LRRK2 and Parkinson disease: Although it is possible that the association of low B12 with more rapid impairment of ambulatory capacity is mediated by its known role supporting central and peripheral nervous system myelination, recent studies have shown that B12 inhibits α‐synuclein fibrillogenesis3 and that B12 allosterically modulates leucine‐rich repeat kinase 2 (LRRK2),4 an enzyme implicated in PD pathogenesis, raising a disease specific mechanism of action.