Distal spinal muscular atrophy. A clinical and genetic study of 8 kindreds.

Twelve patients (8 kindreds) with distal SMA are described, and an analysis presented of their clinical and genetic features. Distal SMA accounted for 10% of all patients with SMA in a total population survey of this disease in North-East England. The parental consanguinity rate is high, occurring in 3 of the 8 kindreds reported; the sex ratio was 1.0; the segregation ratio of sibs did not differ from 0.25. Intrafamilial concordance for clinical features of the disease is high. This current data is consistent with a suggested aetiology of two separate autosomal recessive genes. Clinical features are discussed and a review of the literature presented. The disease is only slowly progressive, but one of the genetic types may present with infantile or early juvenile onset; there is no evidence that it shortens life. 50% of cases did not have a normal gait after 4 years of age; 50% could not run after 17 years of age; and 50% could not walk unaided after 28 years of age. Details of prognosis, and principles of genetic counselling in this disease are discussed.