Parkin disease is usually autosomal recessive; however, two studies have shown that asymptomatic heterozygotes have nigrostriatal dysfunction and even manifest subtle extrapyramidal signs. The authors used ¹⁸F-dopa PET to study 13 asymptomatic parkin heterozygotes and found a significant reduction of ¹⁸F-dopa uptake in caudate, putamen, ventral, and dorsal midbrain compared with control subjects. Four had subtle extrapyramidal signs. Parkin heterozygosity is a risk factor for nigrostriatal dysfunction and in some may contribute to late-onset Parkinson disease.