21

III-7

Age (years)            

44

76

54

46

Sex                         

Male

Female

Male

Female

Age at onset (years)               

36

35

40

33

Age at examination (years)     

43

75

53

45

Cerebellar

 

 

 

 

Ataxic gait          

+

+

+

+

Limb ataxia

+

+

+

+

Truncal ataxia     

+

+

+

+

Vertigo

+

+

+

+

Gaze nystagmus

+

+

+

+

Dysarthria

+

+

+

+

Peripheral

 

 

 

 

Depressed DTRs

-

+

-

-

Disturbance of pinprick

and touch sensation

-

-

-

-

Decreased vibration sense

-

+

-

-

Pyramidal

 

 

 

 

Spasticity

-

-

-

+

Brisk DTRs

-

-

+

+

Babinski sign

-

-

+

+

Extrapyramidal

 

 

 

 

Rigidity

-

-

-

-

Tremor               

-

-

-

-

External ophthalmoplegia

 

 

 

 

Upward gaze paresis

-

-

-

-

Horizontal gaze paresis

-

-

-

-

Slow eye movement               

-

-

-

-

Dementia

-

-

-

-

DTRs: deep tendon reflexes.

 

 

 

 

 

 

The CAG repeat numbers in the family members were as follows: patients II-2, II-8, III-7, and III-9 had 13/24 repeats, whereas II-4 had 13/25 repeats. Patients III-13 and III-21 had 11/24 repeats. Family members without ataxia (III-4 and III-5) had 11/13 repeats (Figure 1).

 

Discussion
 

SCA6 usually includes pure cerebellar ataxia including unsteadiness of gait, horizontal and vertical gaze nystagmus, and dysarthria.9 In the present family, however, it is noteworthy that each patient exhibited peripheral neuropathy or spasticity in addition to cerebellar ataxia.

Peripheral neuropathy in patients with SCA6 has been reported in a few papers so far.1,2 Regarding Japanese patients with SCA6, 15.2% of 140 patients showed hyporeflexia.2 Nerve conduction studies showed normal findings even in patients with hyporeflexia.2 In contrast, nerve conduction studies disclosed mild sensorimotor peripheral neuropathy with axonal and demyelinating elements in six of ten German patients with SCA6.1 Thus, peripheral neuropathy appears to be more frequent in German patients than in Japanese ones.

Meanwhile, pyramidal signs including hyperreflexia, spasticity, and Babinski sign have been documented in 6%, 3.8%, and 1.4% of patients with SCA6, respectively.2 In the present family, two of the four patients showed hyperreflexia and Babinski sign, and one patient showed spasticity in addition to hyperreflexia and Babinski sign.

Schöls et al. described that peripheral neuropathy and spasticity were uncorrelated with CAG repeat length, and that spasticity and neuropathy accompanied a duration of more than five years.1 In the present family, all four patients examined had the same 24 CAG repeats in the CACNA1A gene in spite of phenotypic variability. Each patient with neuropathy or spasticity, however, exhibited a long disease duration, i.e., 40 or 12 years, respectively. Therefore, the disease duration might have influenced the phenotypic variability in our SCA6 patients. Further examinations are required to determine whether or not there is any genotype-phenotype correlation or some factors influence the phenotypic variability in SCA6.

The number of expanded CAG repeats in the CACNA1A gene is usually stable during transmission from a parent to an offspring, there being only a few exceptions.10 Interestingly, patient II-4 had 25 CAG repeats, the other six patients (II-2, II-8, III-7, III-9, III-13, and III-21) having 24 CAG repeats in this family. Unfortunately, we could not obtain direct evidence of intergenerational instability of CAG repeats because of the death of patient I-1. However, there may be intergenerational instability of the CAG repeats in the CACNA1A gene in this family.

In conclusion, the present study shows the intrafamilial clinical variability and worldwide distribution of SCA6.

 

Acknowledgment

 

The authors thank the family for participating in this study. This work was supported by a grant from the Research Committee for Ataxic Diseases (Y.T.) of the Ministry of Health, Labor, and Welfare, Japan.

 

References

 

1         Schöls L, Kruger R, Amoiridis G, Przuntek H, Epplen JT, Riess O. Spinocerebellar ataxia type 6: genotype and phenotype in German kindreds. J Neurol Neurosurg Psychiatry. 1998; 64: 67 – 73.

2         Takahashi H, Ishikawa K, Tsutsumi T, Fujigasaki H, Kawata A, Okiyama R, et al. A clinical and genetic study in a large cohort of patients with spinocerebellar ataxia type 6. J Hum Genet. 2004; 49: 256 – 264.

3         Zhuchenko O, Bailey J, Bonnen P, Ashizawa T, Stockton DW, Amos C, et al. Autosomal dominant cerebellar ataxia (SCA6) associated with small polyglutamine expansions in the alpha 1A-voltage-dependent calcium channel. Nat Genet. 1997; 15: 62 – 69.

4         Moseley ML, Benzow KA, Schut LJ, Bird TD, Gomez CM, Barkhaus PE, et al. Incidence of dominant spinocerebellar and Friedreich triplet repeats among 361 ataxia families. Neurology. 1998; 51: 1666 – 1671.

5         Silveira I, Miranda C, Guimaraes L, Moreira MC, Alonso I, Mendonca P, et al. Trinucleotide repeats in 202 families with ataxia: a small expanded (CAG)n allele at the SCA17 locus. Arch Neurol. 2002; 59: 623 – 629.

6         Bryer A, Krause A, Bill P, Davids V, Bryant D, Butler J, et al. The hereditary adult-onset ataxias in South Africa. J Neurol Sci. 2003; 216: 47 – 54.

7         Storey E, du Sart D, Shaw JH, Lorentzos P, Kelly L, McKinley-Gardner RJ, et al. Frequency of spinocerebellar ataxia types 1, 2, 3, 6, and 7 in Australian patients with spinocerebellar ataxia. Am J Med Genet. 2000; 95: 351 – 357.

8         Ishikawa K, Tanaka H, Saito M, Ohkoshi N, Fujita T, Yoshizawa K, et al. Japanese families with autosomal dominant pure cerebellar ataxia map to chromosome 19p13.1-p13.2 and are strongly associated with mild CAG expansions in the spinocerebellar ataxia type 6 gene in chromosome 19p13.1. Am J Hum Genet. 1997; 61: 336 – 346.

9         Takiyama Y, Sakoe K, Namekawa M, Soutome M, Esumi E, Ogawa T, et al. A Japanese family with spinocerebellar ataxia type 6 which includes three individuals homozygous for an expanded CAG repeat in the SCA6/CACNL1A4 gene. J Neurol Sci. 1998; 158: 141 – 147.

10      Shimazaki H, Takiyama Y, Sakoe K, Amaike M, Nagaki H, Namekawa M, et al. Meiotic instability of the CAG repeats in the SCA6/CACNA1A gene in two Japanese SCA6 families. J Neurol Sci. 2001; 185: 101 – 107.

 


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