Spinal muscular atrophy (SMA) is a heritable disease characterized by the loss of lower motor neurons — the nerve cells that carry electrical signals from the brain to the voluntary muscles to control their movement. Motor neurons control the movement of the arms and legs, hands and feet, chest, face, throat, and tongue. The loss of these neurons leads to muscle weakness and problems with walking, breathing, and swallowing.

Inheritance of SMA

Everyone has two copies of each gene, one inherited from their mother, and the other inherited from their father. SMA is inherited in an autosomal recessive manner. This means that it only develops if a person inherits two faulty copies of the disease-causing gene.

If one parent has a single copy of the disease-causing mutation, they have a 1 in 2 chance of passing that gene on to their children. But a child only develops the disease if both parents carry a copy of the disease-causing gene and pass it to the child. In these cases, a couple has a 1 in 4 chance of having a child affected by SMA.

What is genetic counseling?

People who have a family member with SMA may wish to speak with a genetic counselor about their probability of being a carrier of the disease. They may also want to be tested to see whether they actually have a copy of the disease-causing gene and could pass it on to their children.

Patients diagnosed with SMA will work with a genetic counselor to understand the results of any genetic tests as well as the type of SMA they have, and what they can expect as the disease progresses.

A genetic counselor can also work with patients to plot their family tree and determine whether other family members may have inherited the disease.

How to find a genetic counselor

In the U.S. and Canada, patients can search for genetic counselors in their region on the National Society of Genetic Counselors website.

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SMA News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.