セキズイ ショウノウ ヘンセイショウ ノ イデンシ イジョウ
Genetic abnormalities in spinocerebellar degeration
Spinocerebellar degeration （SCD） is a neurogenerative disorder. The cardinal signs of SCD include cerebellar and spinal ataxia, extrapyramidal signs, dysautonomia, pyramidal signs, mental signs, involuntary movement. In Japan, about ３０％ of SCA cases are hereditary in nature. Recently, several forms of inherited SCD have been reported, and can be devided into four groups, three of which show autosomal dominant inheritance. Group Ⅰ : This group is caused by expansion of CAG repeats encoding polyglutamine streches, and includes SCA１，２，３ （Machado-Joseph disease）, SCA７，SCA１２，dentatorubral-pallidoluysian atrophy. The number of CAG repeats correlates with the age at onset and severity of symptoms. The expanded CAG repeats become unstable during parent-offspring transmission. Group Ⅱ SCA６）：This is caused by a mutation involving mild expansion of CAG repeats in the gene encoding the voltage-dependent Ca channel alpha１A subunit （CACNA1 A）. The pathogenic CAG repeats are fewer than in Group I and stable during parent-offspring transmission. Group Ⅲ : This group is not caused by expansion of CAG repeats, and includes SCA８ （CTG expansion）, SCA１０ （ATTCT expansion）, and SCA１４ （point mutation). Group Ⅳ : This group shows sutosomal recessive inheritance, and includes Freidreich’s ataxia, early-onset ataxia with ocular motor apraxia and hypoalbuminemia, and ataxia with isolated vitamin E deficiency.
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