The Biology of Gene Mutation

Spinal muscular atrophy is a genetic disease. What does that mean?

A genetic disease is, quite simply, a disease caused by a mutation in a gene. When a gene is damaged, it can mutate. That means that the gene carries a different message to the proteins in the human body. If the new message causes a certain protein to change or to stop working, all of the cells containing that protein will also malfunction. And the result can be a genetic disease.

Most genes come in pairs -- one received from the mother, one from the father. If the child inherits mutated genes, the child can be at risk for a genetic disease.

Here, a primer on various ways genetic disorders can be inherited:

Autosomal Dominant Mutations: This mutation will put someone at risk for the disease if one gene in a pair is mutated.

If one parent carries a copy of the gene mutation, there will be a 50 percent chance that each child inherits the disorder and a 50 percent chance that each child has two normal genes. So in this case, all it takes is one parent to pass on the disease.

Autosomal Recessive Mutations: Both the mother and father must carry a copy of the gene mutation in order for their children to have the trait. There is a 25 percent chance that each child they have will have the disorder, a 50 percent chance that each child will carry the mutation but not have the disorder, and a 25 percent chance that the child will have two normal genes.

X-linked Recessive: Mutations on the X chromosome (one of the sex chromosomes) occur more often in males, because they only have one X chromosome. (So if they inherit a copy from either parent, they will have the disorder.) Females must inherit copies from both parents to have the trait, but only need a copy from one parent to carry the trait.

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