In demyelinating forms of hereditary motor and sensory neuropathy (HMSN), also known as CMT1 or CMT4, associated genes include GDAP1, MTMR2, SBF2, NDRG1, EGR2, SH3TC2, PRX, FGD4, PMP22, GJB1, MPZ, MFN2, MED25, and FIG4. The gene discussed is FGD4; the disease is hereditary motor and sensory neuropathy.