Spinal Muscular Atrophy (SMA) is a hereditary disease present from birth that affects the motor neurons located in the anterior horn of the spinal cord. The prevalence of genetically inherited Spinal Muscular Atrophy (SMA) is approximately 1-2 per 10,000.

What is Spinal Muscular Atrophy (SMA)?
In SMA, there is no response to the neural stimulus that comes from the brain to the anterior horn cells of the spinal cord, which are responsible for the voluntary contraction of muscles. This is because of a genetic dysfunction in the motor anterior horn cells. Therefore, since these nerves do not send signals to the peripheral muscles, the muscles cannot contract voluntarily and begin to atrophy (waste away). All arm and leg muscles, the trunk, and some respiratory muscles are affected by this disease.

What Causes Spinal Muscular Atrophy (SMA)?
SMA, commonly known as “floppy baby syndrome,” is caused by a mutation in the motor neuron gene (SMA gene). In healthy individuals, the motor neuron gene produces a critical protein necessary for the proper functioning of nerves that control muscles. This protein ensures that the nerves remain strong and transmit commands from the brain. However, if this protein cannot be synthesized, degeneration and damage occur in the motor neurons. As a result, no signals reach the muscles.

The primary characteristic of all SMA types is muscle weakness accompanied by muscle wasting.

How Many Types of SMA Are There?
SMA is classified into 4 types based on the age of onset and clinical symptoms. The earlier the symptoms appear, the more severe the disease course. Type 1 SMA, which manifests before 6 months of age, is the most severe form.

• Type 1 SMA is also called hypotonic infant syndrome and is the most severe type. Affected infants show decreased movement, lack head control, and cannot sit unsupported. Although there may be no movement in the arms and legs, eye contact and hearing are normal. Type 1 SMA is one of the leading causes of infant mortality worldwide. Feeding and swallowing difficulties are common, and respiratory muscles are affected, leading to frequent respiratory infections. Lung capacity gradually decreases, and affected infants often require mechanical ventilation. Prognosis is poor.
• Type 2 SMA is usually seen between 6-18 months of age. Babies who initially develop normally then lag or regress compared to peers. These children have head control and can sit independently but cannot move from lying down to sitting position by themselves. They never stand or walk unsupported. Frequent respiratory infections and a high risk of spinal curvature (scoliosis) are common. This is a relatively severe form.
• Type 3 SMA begins after 18 months of age and progresses more slowly. Symptoms such as muscle weakness causing difficulty walking, frequent falls, and inability to climb stairs appear at any time until adolescence. These patients can stand and walk, and respiratory muscles are not affected. Scoliosis is somewhat more common in this group. They may need wheelchairs in later years.
• Type 4 SMA occurs in adulthood and has a good prognosis.

What Are the Symptoms of SMA?
Symptoms vary according to the age of onset and can differ from person to person. General symptoms include:

• Muscle weakness and loss of motor skills leading to delayed motor development. Weakness is generally symmetrical and often affects proximal muscles such as those around the shoulders and hips. Leg weakness is more pronounced than arm weakness.
• Delayed motor function compared to peers,
• Frequent falls, difficulty climbing stairs, standing, and walking,
• Hand tremors, tongue fasciculations,
• Decreased or absent deep tendon reflexes (sensory function remains intact),
• Feeding difficulties and swallowing problems, increasing the risk of aspiration,
• Inability to control head and trunk.

Diagnosis is made by genetic testing and electromyography (EMG). Genetic analysis detects anomalies in the SMN (survival motor neuron) gene located on the long arm of chromosome 5.

What Are the Treatment Methods for SMA?
Extensive research is ongoing for SMA treatment. The first drug approved by the FDA in 2016, SPINRAZA, is still used in children and can reduce or even halt disease progression.

In addition to drug therapy, rehabilitation programs have very beneficial and positive effects. The goals of rehabilitation include:

• Preserving the current condition and delaying deterioration as much as possible,
• Increasing or maintaining the child’s independence,
• Reducing the family’s caregiving burden,
• Preventing joint deformities,
• Preserving muscles,
• Managing respiratory complications,
• Ensuring social participation and quality of life.

Since SMA affects not only the musculoskeletal system but also causes many secondary problems, treatment principles should be holistic and multidisciplinary, and each patient should be treated individually.

Due to the effects of SMA, orthoses may be needed to prevent problems arising from muscle weakness. Also, mobility aids such as walkers and wheelchairs appropriate to the child’s functional status are recommended to support independence.

Education of the family about the disease and the importance of stretching and strengthening exercises to protect joints and muscles should not be overlooked.

The first step in SMA rehabilitation is to evaluate the patient’s current functional status, which should be repeated every 3-6 months because the functional status of a growing child changes continuously. Despite growth, widespread muscle weakness negatively impacts bones and tendons, causing developmental disorders in bones. Poorly developed hip joints are a common finding in SMA cases, with bilateral hip dislocation frequently observed.

Joints in SMA patients tend to be very loose. In the early stages, joint range of motion may exceed normal limits, which contributes to increased spinal scoliosis. Muscle weakness, joint laxity, limited joint motion, and growth-related changes in the arms and legs are the main factors affecting function in SMA patients.

How is Respiratory Physiotherapy Applied in SMA?
Weakness of respiratory muscles in SMA reduces lung ventilation, leading to frequent lung infections and diseases. Weakness of cough-related muscles makes secretion clearance difficult. Children with widespread muscle weakness have a high risk of aspiration.

Small oral feeds, use of straws, keeping the head upright during feeding, chin support, and feeding in small and frequent amounts help reduce aspiration risk.

From an early stage, increasing muscle strength, preserving chest wall flexibility, improving range of motion, and enhancing physical functions are important. Physiotherapists should teach appropriate positions for comfortable breathing.

Along with positioning, various drainage methods help clear lung secretions. Measures to prevent aspiration through proper postural drainage must be taken, and families should be trained accordingly.