Spinal muscular atrophy, or SMA, is the name given to a group of inherited disorders characterized by symptoms of progressive muscle weakness and wasting. SMA affects nerve cells (also called motor neurons) that control voluntary muscles, causing them to die off. Due to the loss of motor neurons, the spinal cord is unable to send messages to the muscles, preventing their normal function and leading to their atrophy (wasting away).
SMA affects voluntary muscles, including those that control the legs, arms and face, as well as movements such as breathing or swallowing. SMA does not affect sensations such as touch, heat and pain. It also has no effect on intelligence.
How SMA is Transmitted
SMA is transmitted through autosomal recessive inheritance. In other words, the gene that causes SMA can remain ‘hidden’ for generations before two people who both have the recessive gene become partners and have children. For this reason, parents can unknowingly pass SMA and other neuromuscular disorders on to their infants.
According to awareness and advocacy organization Families of Spinal Muscular Atrophy, there are four types of SMA. The most severe type usually affects children by the time they are six months of age and is also the most deadly.
Frequency of SMA
According to the European Neuro Muscular Centre (EMNC), an international support organization for researchers in neuromuscular disorders, one in every 40 people are carriers of inherited gene abnormalities that cause SMA. Forms of the disease can strike any age, race or gender. According to the EMNC, a child has a one in four chance of developing SMA if both parents are carriers.
Families of SMA reports that spinal muscular atrophy is the leading genetic killer of children under the age of two. The organization estimates that 7.5 million Americans carry the gene that causes SMA and one in every 6,000 babies is born with the disorder.
In children, first signs of muscular degeneration can include difficulty running, climbing stairs, or getting up off the floor. Symptoms become progressively worse as the affected child grows older. Type IV SMA appears in adults, usually in their mid-30s. A form of SMA called Spinal Bulbar Muscular Atrophy, or SBMA, affects about one in 40,000 adults worldwide. It is also known as Kennedy's Syndrome.
Resources For Persons Diagnosed With SMA
Families of SMA and the Muscular Dystrophy Association in the United States both offer in-depth information on neuromuscular disorders. Support is available for patients diagnosed with neuromuscular disorders and their families worldwide, including in Canada, the U.S., Australia and the United Kingdom.
SMA is a relatively rare group of neuromuscular disorders. Forms of childhood muscular dystrophy can also produce muscle weakness. Parents concerned about the onset of signs of muscle weakness or coordination problems in their children should seek medical advice from a specialist. If symptoms cannot be diagnosed, the family may be asked to undergo testing to rule out an underlying genetic cause.
Anne Williams - Anne is a freelance writer and communications consultant based in Vancouver, Canada.
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