What is Spinal muscular atrophy (SMA)?
SMA is a hereditary motor neuron disease that causes muscle weakness and atrophy.
SMA is characterized by progressive degeneration and muscle weakness and atrophy resulting from the irreversible loss of anterior horn cells in the spinal cord and brainstem nuclei. Motor neurons control movement in the arms, legs, chest, face, throat, and tongue. When signals between motor neurons and muscles are interrupted, the muscles gradually weaken, begin to exhaustion, and fasciculations occur.
SMA can affect a child’s ability to crawl, walk, sit, and control head movements. Severe SMA can damage the muscles used for breathing and swallowing.
The age of onset of clinical signs of the disease may vary from birth to adulthood. Muscle weakness is symmetrical and progressive.
What are the symptoms of SMA disease?
The symptoms and age of onset can vary depending on the type of SMA. Typical symptoms are:
SMA does not affect intelligence or cause learning difficulties.
What are the SMA types?
The most common type is “SMA disease associated with SMN”. SMN-associated SMAs are divided into 4 types according to the age of onset and the severity of clinical findings. In addition, the SMN2 copy number is among the determining factors of the SMA type.
In addition, it is known that many gene mutations other than SMN1, although rare, cause SMA-like clinic.
How is SMA Diagnosed?
The most common type of SMA, “SMN-associated SMA disease”, is determined by the identification of biallelic pathogenic variants in SMN1. SMN2 copy number is generally among the factors affecting the phenotype.
Treatment in SMA
SMA is inherited in an autosomal recessive pattern. In the case of consanguinity, the couples are at increased risk of becoming asymptomatic carriers of the same disease. In cases where the mother and father are asymptomatic carriers of SMA, there is a 25% risk of having children diagnosed with SMA in each pregnancy. These couples should be informed about Preimplantation Genetic Diagnosis (PGD) and prenatal diagnosis methods.