Interestingly, as a dimer it reverses its function and becomes an ubiquitin-protein ligase resembling the E3 enzymes of the UPS.2 The UCHL1 gene gained special interest after it had been linked to a family with an autosomal dominant missense mutation (p.I93M) causing Parkinson's disease (PD).3 While this mutation seems to be very rare, another, more frequent UCHL1 polymorphism has been discovered in the course of a search for p.I93M mutants. The gene discussed is UCHL1; the disease is Parkinson disease.