Patients with three copies of SMN2 may develop SMA types 1, 2 or 3, but the presence of three copies is 54% predictive of intermediate-severity SMA type 2 with onset between 7 months and 18 months of age, 15% predictive of type 1 and 31% predictive of the milder type 3 phenotype3. The gene discussed is SMN2; the disease is spinal muscular atrophy, type II.