Dopa‐responsive parkinsonism phenotype of Machado‐Joseph disease: Confirmation of 14q CAG expansion

Abstract The subtype IV of Machado‐Joseph disease (MJD), characterized by parkinsonism variably combined with ataxia, distal atrophy, and sensory loss, has been all but ignored in recent reports of MJD, including those describing the molecular biologic substrate of the disease. We have demonstrated expansion of the CAG trinucleotide repeat of the MJD1 gene located on chromosome 14q32.1 in 2 patients of Azorean descent who presented with levodopa‐responsive atypical parkinsonism. Previous publications have documented the presence of this expanded repeat in the other more common MJD phenotypes (I‐III). To our knowledge, this is the first molecular biologic confirmation of the presence of the MJD1 gene in the subtype IV phenotype. Patients presenting with parkinsonism and peripheral neuropathy should be screened for this genetic defect.