ABSTRACT
Longer disease durations of 30 years or over are observed only in late-onset patients. In Spinocerebellar Ataxia Type 7 (SCA7), anticipation is characterized by both earlier onset and more rapid disease progression in successive generations. The strong anticipation, particularly marked in SCA7, that was explained in other neurodegenerative disorders by unstable sequences, led several authors to postulate that a CAG expansion might be involved in this disease. The SCA7 transcript is expressed at the same level in the retina and all central nervous system structures tested, except the cerebellum where expression is higher. The size of the largest expansion and the degree of gonadal instability in SCA7 are greater than those observed in any of the seven known neurodegenerative diseases caused by translated CAG repeat expansions. The SCA7 region is characterized by a high level of meiotic recombination and a large discrepancy between the estimated genetic and physical distances.
