DNA marker studies show that Machado Joseph disease is not an allele of the Huntington disease locus

The gene for Machado-Joseph disease maps to human chromosome 14q

Machado-Joseph disease (MJD) is an autosomal dominant, multisystem neurodegenerative disorder involving predominantly cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems. Although it was first reported in families of Portuguese-Azorean descent, MJD has also been described in non-Azorean families from various countries, being one of the most common hereditary spinocerebellar degenerations. With the use of highly polymorphic microsatellite DNA polymorphisms, we have assigned the gene for MJD to the long arm of chromosome 14 (14q24.3-q32) by genetic linkage to microsatellite loci D14S55 and D14S48 (multipoint lod score Zmax = 9.719).

The Machado-Joseph disease locus is different from the spinocerebellar ataxia locus (SCA1)

Machado-Joseph disease (MJD) is an autosomal dominant neurodegenerative spinocerebellar ataxia that has been described primarily in families of Azorean or Portuguese descent. MJD and chromosome 6p-linked spinocerebellar ataxia (SCA1) are difficult to differentiate clinically, and it has been suggested that they may be allelic variants of the same disorder. We have tested MJD families for linkage to six DNA sequence polymorphisms located on chromosome 6p, including the highly informative dinucleotide repeat, D6S89. Seventeen centimorgans telomeric to and 41 cM centromeric to D6S89, a region that includes the SCA1 locus reported to be within 3 cM of D6S89, have been excluded. These data provide conclusive evidence that MJD and SCA1 are nonallelic.