A COLLABORATIVE STUDY ON THE NATURAL-HISTORY OF CHILDHOOD AND JUVENILE-ONSET PROXIMAL SPINAL MUSCULAR-ATROPHY (TYPE-II AND TYPE-III SMA) - 569 PATIENTS

We analyzed clinical data of 569 patients in two combined series with childhood and juvenile proximal SMA, This cohort included only patient s who had achieved the ability to sit unaided (type II and III SMA). T he survival rate among 240 type II patients (who sat but never walked) was 98.5% at 5 years and 68.5% at 25 years. SMA III (n = 329) (those who walked and had symptoms before age 30 years) was subdivided into t hose with an onset before and after age 3 years (type IIIa, n = 195; S MA IIIb, n = 134). In patients with SMA III, life expectancy is not si gnificantly less than a normal population. The probabilities of being able to walk at 10 years after onset was 70.3%, and at 40 years, 22.0% in SMA IIIa. For SMA IIIb, 96.7% were walking 10 years after onset an d 58.7% at 40 years. The subdivision of type III SMA was justified by the probability of being ambulatory depending on age at onset; the pro gnosis differed for those with onset before or after age 3 years. The data provide a reliable basis of the natural history of proximal SMA a nd support a classification system that is based primarily on age at o nset and the achievement of motor milestones. (C) 1997 Elsevier Scienc e B.V.