“Spinal Muscular Atrophy – SMA has generally been believed to affect as many as 10,000 to 25,000 children and adults in the United States, and therefore it is one of the most common rare diseases. One in 6,000 to one in 10,000 children are born with the disease. One in 40 to one in 50 people (approximately 6 million Americans) are carriers of the SMA gene. SMA is an autosomal recessive genetic disease, meaning that a person must have two copies of a defective gene to have the disease. SMA carriers do not exhibit SMA symptoms, but do carry a defective copy of the SMN1 gene. If both parents are carriers of the SMA gene, then each of their children has a 1 in 4 chance of having the disease. SMA has multiple forms which vary in severity.”

SMA Foundation (SMA Foundation | About SMA)