SMARD is a rare genetic condition that affects your motor neurons. Symptoms such as breathing difficulties appear during infancy and can shorten life expectancy. There’s no cure, but emerging treatments are promising.

Spinal muscular atrophy with respiratory distress (SMARD) is a rare and severe genetic disorder that typically appears in early infancy.

SMARD damages the motor neurons, which control movement and muscle tone. It causes life threatening breathing difficulties. Most infants with SMARD require a ventilator.

Read on for an overview of SMARD causes, symptoms, diagnosis, and more.

SMARD is due to an inherited genetic mutation that destroys motor neurons. Motor neurons control communication between the spinal cord and muscles. When they stop working, muscles become weak and waste away.

SMARD is an autosomal recessive condition, meaning both parents must carry the genetic mutation and pass it on for their child to develop SMARD.

It’s possible to carry the genetic mutation for SMARD without having the condition yourself. If your partner also has the mutation, you have a 25% chance of having a child with SMARD and a 50% chance of having a child who carries the genetic mutation for SMARD.

SMARD1 vs. SMARD2

Researchers have identified two types of SMARD.

SMARD type 1 results from mutations in a gene called immunoglobulin mu-binding protein 2 (IGHMBP2). This gene helps make the IGHMBP2 protein. In SMARD1, mutations lead to an abnormal IGHMBP2 protein that harms motor neurons in the spinal cord.

Very little is known about SMARD type 2. It causes symptoms similar to SMARD1, but a different genetic mutation appears to be the cause.

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SMARD is a rare variant of spinal muscular atrophy (SMA) that typically appears in babies ages 1–6 months old. It can, however, appear slightly earlier or later.

Experts think SMARD1 and SMARD2 are both very rare. But there’s no prevalence data available to show just how rare they are.

Some estimates suggest they affect less than 1 in 100,000 people each. But since SMARD is a genetic condition, it might be more common in certain populations.

SMARD doesn’t always have a predictable course, and symptoms can vary a lot from one child to the next.

Signs and symptoms of SMARD during pregnancy can include:

Symptoms of SMARD in newborns can include:

  • loud or labored breathing
  • difficulty suckling
  • difficulty gaining weight (failure to thrive)
  • a weak cry
  • weak or floppy arms and legs
  • recurrent respiratory infections
  • misformed feet

Doctors often diagnose SMARD after an infant is admitted to the hospital for acute respiratory failure. Since the condition is very rare, it can take several months to get a diagnosis.

Usually, a doctor who specializes in pediatric neuromuscular disorders will analyze your child’s symptoms and conduct a physical examination. If they suspect SMARD or another condition, they might also conduct:

There are few available treatments for SMARD. Most children with SMARD require a ventilator to breathe and ongoing physical therapy to retain muscle function.

Some promising treatments are currently in development. In particular, gene therapy for SMARD1 is undergoing clinical testing. This treatment involves an injection that contains a corrected IGHMBP2 gene to replace the mutation.

The outlook for babies with SMARD is often poor. Although the average life expectancy is unknown, many children pass away in their first or second year of life due to breathing difficulties or complications from respiratory infections.

According to the authors of a 2019 review, the outlook also likely depends on factors such as how early SMARD appears, with a later onset linked to a milder form of the condition. In addition, quick treatment may help to preserve muscle function.

The oldest known person living with SMARD was 21 years old in 2019, according to the authors of the review.

Both SMA and SMARD are inherited autosomal recessive conditions that affect the motor neurons in the spinal cord. They can both cause difficulties with breathing, swallowing, sitting up, and movement in general.

With SMARD, though, severe breathing difficulties are typically among the first symptoms. Babies with this condition usually develop weakness in their arms and legs after developing respiratory problems.

With SMA, the opposite is true. Babies with SMA usually have weak limbs and later show breathing difficulties.

Finally, types 1—4 of SMA are all linked to problems with survival motor neuron (SMN) genes 1 and 2, in contrast with SMARD1, which is linked to IGHMBP2.

Does spinal muscular atrophy affect the respiratory system?

Most types of SMA eventually affect the muscles that control breathing. As the condition progresses, it may cause respiratory problems.

What is the common cause of death in spinal muscular atrophy?

Respiratory infections such as pneumonia are a common cause of death in both SMA and SMARD. Both illnesses make it difficult to breathe and cough.

Can SMA cause shortness of breath?

Babies and children with SMA can experience shortness of breath and other respiratory difficulties. However, this symptom often appears later on when the illness has progressed.

SMARD is a rare genetic disorder that affects newborns. Research has linked it to mutations in the IGHMBP2 gene that are passed on from parent to child. Having two copies of the mutated gene (one from each parent) results in the condition.

SMARD has a lot in common with SMA. But with SMARD, severe breathing problems are among the first symptoms to appear. Babies with SMARD might also experience frequent respiratory infections or have difficulty crying loudly.

Gene therapy is an up-and-coming treatment for SMARD type 1 that is currently in the clinical trial phase. Learn more about these clinical trials.