Allele-specific amplification for the diagnosis of autosomal recessive spinal muscular atrophy

The SMN1 gene is homozygously deleted for at least exon 7, interrupted or c onverted to a non-functional telomeric copy in most cases of proximal spina l muscular atrophies. The presence of a pseudogene hampers direct detection of the exon 7 deletion. We describe a method for the detection of the of e xon 7 deletion, based on the amplification refractory mutation system (ARMS ), in a multiplex PCR with fluorescent-labelled primers. The gene and pseud ogene amplification products differ in the dye bound and in their size, whi ch allows distinction of both products on electrophoresis. The pseudogene i s used as an internal control, and this method gives a clear and specific p attern for the patients. Amplification is achieved with 30 cycles, and spec ificity is retained up to 40 cycles.