What is Spinal Muscular Atrophy?
Spinal Muscular Atrophy (SMA) is a genetic condition that causes muscles to weaken and waste away (atrophy). It affects roughly 1 in 10,000 newborns causing “floppy babies”, and about 1 in 50 people are asymptomatic carriers of the genetic mutation.
In a healthy body, motor neurons which are specialized nerve cells continuously send electrical signals telling muscles when to contract. In a person with SMA, these motor neurons break down and die. Without signal flow, muscles remain inactive, gradually shrinking and weakening over time.
The Genetic Cause: Missing Instructions
SMA is caused by a missing or mutated gene known as SMN1 (Survival Motor Neuron 1). This gene acts like an instruction manual for producing the SMN protein, which motor neurons desperately need to stay alive and healthy.
Humans also possess a “backup” gene called SMN2. However, SMN2 is inefficient, producing only about 10% of the functional SMN protein required by the body. How many copies of this backup gene a person has often determines the severity of their condition.
The Four Main Types of SMA
| Type | Onset Age | Typical Severity & Impact |
| Type 1 (Infantile) | 0 – 6 months | Severe weakness; babies struggle to sit independently, swallow, or breathe. |
| Type 2 | 6 – 18 months | Moderate weakness; children can sit unassisted but typically cannot stand or walk independently. |
| Type 3 (Juvenile) | Early childhood to teens | Mild to moderate weakness; individuals can walk but may have difficulties in running or climbing |
| Type 4 (Adult) | Adulthood (30+ years) | Mild; gradual weakness, mostly affecting hips, shoulders, and upper limbs. |
The Race Against Time: Breakthroughs in Treatment
Modern medicine has transformed SMA from a fatal childhood illness into a treatable condition. Today, advanced disease-modifying therapies, including oral medications (risdiplam) and gene therapy (onasemnogene abeparvovec) can target the underlying genetic defect.
The Golden Rule of SMA Treatment: Treatment stops the loss of remaining motor neurons, but it cannot restore those already lost. Treating an infant before or immediately after symptoms appear yields dramatically better developmental outcomes than treating a child years later.
Early diagnosis opens doors for families to seek early supportive care, such as respiratory therapy, tailored physical rehabilitation, and specialized nutrition, which significantly improves quality and length of life even while global access to disease-modifying therapies expands.
The Role of Newborn Genetic Screening for SMA Early Detection
Because dead motor neurons cannot be restored, early detection is critical. Modern newborn screening programs test infants’ SMN genes at birth, so treatment can begin before symptoms even start, allowing many children to hit normal developmental milestones like standing and walking. Give your baby the best start in life with NGI’s newborn genetic screening, enabling precise screening and early diagnosis in your child’s first days.
References:
Hurley, Dan. 2025. “Presymptomatic Treatment of Newborns With Spinal Muscle Atrophy Found Effective.” Neurology Today 25 (21). https://doi.org/10.1097/01.wnt.0001172324.08812.c9.
National Institute of Neurological Disorders and Stroke. 2023. “Spinal Muscular Atrophy | National Institute of Neurological Disorders and Stroke.” In Www.Ninds.Nih.Gov. https://www.ninds.nih.gov/health-information/disorders/spinal-muscular-atrophy.
Novartis Pharmaceuticals Corporation. n.d. “Presymptomatic SMA – SPR1NT Clinical Study Results.” In Zolgensma. Accessed August 4, 2026. https://www.zolgensma.com/zolgensma-studies/presymptomatic-study-results.
