Spinocerebellar ataxia type 20.
Spinocerebellar ataxia type 20 (SCA20) was reported in 2004 in a single Australian Anglo-Celtic pedigree. The phenotype is distinctive, with palatal tremor, and hypermetric saccades, and early dentate (but not pallidal) calcification in the absence of abnormalities of calcium metabolism. Dysarthria, rather than gait ataxia, was the initial symptom in most, and was typically conjoined with dysphonia, clinically resembling adductor spasmodic dysphonia. The onset of these speech abnormalities was abrupt in some cases. MRI scanning showed mild to moderate pancerebellar atrophy with dentate calcification, with olivary pseudohypertrophy in some cases, in the absence of other brainstem or cerebral changes. Nerve conduction studies were normal. Progression appeared to be slow. SCA20 is probably rare, as despite the distinctive phenotype, only this one pedigree has been described. The locus mapped to the pericentromeric region of chromosome 11 with a LOD score of 4.47, and its candidate region overlaps that of SCA5. It seems probable that these two SCAs may be separate genetic entities, on the basis of their divergent clinical features, but formal proof awaits discovery of one or both responsible genes.
Storey
Elsdon
E
Department of Medicine (Neurosciences), Alfred Hospital Campus of Monash University, Melbourne, Australia. elsdon.storey@med.monash.edu.au
Knight
Melanie A
MA
Forrest
Susan M
SM
Gardner
R J McKinlay
RJ
D000328:Adult; D017668:Age of Onset; D001921:Brain / Q000473:pathology; D002874:Chromosome Mapping; D002880:Chromosomes, Human, Pair 11; D005260:Female; D005799:Genes, Dominant; D008040:Genetic Linkage; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D020754:Spinocerebellar Ataxias / Q000145:classification* / Q000235:genetics* / Q000473:pathology / Q000503:physiopathology; D019680:Trinucleotide Repeat Expansion