• Most cases of spinal muscular atrophy (SMA) are caused by changes to part of a chromosome called 5q, hence they are categorized as 5q SMA.
• Researchers have begun to discover that mutations in other genes can also cause SMA.
• A new study presented the case of a 13-year-old boy who developed SMA due to changes in a gene called ASAH1.

A recent study can help doctors understand less common genetic causes of SMA. The report, published in the May-June issue of the Journal of Medicine and Life, presents the case of a boy with SMA. This child has different gene changes than are normally seen in people with the condition.

Nineteen out of 20 people with SMA have changes in a gene called survival motor neuron 1 (SMN1). Normally, this gene is responsible for creating a protein called SMN, which is needed for the healthy functioning of motor neurons (the nerves that allow the brain and the muscles to communicate). In people with SMA, gene changes lead to low levels of SMN protein, fewer motor neurons, and muscle weakness.

Genes are located on chromosomes (long pieces of DNA). Because the SMN1 gene is located on part of a chromosome called 5q, doctors sometimes refer to SMA caused by changes in the SMN1 gene as 5q SMA. However, researchers have begun to discover cases of SMA caused by other genes. They call these cases non-5q SMA.

In the new study, researchers tell the story of a young boy with motor problems. The boy had difficulty moving his lower limbs for his entire life. When he was 4 years old, he underwent testing that showed that he might have a disease that affected his motor neurons. However, genetic testing showed that the boy did not have any mutations in the SMN1 gene.

When the child was 10 years old, he began to use a wheelchair. His muscle weakness became progressively worse. At the age of 13, he went to the hospital with severe breathing problems.

The researchers performed genetic testing for the boy on other genes besides SMN1. They found he had three different gene mutations in a gene called ASAH1. This gene makes an enzyme that helps recycle and create new ceramides — molecules that help make the protective covering on neurons. Changes in this gene can lead to SMA as well as another genetic disorder called Farber disease. The study authors found that the boy had symptoms of both conditions.

This study can help experts learn more about other gene changes that can lead to SMA. About 1 out of 20 people with SMA have mutations in other genes besides SMN1. Knowing which other gene changes to look for may help doctors more accurately diagnose SMA.