Frank, an SMA parent, describes the genetics of SMA

Frank, an SMA parent, describes the genetics of SMA

What is SMA?

Spinal Muscular Atrophy (SMA) is an inherited disease that affects approximately 1 in 10,000 infants born in the U.S. each year. There are four types of SMA, based on the degree of symptoms, with SMA Type I being the most severe.

Cause and Inheritance

SMA is caused by an alteration in the SMN1 gene, which results in reduced levels of a protein called Survival Motor Neuron (SMN). The SMN protein is critical to the survival of nerve cells in the spinal cord responsible for muscle contraction. When these protein levels are reduced, the muscles do not function properly and become smaller and weaker (“atrophy”). SMA is an autosomal recessive disease, meaning that a person must have two copies of an altered SMN1 gene to have the disease.

  • Dr. De Vivo provides an overview of SMA and describes the four SMA types
  • Dr. Sumner explains the cause of SMA and the two genes, SMN1 and SMN2
  • Frank, an SMA parent, describes the genetics of SMA
  • An animation introduces DNA and the pattern of inheritance for SMA
  • Dr. Sumner describes how SMA is inherited
  • Dr. Sumner explains how the number of copies of the SMN2 gene may influence disease severity


Children with SMA generally appear normal at birth, with symptoms developing as early as a few months after birth. A diagnosis of SMA is usually confirmed by a genetic test to identify a mutation in the SMN1 gene.

  • Dr. De Vivo discusses the diagnosis of SMA
  • James talks of having a child with very severe Type I SMA
  • Esther and Frank talk about the diagnosis of their daughter, Maeve
  • Ron and Debbie recall their son Dylan’s diagnosis with Type II SMA
  • Steve remembers his early experiences with SMA
  • Dr. Sumner describes family planning options for parents who have a child with SMA