Distal spinal muscular atrophy (DSMA) is a rare genetic disease that causes a loss of muscle movement. It affects muscles further away from the center of the body, such as the hands, feet, and legs.

DSMA is a type of spinal muscular atrophy (SMA). This term describes conditions that cause muscle weakness and atrophy, which refers to muscles wasting away or shrinking.

There are several types of SMA, and DSMA describes a type that affects muscles further away from the center of the body. People may also refer to DSMA as distal spinal muscular atrophy type 5.

Presently, there is no cure for SMA, but a doctor can help treat the symptoms. Usually, treatment plans are highly individual and depend on the type of SMA someone has.

Read on to learn more about DSMA and its treatment.

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DSMA is a term that describes a muscle-wasting disease that can affect muscles furthest away from the center of the body.

These include the muscles of the lower arms, legs, and feet. A rare type of DSMA, known as spinal muscular atrophy with respiratory distress (SMARD), can cause breathing problems and muscle weakness.

Health experts may also refer to DSMA as distal hereditary motor neuropathy.

DSMA is a type of SMA, which can also affect muscles close to the center of the body.

The charity Spinal Muscular Atrophy UK states that genetic alterations in the BSCL2, GARS1, and REEP1 genes can result in DSMA.

BSCL2 is a gene that provides instruction for a protein known as seipin. Currently, researchers are unsure of the exact function of seipin. However, variations in the BSCL2 gene likely alter the structure of seipin and cause it to accumulate and damage motor neurons. Motor neurons are cells in the brain and spinal cord that allow for movement, speech, and other important bodily functions.

The GARS1 gene helps produce an enzyme known as glycine-tRNA ligase. At present, it is unclear how alterations in this gene cause DSMA. However, it may be due to changes in this enzyme reducing its activity, which impairs the ability of nerve cells to communicate with muscles in the hands and feet.

REEP1 is responsible for producing the protein known as receptor expression-enhancing protein 1. This protein is present in nerve cells in the brain and spinal cord. While health experts do not know its exact function, changes to its shape likely affect its ability to function correctly.

However, variations in other genes may also cause DSMA. These may include:

  • UBA1
  • DYNC1H1
  • TRPV4

Alterations in the SMN1 gene cause other SMA conditions. The SMN1 gene makes proteins essential to motor neuron survival. When someone has a deficiency in the SMN protein, their motor neurons will degrade and deteriorate with time.

There is another gene that can make some motor neuron proteins, known as SMN2. However, it cannot compensate for the loss of protein from a variation in the SMN1 gene. That said, a person’s symptoms may develop later in life and could be milder if they have more copies of the SMN2 gene.

The symptoms of DSMA vary depending on the stage of the disease. People may first notice cramps in their hands that can trigger due to cold weather. This may start in adolescence, though in some people, it may be as late as their mid-30s.

As symptoms progress, a person may also experience:

  • weakness in hands
  • wasting, or atrophy, in hand muscles
  • problems with walking as the muscles in the legs begin to deteriorate

SMARD is a rare form of SMA that affects infants and can cause respiratory distress.

However, other types of SMA can affect other areas of the body.

Type 1 SMA

Type 1 SMA predominantly affects infants in their first 6 months of life.

Babies with type 1 SMA typically show the following signs and symptoms:

  • weak and floppy arms and legs
  • problems with eating, swallowing, and breathing
  • not being able to sit unsupported or raise their head

Type 2 SMA

Type 2 SMA affects children slightly later in life from 7 to 18 months old. These symptoms are usually less severe than those observable in type 1.

Children with type 2 SMA may have the following symptoms:

  • sitting up without assistance but being unable to walk or stand
  • weakness in the arms and legs
  • shaking or tremors in hands and feet
  • problems with joints
  • curved spine, known as scoliosis
  • trouble breathing
  • chest infections

Type 3 SMA

Type 3 SMA can appear in late childhood and early adulthood. However, symptoms may appear as early as 18 months.

People with type 3 SMA may experience:

  • difficulty getting up and standing
  • issues with balance
  • difficulty running
  • difficulty climbing stairs
  • slight shaking or tremors in their fingers

Over time, a person may find walking becomes increasingly difficult and that they can no longer walk as they get older.

Type 4 SMA

Symptoms of type 4 SMA usually begin in early adulthood. This type is also degenerative, as symptoms gradually worsen with time. However, a person does not lose their ability to breathe or swallow.

Generally, symptoms include:

  • weakness in the hands and feet
  • problems with walking
  • tremors or twitching muscles

When a doctor suspects a person has an SMA, they will request a blood test to screen for variations and deletions of certain genes. For DSMA, a healthcare professional will screen for genes such as BSCL2, GARS1, and IGHMBP2. If they cannot identify a gene variation, or a person’s medical history suggests their risk for DSMA is low, a doctor may also request the following tests:

  • Electromyography: This test records the electrical activity of muscles when in a state of contraction and at rest.
  • Nerve conduction velocity study: This study measures the nerve’s ability to transmit an electrical signal.
  • Muscle biopsy: This involves a doctor analyzing a sample of the muscle to screen for other health conditions.

There is currently no cure for DSMA, so doctors help people manage their symptoms instead.

Generally, physical therapy and occupational therapy can help prevent further muscle weakness and help maintain joint mobility for longer. Exercises that include stretching and strengthening can also help preserve a person’s range of motion.

As the disease progresses, people must maintain adequate levels of nutrition. If they cannot swallow, they may need a feeding tube. Additionally, they may require mobility devices when they lose their ability to walk and get up.

For other types of SMA, the Food and Drug Administration (FDA) has given approval to medications to help treat the condition.

Read on to learn more about SMA treatment.

DSMA affects muscles that are further away from the center of the body. However, other types of SMA can affect muscles closer to the center of the body and reduce a person’s ability to breathe and swallow.

While there is currently no cure for DSMA, a doctor can treat a person’s symptoms with physical therapy and ensure they follow a nutritious diet. As the disease progresses, they may need help from either mobility aids or other medical devices.