 Early growth and nutrition, larger body size, and obesity may be environmental modifiers of genetic predisposition to HCM.Another potential health problem is spinal muscular atrophy (SMA), another genetically inherited disease which causes the loss of the spinal-cord neurons which activate the skeletal muscles of the trunk and limbs.Symptoms are normally seen within 3–4 months of age and result in muscle atrophy, muscle weakness, and a shortened lifespan.