PRKN and Parkinson disease: Although bi-allelic mutations in Parkin typically have a high penetrance rate27, 28, we have previously identified an unusual case of a homozygous Parkin mutation carrier who has not developed PD by her eighth decade despite Parkin deficiency (“asymptomatic carrier” hereafter), whereas her daughter who was a compound heterozygote presented with typical early-onset PD (“Parkin MT1” hereafter)29.