FAMILIAL spastic paraplegia was first reported by Seeligmüller,1 and many additional cases have since been reported (see reviews by Rhein,2 Paskind and Stone,3 and Bell and Carmichael.4 Although the diagnosis is commonly made in patients with evidence of pyramidal tract disease beginning in the lower extremities, the disease is frequently more extensive and may progress to involve the arms as well as cranial nerves. Some difference of opinion exists4,5 regarding the full range of clinical manifestations of spastic paraplegia, but families have been reported with mental defect, optic atrophy, nystagmus, ataxia, seizures, rigidity, muscle atrophy, kyphosis, pes cavus, and cardiac conduction defects. The reported families probably comprise a heterogeneous group of disorders with somewhat similar clinical features, and as yet no pathological or biochemical distinctions are possible. On genetic grounds, however, at least three types must exist: one genetic defect produces dominant spastic paraplegia,4