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Spinal Muscular Atrophy
What is Spinal Muscular Atrophy?
Spinal muscular atrophy (SMA) is a genetic health condition affecting the nerves within the spinal cord. This condition affects muscle movement and control of the body, including; arm and leg movement, breathing, and coughing. SMA is a genetic condition inherited from parents where both parents have the affected SMN1 recessive gene. SMA impacts 1 in every 10,000 people.
SMA Subtypes and Symptoms
SMA can be classed into 5 types based on the severity and the onset of symptoms.
Type 0: Type 0 is the most severe form of SMA, presenting before birth. Typical features include less movement in the womb, birth with joint deformities, weak muscle tone at birth, and respiratory and heart defects. Without treatment intervention the life expectancy is usually less than 12 months.
Type 1: Type 1 also known as werdnig-hoffman disease, presents symptoms within the first few months of life (0-6 months). Typical features of type 1 include; profound weakness and hypotonia, weak cry and cough, difficulty swallowing, respiratory insufficiency, and aspiration pneumonia. Without interventions, type 1 children may never sit. Type 1 SMA affected children have a life expectancy usually less than 2 years old.
Type 2: Type 2 is an intermediate presentation, typically identified by a delay in motor milestones, poor weight gain, weak cough, fine hand tremors, joint contractures and scoliosis. Often onset is visible within the age of 7-18 months. SMA type 2 if untreated will never stand, and have a predicted life expectancy of greater than 2 years.
Type 3: Type 3 also known as Kugel-Welander, is a mild presentation of SMA. Left untreated individuals with SMA type 3 will have the ability to stand and walk, however features of variable muscle weakness and cramp, joint overuse, and loss of walking ability, will typically present. Type 3 individuals are usually diagnosed after 18 months of age and have a life expectancy of adulthood.
Type 4: Type 4 is adult onset SMA, this type is rare and presents at early adulthood. The symptoms are mild and typically present through mild to moderate muscle weakness, tremors, and mild breathing problems.
Treatment and Support
There is currently no cure for SMA, however, treatments for SMA are being explored, these future treatments target the back-up gene (SMN2), aiming to replace and increase working copies of the SMN2 gene. Those living with SMA can be supported through treatments and services which may include; breathing support, feeding support (such as feeding tubes), mobility equipment, physiotherapy, and treatment for scoliosis. Living with SMA does not impact intelligence. Where possible, children and adults with SMA are encouraged and supported to participate in activities, education and work, to live a full life.
Diagnosis of Spinal Muscular Atrophy
Diagnosing SMA usually begins with concerns raised in a routine physical exam, and is confirmed by molecular genetic blood testing. Prospective parents can undertake carrier screening to determine if they carry the condition this can be conducted by cheek swab testing.
