Early infantile form of spinal muscular atrophy (Werdnig-Hoffmann disease) with prolonged survival.

According to several previously used classification systems, spinal muscular atrophy (SMA) type I has been characterised by an early onset (< 6 months), severe course (patients are never able to sit without support) and fatal prognosis (death before 2-4 years). We report 36 out of 349 SMA type I patients (10%) who had an onset before 6 months and never learnt to sit but survived at least beyond their fifth birthday, in spite of total immobility and frequent respiratory infections. These data support a classification avoiding age at death as a criterion. In the subgroup of type I with prolonged survival, there was no difference in life span between those individuals who had an onset of disease at birth or before and those with symptoms starting after 3 months. Life span may be related to the ability to withstand repeated respiratory insult, as several of the sibships with children affected by similar neuromuscular compromise showed discordant ages at death. "Chronic" SMA I and SMA II may represent overlapping phenotypes as our index patients with SMA I had a sib with SMA.