What is Spinal Muscular Atrophy Type 0?

Spinal muscular atrophy (SMA) type 0 is a rare genetic disorder that affects the ability to control muscle movement. It’s present before birth, and infants born with the condition will need immediate care.

SMA is a genetic condition that inhibits a person’s ability to control muscle movement, resulting in varying degrees of muscle weakness and wasting.

Spinal muscular atrophy type 0, also called prenatal SMA, is the rarest and most severe form of spinal muscular atrophy (SMA). It appears at birth, and healthcare professionals can also detect it on an ultrasound before an infant is born.

While there’s currently no cure for SMA type 0, medications, physiotherapy, and supportive care can improve a baby’s quality of life.

Read on to learn more about SMA type 0.

What is it?

SMA type 0 is an inherited neuromuscular disease caused by a mutation in the SMN1 gene. It causes a progressive loss of motor neurons, the nerve cells that control voluntary movement.

In general, SMA is an autosomal recessive disease. That means that symptoms will only develop if a disease-causing mutation on the SMN1 gene is inherited from each parent. If only one of the mutated SMN1 genes is inherited, no symptoms would develop, but that person would be a carrier of the gene.

SMA type 0 is the most severe form of SMA, and infants born with type 0 immediately have severe symptoms of muscle weakness and low muscle tone at birth. They often can’t respond to outside stimuli and have difficulty breathing, heart disease, and can’t feed on their own.

Symptoms

SMA type 0 is present before birth, and symptoms may be noticeable during pregnancy. Often, the first detectable symptom is reduced fetal movement and a lack of movement later in pregnancy.

Additional signs and symptoms in babies with SMA type 0 are:

• severe weakness
• hypotonia (loss of muscle tone)
• facial muscle paralysis
• contractures (joint deformity and tightening)
• congenital heart defects
• severe respiratory muscle weakness

Diagnosis

The only way to confirm a diagnosis of SMA type 0 is through genetic testing . Healthcare professionals do this using a blood sample to identify mutations in the SMN1 gene.

Since the genes that cause SMA type 0 are present from conception, doctors can test the fetus during pregnancy. If you have a family history of SMA, it may be a good idea to have genetic testing early in pregnancy.

Newborn screening can also detect SMA type 0 through a simple blood test. As of 2021 , 34 states in the Unites States had included SMA testing as part of their newborn screening protocols.

How rare is it?

SMA type 0 is very rare. However, experts aren’t sure just how rare it is — this is because SMA type 0 was first described in the 1990s, and experts have documented only a few dozen cases.

The full spectrum of SMA diseases only affects 1 in 10,000 live births, making it a very rare condition overall. Type 0 is the rarest form of the condition.

Treatment and supportive care

There’s currently no cure for any type of SMA, and treatment of SMA type 0 is usually focused on supportive care. The aim is to improve a baby’s quality of life.

Your pediatrician may recommend chest physiotherapy and antibiotics. Also, ventilators and feeding tubes can help with breathing and nutrition.

Three FDA-approved medications for SMA are available. Still, because type 0 is so rare, experts don’t know just how effective they are in managing this form of the condition.

Emerging research and clinical trials continue to explore effective treatments for SMA type 0 and other forms of SMA.

Available medications include:

• Nusinersen (Spinraza): This was the first drug FDA-approved for SMA.
• Risdiplam (Evrysdi): This is the first oral medication approved for the condition.
• Onsemnogene abeparvovc-xioli (Zolgensma): This medication is approved for children under age 2.

Life expectancy and outlook

An infant born with SMA type 0 doesn’t usually live longer than 6 months. While supportive care such as breathing treatments and physical therapy may improve quality of life, these infants have a reduced life expectancy.

Research into treatments and better supportive care for SMA type 0 is ongoing. New medications and emerging forms of gene therapy could eventually improve the outlook for infants with the condition.

Support for families

Experiencing an SMA type 0 diagnosis in your family can be overwhelming and challenging. While it’s important to reach out to loved ones, organizations and resources are also available for information and support:

• CureSMA
• Muscular Dystrophy Association
• SMA Foundation
• Pediatric Neuromuscular Clinical Research Network
• MySMATeam

The bottom line

SMA type 0 is an extremely rare and very serious form of spinal muscular atrophy. It’s present before birth and healthcare professionals may detect it during pregnancy.

Infants born with SMA type 0 have reduced muscle tone, possible heart defects, and a reduced life expectancy, often dying before 6 months of age.

While there’s currently no cure for SMA type 0, emerging research could help slow the progression of the disease.