Spinal muscular atrophy (SMA)
- Dec 20, 2022
- 3 min read
Is a group of hereditary diseases that progressively destroys motor neurons—nerve cells in the brain stem and spinal cord that control essential skeletal muscle activity such as speaking, walking, breathing, and swallowing, leading to muscle weakness and atrophy.
What causes SMA?
The most common form of SMA is caused by defects in both copies of the survival motor neuron 1 gene (SMN1) on chromosome 5q. This gene produces the survival motor neuron (SMN) protein which maintains the health and normal function of motor neurons. Individuals with SMA have insufficient levels of the SMN protein, which leads to loss of motor neurons in the spinal cord, producing weakness and wasting of the skeletal muscles. This weakness is often more severe in the trunk and upper leg and arm muscles than in muscles of the hands and feet.
How is it inherited?
Except in the rare cases caused by mutations in the UBA1 gene, SMA is inherited in an autosomal recessive manner, meaning that the affected individual has two mutated genes, often inheriting one from each parent.
Those who have only one mutated gene are carriers of the disease without having any symptoms.
Autosomal recessive diseases may affect more than one person in the same generation (siblings or cousins).
What are the types of SMA?
Type I, also called Werdnig-Hoffmann disease or infantile-onset SMA, is evident usually before 6 months of age. Without any treatment, affected children never sit or stand and the vast majority usually die of respiratory failure before the age of 2 years.
SMA type II, the intermediate form, usually show their first symptoms between 6 and 18 months of age although some can present earlier. They are able to sit without support but are unable to stand or walk unaided,. Life expectancy is reduced but most individuals live into adolescence or young adulthood.
SMA type III (Kugelberg-Welander disease) develop symptoms after 18 months of age and can walk independently. Individuals with SMA type III may be prone to respiratory infections, but with care most have a normal lifespan
Individuals with SMA type IV develop symptoms after 21 years of age, with mild to moderate proximal muscle weakness and other symptoms. It is the mildest form and those affected live relatively normal life with more frequent treatable respiratory infections
How is SMA diagnosed?
A blood test is available to look for deletions or mutations of the SMN1 gene. This test identifies at least 95 percent of SMA Types I, II, and III and may also reveal if a person is a carrier of a defective gene that could be passed on to children.
Are there treatments for SMA?
There is no cure for SMA. Treatment consists of managing the symptoms and preventing complications.
In December 2016 the U.S. Food and Drug Administration approved nusinersen (Spinraza™) as the first drug approved to treat children and adults with SMA. The drug is administered by injection into the fluid surrounding the spinal cord.
There are many research underway using Stem Cells.
What is the prognosis?
Prognosis varies depending on the type of SMA. Some forms of SMA are fatal without treatment.
Milder forms of SMA may appear to be stable for long periods, but improvement should not be expected without treatment.
Where can I get more information?
Stay tuned to drtaraben.com for the latest on Stem Cell & Gene Therapies.
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