[Pseudodominant inheritance of spinal muscular atrophy--father and son suffering from SMA]

Spinal muscular atrophy (SMA) is an autosomal recessive hereditary disorder caused by mutations of the SMN1 gene. Because of the autosomal recessive type of transmission, the genetic risk of the disease in the following generations is small and is estimated to be about 1%. Here we present a case report of a father and son suffering from SMA. The father is affected with a mild form of SMA, with onset at about 13 years of age. The son suffers from SMA type 2, with onset at about 13 months of age. In both father and son, genetic analysis showed biallelic deletion of exons 7 and 8 in the SMN1 gene. The boy's mother is a carrier of the deletion at the SMA locus. Quantitative analysis revealed one copy of the SMN1 gene.