the infantile spinal muscular atrophies (sma) are hereditary neuromuscular diseases characterized by degenerated alfa-motoneurons of the anterior spinal marrow horn. werdning-hoffman disease, type 1 sma, is the most serious affection being transmitted as an autosomal recessive character, so those affected may die from respiratory failures in the first year of life. this paper presents a cuban family with two kids who suffer from type-1 sma; the molecular analysis carried out in one of them identified two parental chromosomes responsible for the disease. also, a deletion of both copies of smn gene (exon 8) and naip gene (exon 5) were discovered in this patient. these findings showed the usefulness of this kind of studies with a view to making a prenatal diagnosis of werdning-hoffman disease.