Autosomal Recessive Juvenile Parkinsonism (AR-JP): Genetic Diagnosis

Autosomal recessive juvenile parkinsonism (AR-JP) is a familial levodoparesponsive parkinsonism resulting from Lewy body negative degeneration of nigral neurons in the zona compacta of the substantia nigra (1 –4 ). The first proposal for a distinct clinical entity with recessively inherited parkinsonism was made in Japan and was termed “paralysis agitans with marked diurnal fluctuations of symptoms” (1 ). This syndrome was later designated as autosomal recessive form of juvenile parkinsonism (2 ). It was subsequently found to be linked to the 17-cM region on chromosome 6q25.2–27, and the locus was recently designated Park2 (3 ,5 ). Through the study of a patient who had homozygous microdeletion of the marker D6S305 (5 ), the responsible gene was identified by positional cloning and was designated parkin (6 ). Linkage and mutation analysis to date have shown that founders of mutations in this gene are multiple and widely distributed in the world (7 –13 ). Abnormalities in this gene, which are specific for AR-JP, include homozygous exonic deletions, small deletions, and point mutations. The presence of homozygous exonic deletions strengthens the notion that nigral neurodegeneration in AR-JP is caused by loss of function of the parkin protein.