“What causes SMA? Chromosome 5 SMA is caused by a deficiency of a motor neuron protein called SMN, for “survival of motor neuron.” This protein, as its name implies, seems to be necessary for normal motor neuron function. Its deficiency is caused by genetic flaws (mutations) on chromosome 5 in a gene called SMN1.”
Spinal Muscular Atrophy | Muscular Dystrophy Association
https://www.mda.org/disease/spinal-muscular-atrophy