These two phenotypic presentations seem to correlate with residual phosphatase activity: variants leading to (nearly) complete loss of dual phosphatase activity lead to the first phenotype, while loss of dephosphorylation activity limited to the Sac1 domain leads to Parkinsonism with onset in early adulthood and mild increase in seizure susceptibility [124]. The gene discussed is SACM1L; the disease is Parkinsonism.