Spinocerebellar Ataxia Type 10

SCA10 is a form of autosomal dominant cerebellar ataxia that was recently described in several kindreds of Mexican origin. The age of onset ranges from 10-49 years. Initial symptoms of the disease are gait unsteadiness, clumsiness and dysarthria. In a significant number of patients generalized motor seizures develop within a few years after onset of the ataxia. Some patients have reduced IQ. Findings on examination include nystagmus, dysarthria, gait and limb ataxia and nystagmus, with normal reflexes and motor function. Seizures respond to anticonvulsants. MR brain scans demonstrate cerebellar atrophy. There have been no pathological studies to date.

SCA10 is due to expansion of a pentanucleotide (ATTCT) repeat in intron 9 of a novel gene on chromosome 22q13 of unknown function. Normal ATTCT repeats range from 10 to 22 ATTCT units. The expansions of the ATTCT repeat, which have not been accurately sized, are massive, up to 22.5 KB longer than the normal alleles. The diagnosis of SCA10 is established by the demonstration of expansion in one ATTCT repeat alleles in the SCA10 locus greater than 800 repeats in an ataxia patient. Patients with intermediate expansions of 30-799 repeats would also be candidates for a possible diagnosis of SCA10 and a more detailed examination of the kindred would be appropriate.