Spinal Muscular Atrophy (SMA) is a genetic disorder that affects muscle control. This condition happens when certain motor neurons in the spinal cord and brainstem are lost. This loss of motor neurons leads to weak and wasted muscles, affecting activities like walking, crawling, sitting up, and controlling head movement. In severe cases, it can also impact muscles used for breathing and swallowing.
In the following sections, we will explain the types of SMA, how it is diagnosed, and the available treatments in simpler terms.
Types of SMA
There are various types of SMA that differ in their characteristics, the severity of muscle weakness, and the age at which muscle problems appear.
Doctors categorize SMA into five types: type 0, type I, type II, type III, and type IV. Each type has different symptoms that help doctors understand the extent of the disorder.
Type 0 – Type 0 SMA is one of the most severe forms that affects babies before birth. Babies with type 0 SMA have severe breathing problems. They also show signs of severe muscle weakness, reduced muscle tone, and delays in developing age-appropriate motor skills.
Type I – Also known as Werdnig-Hoffman disease, this is another severe form of SMA that becomes evident at birth or within a few months. Affected infants experience delayed physical development and struggle to support their head or sit without assistance. Type I SMA children may have breathing and swallowing difficulties, which can lead to choking, reduced limb movements, tremors, muscle twitches, lack of reflexes, and severely reduced muscle tone.
Type II – Type II SMA often starts between 6 and 18 months of age. Children with this type can sit without support but need assistance getting into a sitting position. They can’t stand or walk independently.
Type III – Also called Kugelberg-Welander disease or juvenile SMA, this type has milder features that typically develop from early childhood to adolescence. Individuals with Type III SMA can stand and walk without help but have trouble climbing. It also causes an abnormal walking pattern, difficulty rising from a chair, and finger tremors.
Type IV – Type IV SMA usually appears after the age of 30 and results in mild to moderate muscle weakness, twitching, tremors, or mild breathing issues.
Diagnosing SMA
When doctors suspect SMA based on symptoms, they perform a thorough physical examination and review the patient’s family medical history. To confirm the diagnosis and rule out other conditions, specific tests are recommended.
Genetic Testing – SMA is linked to two genes, Survival Motor Neuron (SMN) and Neuronal Apoptosis Inhibitory Protein (NAIP). Genetic testing checks for defects or changes in these genes to help diagnose the disorder.
Electrodiagnostic Tests – These tests include nerve conduction studies and electromyography (EMG). Nerve conduction studies involve placing electrodes on the skin to stimulate sensory or motor nerves and measure electrical impulses. EMG uses a needle electrode to assess muscle bioelectrical activity, aiding in nerve damage diagnosis.
Muscle and Nerve Biopsy – Muscle biopsy, while less common, is used when other diagnostic methods fail. A small sample of muscle and nerve tissue is removed and examined for signs of SMA.
Treatments for SMA
Patients diagnosed with SMA receive various treatments, including medications, physical therapy, mobility aids, special diets, and respiratory support.
Medications – These medications target proteins in the central nervous system that might harm nerve cells.
Physical Therapy – Children with SMA receive physical therapy to learn special exercises that keep their muscles flexible and mobile.
Mobility Aids – Electric wheelchairs are provided to children with type I and II SMA who can’t stand or walk without assistance.
Nutrition – Children with type II SMA have special dietary needs due to difficulties in chewing and swallowing, so they follow a specific diet.
Respiratory Support – This includes breathing exercises, the use of breathing equipment, supplemental oxygen, and annual vaccinations.
