Spinal muscular atrophy (SMA) is a genetic disease affecting the part of the nervous system that controls voluntary muscle movement. SMA involves the loss of nerve cells called motor neurons in the spinal cord and is classified as a motor neuron disease.
In Pakistan there is no study available to measure its frequency, however in the United States, 1 in every 6,000 to 10,000 people develop spinal muscular atrophy and 1 in 50 is a carrier of the disease. It has been found in people of every race, but is most common in Caucasians, of whom 1 in 35 is a carrier.
Genetic causes of SMA
The most common form of SMA (types 1-4) is caused by a defect (mutation) in the SMN1 gene on chromosome 5. (People have two SMN1 genes — one on each chromosome 5.) A mutation in the SMN1 gene leads to a deficiency of a motor neuron protein called SMN, for survival of motor neuron.
Life expectancy with spinal muscular atrophy
The lifespan of a Type 2 child varies. They could pass away at an early age or they could live well into adulthood. As with all forms of SMA, weakness increases over time. Type 3 children are diagnosed between 18 months of age and in early adolescence.
Molecular diagnosis of spinal muscular atrophy
To make a diagnosis of SMA, symptoms need to be present. When symptoms are present, diagnosis can be made by genetic testing. Gene alterations (mutations) in the SMN1 and VAPB genes cause SMA. Genetic testing for a mutation in the VAPB gene is done to diagnose the Finkel type SMA.