Homozygous deletion or mutation of SMN1 coupled with a single nucleotide substitution at position 6 of exon 7 (C6T) of SMN2 is responsible for spinal muscular atrophy (SMA)4, the most common genetic cause of infant death with a frequency of 1 in ~10,000 births5. Here, SMN2 is linked to spinal muscular atrophy.