Spinal Muscular Atrophy (SMA): Symptoms and Diagnosis
As a follow up to my previous article “Spinal Muscular Atrophy (SMA): Introduction“, I am posting here the symptoms of the disease as well as its diagnosis.
Infantile SMA is the most severe form. Some of the symptoms include:
- muscle weakness
- poor muscle tone
- weak cry
- limpness or a tendency to flop
- difficulty sucking or swallowing
- accumulation of secretions in the lungs or throat
- legs that tend to be weaker than the arms
- hypotonia, areflexia, and multiple congenital contractures (arthrogryposis) associated with loss of anterior horn cells
- feeding difficulties
- increased susceptibility to respiratory tract infections
- developmental milestones, such as lifting the head or sitting up, can’t be reached.
In general, the earlier the symptoms appear, the shorter the life span. The onset is sudden and dramatic. Once symptoms appear the motor neuron cells quickly deteriorate shortly after. The disease can be fatal and there is no cure for SMA yet known. The major management issue in Type 1 SMA is the prevention and early treatment of respiratory infections; pneumonia is the cause of death in the majority of the cases. The average life expectancy is 1 year for Type 1 SMA, 20 years for Type 2 (sometimes longer), and Type 3 can have a regular life span. Intellectual and sexual functions are generally unaffected by SMA.
Diagnosis of SMA
In order to be diagnosed with Spinal Muscular Atrophy, symptoms need to be present. In most cases a diagnosis can be made by the SMN gene test, which determines whether there is at least one copy of the SMN1 gene by looking for its unique sequences (that distinguish it from the almost identical SMN2) in exons 7 and 8. In some cases, when the SMN gene test is not possible or does not show any abnormality, other tests such as an EMG electromyography (EMG) or muscle biopsy may be indicated.
