Distal spinal muscular atrophy is a type of spinal muscular atrophy that primarily affects your hands and feet along with your lower arms and legs. Treatments focus on relieving symptoms.

A genetic disorder that can result in muscle weakness and trouble walking, breathing, and eating is known as spinal muscular atrophy (SMA). The distal type of SMA can affect your arms, legs, hands, and feet.

While no cure currently exists for individuals with distal SMA, there are treatments that can help with related symptoms.

A doctor can help you to develop an individualized treatment plan if you believe you have distal SMA or another form of SMA. Being aware of the causes and symptoms of SMA can help you to get the appropriate assistance faster.

SMA is a genetic disorder known for muscle weakness and the deterioration of muscles.

Although muscle deterioration related to SMA is frequently worse close to your core, distal SMA is a form of SMA that mainly affects your hands and feet along with your lower arms and legs.

Forms of SMA can be classified based on the age an your symptoms generally start:

  • Type 1 (babies 6 months or younger): In addition to reduced muscle tone and potential skeletal issues, individuals with type 1 SMA may have trouble breathing or feeding.
  • Type 2 (babies or toddlers between 7 and 18 months old): Individuals with type 2 SMA may be able to sit without support but not stand or walk. They may have trouble breathing or coughing.
  • Type 3 (children older than 18 months up until early adulthood): Although they may be able to walk, individuals with type 3 SMA may have difficulties with balance and shaky limbs. They may have difficulty getting up from a seated position and lose their ability to walk over time.
  • Type 4 (adult onset): Weakness may be present in the hands and feet of individuals with type 4 SMA. They may also have shaking or twitching muscles. Although individuals may eventually lose the ability to walk, individuals with type 4 SMA don’t tend to have difficulties with breathing and swallowing.

Symptoms of distal SMA include:

  • difficulty walking
  • trembling or shaking muscles
  • weakness or low muscle tone in your arms and legs

Other common symptoms of SMA are:

  • bone and joint conditions, including scoliosis
  • swallowing difficulties
  • breathing difficulties

SMA does not typically cause cognitive impairments or learning disabilities.

SMA is usually caused by mutations to the SMN1 gene. Differences in the extent to which people experience SMA are often attributed to the number of copies of the SMN2 gene they have.

The SMN protein is produced by the SMN1 and SMN2 genes. It plays an important role in maintaining motor neurons. These neurons transmit signals between your spinal cord and your brain, facilitating the movement of your muscles.

Individuals with SMA have a shortage of SMN protein, which leads to the destruction of motor neurons. Without these motor neurons, individuals can experience the lack of muscle control characteristic of SMA. When individuals have more copies of the SMN2 gene, they may be able to produce more SMN protein to make up for deficits related to their SMN1 gene mutations.

According to the Muscular Dystrophy Association, there are a number of potential genetic causes for distal SMA not related to the SMN1 gene. Identified genes attributed with distal SMA include:

  • UBA1
  • DYNC1H1
  • TRPV4
  • GARS
  • FBXO38

If you have reason to believe your future child may have SMA due to a family history with the disease, chorionic villus sampling or amniocentesis can be carried out during pregnancy to check for the condition.

After babies are born, a blood test is available that can be used to diagnose the condition. In some cases, physical examination and other muscular testing like an electromyography or muscle biopsy may be necessary.

There’s currently no cure for distal SMA, but a doctor can work with you to create an individualized treatment plan that offers relief from your symptoms.

As a part of these treatment plans, various medications have been approved by the Food and Drug Administration (FDA). These include:

  • Nusinersen (Spinraza): This drug is designed to increase the production of SMN protein in children and adults with SMA.
  • Onasemnogene abeparovec-xioi (Zolgensma): This is a gene therapy for children younger than 2 years of age diagnosed who’ve received a diagnosis of SMA.
  • Risdiplam (Evrysdi): This is an oral drug approved for those with SMA who are 2 months or older.

The cost of these medications can vary depending on where an individual purchases them and their insurance coverage.

In addition to medications, physical therapy and occupational therapy may be beneficial for those with distal SMA.

The use of mobility devices like wheelchairs and walking frames may be suggested by doctors depending on the extent of your muscle loss. Braces, splints, and even shoe inserts can also be useful.

It’s important that individuals with SMA get an appropriate amount of nutrients and sleep to maintain their strength. In some cases, feeding tubes and ventilation devices may be required to do this.

The life expectancy and outlook for those with SMA typically depends upon the type they have. Those with type 1 have a very low life expectancy, potentially even dying within the first months of life, while those with type 4 may not experience any impact on their life expectancy.

Medical advances have made it possible for some individuals with severe SMA to live longer than expected, so it’s possible that the outlook for those with SMA could improve in the future.

Distal SMA is a type of SMA that mainly affects an individual’s limbs. Caused by genetic mutations, symptoms can include trouble walking and weakness in your arms and legs.

Although there’s no cure, physical therapy, a nutritious diet, and assistive devices like walkers or braces can help. It’s important to talk with a doctor if you believe you’re experiencing symptoms of SMA at any age.