Molecular genetic study of a childhood form of spinal muscular atrophy

Molecular genetic studies were performed in 28 cases of childhood-onset spi nal muscular atrophy (24 unrelated families). This consisted of type 1 (sev ere) (n = 5), type 2 (intermediate form) (n = 8), and type 3 (mild) (n = 15 ). Deletion of exons 7 and 8 of the SMNt gene was found in 100%, 100%, and 93%, respectively, in type 1, 2, and 3 spinal muscular atrophy. Deletion of exons 5 and 6 of the NAIP gene was found in 3 of 5 (60%) of type 1 and non e of the type 2 and 3 cases. None of the 32 asymptomatic relatives had homo zygous deletions in the SMNt and NAIP genes. Thus, the role of the NAIP gen e needs to be specifically defined in spinal muscular atrophy. In a suspect ed case of spinal muscular atrophy, deletion of the SMNt gene is a useful l aboratory marker for confirmation of the diagnosis.