Objective: Patients with spinocerebellar ataxia type 7 (SCA7) have progressive ataxia associated with pigmental macular degeneration, pyramidal and extrapyramidal signs and some of them have mental problems. SCA7 is one of the CAG trinuleotide expansion diseases. The length of CAG repeats of ATXN7 is reported to affect the symptoms of SCA7. We examined four Japanese patients with SCA7 in a family. We aimed to clarify the relation of clinical features and CAG repeat numbers in Japanese SCA7 patients. Intermediate CAG repeat expansion is thought to lead to abnormal repeat expansion. We think variation of repeat number of CAG repeats is rather small compared with other CAG repeats disease. We investigate the CAG repeats numbers in our SCA7 patients and normal population.

Background: Major genotypes of Japanese autosomal dominant cerebellar ataxia are SCA6, SCA3/MJD, SCA31 and DRPLA. SCA7 is very rare in Japan.

Methods: We took clinical examination for two SCA7 patients and examine the medical records for other two patients. We took peripheral blood and extracted DNA from 3 patients with SCA7 and 167 normal controls with informed consent. We did PCR with fluorescent labeled primer and fragment analysis to get the CAG repeat number of ATXN 7 for patients and controls. We investigate the CAG repeat numbers of SCA1, 2, 3, 6 and DRPLA gene for controls with the same method.

Results: The proband of this SCA7 progressed cerebellar ataxia in middle age. He had blurred vision at three years later and mental problem such as cenesthesic hallucination at 10 years after onset. His CAG repeats of ATXN7 gene was 41. One of his daughter with 120 CAG repeats occurred ataxia and visual disturbance at 2 years old and died at 4 with pneumonia. The age at onset of his another daughter with 42 repeats was almost same as her father. The mother of the proband occurred ataxia at about 70 and had no visual disturbance during 10 years illness. The range of SCA7 CAG repeats of controls was 7 to 14 and seventy-six percent of control alleles was 10 repeats. The variation of repeats was smaller than other SCAs.

Conclusions: SCA7 patients with small expansion of CAG repeats had only cerebellar ataxia at advanced age. We should do genetic examination and fundus examination to avoid the underdiagnosis of SCA7 in Japan. Variation of CAG repeat of ATXN7 is narrow than other SCAs. This might lead to low prevalence of SCA7 in Japan.

« Back to 2016 International Congress

MDS Abstracts - https://www.mdsabstracts.org/abstract/cag-repeats-number-of-atxn7-in-sca7-patients-and-normal-population-in-japan/