What causes SMA?
SMA is a genetic disease. In order for a child to be affected by SMA, both parents must be carriers of the abnormal gene and both must pass this abnormal gene on to their child. If both parents are carriers the likelihood of a child inheriting the disorder is 25%, or 1 in 4. If both parents are carriers of SMA the likelihood of a child who is a carrier of SMA is 50%, or 2 in 4. If both parents are carriers of SMA the likelihood of a child with who is neither a carrier of SMA nor affected with SMA is 25%, or 1 in 4.
