[Genetics of child spinal amyotrophy : existence of 2 autosomal recessive forms].

An analysis of within sibship resemblances in age of onset of symptoms and age of death (or at last examination) was made in families affected with infantile spinal muscular atrophy. The observed correlation coefficients, 0.52 and 0.75, favor the existence of a least two different mutant genes for the disease. In 63 families, the disease was of the acute infantile form and in 71 families it was of the chronic form. Both forms show autosomal recessive transmission.