Autosomal Dominant Disorders

AUTOSOMAL DOMINANT CEREBELLAR ATAXIA WITHOUT RETINAL DEGENERATION

Autosomal dominant cerebellar ataxias (ADCAs) without retinal degeneration comprise a heterogeneous group of dominantly inherited neurodegenerative diseases in which ataxia is the leading symptom. In most families, additional extracerebellar symptoms (saccade slowing, ophthalmoplegia, optic atrophy, pyramidal signs, amyotrophy, basal ganglia symptoms, dementia: ADCA-I) are present, whereas families with a pure cerebellar syndrome (ADCA-III) are less frequent. y

The genetic heterogeneity of ADCA has been established. In ADCA-I, the disease loci have been assigned to chromosome 6p (spinocerebellar ataxia type 1 [SCA1]), 12q (SCA2), 14q (SCA3), and 16q (SCA4). y y y y In an ADCA-III family with an almost pure cerebellar phenotype, a linkage with a marker on chromosome 11cen was demonstrated (SCA5). A novel locus, SCA6, has been identified on 19p (see T§b.!§...3.5..-2. ) [2Z]

Machado-Joseph disease (MJD) is a dominantly inherited ataxic disorder in which there is great phenotypical variation. MJD was first described in patients of Azorean descent. Later, the MJD phenotype was also observed in families of non-Azorean origin. Although MJD patients may have some clinical features, such as prominent eyes, severe dystonia, and amyotrophy, which are less frequently seen in North American and European ADCA families, there is no convincing clinical evidence to separate MJD from ADCA-I.y The gene locus of Japanese MJD families has been mapped to chromosome 14q, coincident with the localization of SCA3. Subsequent work has shown that the same mutation causes MJD in Japanese families and ADCA in European and North American SCA3 families. y

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