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. The gene discussed is SMN1; the disease is spinal muscular atrophy.