A study of environmental factors in relation to fatal infantile spinal muscular atrophy (SMA type I). An analysis of birth order and parental age effects, social class, seasonal influence, and clustering in time and place.

Major studies of the childhood spinal muscular atrophies have suggested that environmentally-produced phenocopies might occur, and that environmental factors might be important in some clinical features of these diseases. A formal analysis of some possible intra-uterine and post-natal influences has been undertaken in 78 index cases (72 families) of acute infantile SMA (acute Werdnig-Hoffmann disease; SMA Type I). There is no evidence to suggest that social class, parental age, birth order, or season of birth influences this disease or that clustering in time and place occurs.