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Machado Joseph disease(MJD)is an autosomal dominantly inherited neurodegenerative disorder primarily affecting the motor system.It can be divided into three phenotypes based on the variable combinations of a range of clinical symptoms including pyramidal or extrapyramidal features, cerebellar deficits,and distal muscle atrophy.MJD is thought to be caused by mutation of a single gene which has recently been mapped,using genetic linkage analysis,to a 29cM region on chromosome 14q24.3-q32 in five Japanese families.A second disorder,spinocerebellar ataxia type 3(SCA3), which has clinical symptoms similar to MJD,has also been linked to the same region of chromosome 14q in two French families.In addition,we show that this 11cM interal maps within the 15 cM interal containing the SCA3 locus,suggesting that these diseases are allelic. |
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