Spinal Muscular Atrophy (SMA)

What is SMA?

Spinal Muscular Atrophy (SMA) is a genetic disorder that affects approximately 1 out of every 10,000 people. Most cases of SMA occur when a segment of a gene called SMN1 is missing, resulting in the gene being unable to make protein. SMN1 is primarily responsible for making survival motor neuron (SMN) protein, which is required for maintaining normal, motor neuron function. Without enough SMN protein, motor neurons will degenerate, causing progressive loss of controlled muscle movement. There are different levels of SMA severity. Typically, the earlier the onset of the disease, the more severe the symptoms. SMA can affect a baby’s ability to swallow, breathe, sit, and walk. Without early treatment, SMA can also result in premature death.

How do newborn screening programs detect SMA?

In routine newborn screening, state public health laboratories use dried blood spots collected from a baby’s heel within the first 24-48 hours of birth to detect genetic disorders including SMA.

To detect SMA, laboratorians perform a test to determine if the gene segment that causes SMA is missing. If the SMN1 gene is found to be abnormal, either the public health laboratory or a clinical laboratory will do further studies to identify the number of copies of the SMN2 gene. SMN2 also produces SMN protein but in smaller quantities that will not compensate for the amount missing due to the abnormal SMN1. As a result, when a baby has more than three copies of SMN2, SMA will likely develop later in life and typically in a milder form.

Treatment for SMA

The U.S. Food and Drug Administration (FDA) has approved two drugs given by injection for SMA in newborns:  Spinrazapdf iconexternal icon® (nusinersen), and Zolgensmaexternal icon® (onasemnogene abeparvovec-xioi). Spinraza® adjusts the function of the SMN2 gene to produce more SMN protein and requires multiple treatments. In a single treatment, Zolgensma® replaces the non-functional SMN1 with a functional gene. For patients over two months old, FDA has approved a third drug that is given orally, Evrysdiexternal icon®(risdiplam), which also promotes SMN protein production by SMN2.

How CDC supports states in efforts to screen for SMA

The Newborn Screening and Molecular Biology Branch at CDC helps states implement and enhance the detection of SMA and improve the health and lives of newborns in a few key ways.

  • Ensuring the Accuracy of SMA Newborn Screening

The Newborn Screening Quality Assurance Program (NSQAP) offers dried blood spot materials that are similar to those collected from newborns with SMA. Public health laboratories routinely test the dried blood spot materials to ensure their methods continue to accurately identify babies with SMA.

  • Providing Technical Support

The Molecular Quality Improvement Program (MQIP) developed and validated a screening test that allows state public health laboratories to test for both SMA and Severe Combined Immunodeficiency (SCID) at the same time using a technique called real-time qPCR. It is a cost-effective and timely way for laboratories to screen for more than one condition simultaneously. As programs add SMA to their newborn screening panel, MQIP provides newborn screening laboratories with technical support and guidance for ongoing testing. MQIP also performs site visits to newborn screening laboratories and provides program-specific guidance for quality assurance and to maximize program performance.

  • Funding SMA Screening

CDC helps state public health laboratories add SMA to their screening panel by providing funding through cooperative agreements and technical support.

Page last reviewed: December 20, 2021