The neurophysiological patterns in patients with a POLG mutation were as follows: unobtainable sensory responses and normal motor studies in three patients; non-length dependent, predominantly sensory, axonal neuropathy with distal active and chronic neurogenic changes on EMG in two patients; and length-dependent, sensory or sensorimotor axonal neuropathy in three patients, one of them with mild slowing of sensory and motor conduction velocities. The gene discussed is POLG; the disease is axonal neuropathy.