STRASBURG, PA- A natural history study has provided the first comprehensive clinical description of spinal muscular atrophy (SMA) within the Amish and Mennonite communities and correlates ancestral chromosome 5 haplotypes and SMN2 copy number with disease severity. SMA is a devastating genetic disease that affects the motor neurons that control movement, eating, and breathing. It represents the leading genetic cause of infant death worldwide, with an incidence of approximately 1 per 10,000 newborns worldwide and as many as 1 per 2,800 babies of Mennonite descent. The observations were conducted within a population-specific framework to elucidate subtle differences in disease expression and the subsequent impact of disease-modifying therapies administered early in life. Forty-two Mennonite and fourteen Amish patients with SMA were included in the study by practitioners and researchers at the Clinic for Special Children in Strasburg, PA. The study is published online today in PLOS ONE.