PRKN and Parkinson disease: In addition, PRKN variants are the most common cause of early-onset PD (age of onset ≤ 20 years) [26] accounting for 42% of the familial early-onset PD cases [27] and the majority of PRKN-related PD patients with disease onset before 20 years of age carry bi-allelic PRKN variants [28].