LOF mutations in RAB39B were identified as a cause of X-linked recessive (XLR) early-onset parkinsonism (EOP) in 2014 through linkage analysis in three Australian brothers presenting intellectual disability (ID) with EOP, and confirmed via linkage analysis and direct RAB39B sequencing in a Wisconsin family with 13 males presenting a similar phenotype [44]. The gene discussed is RAB39B; the disease is Intellectual disability.