Spinal muscular atrophy (SMA) is a motor neuron (motor cell) disorder group. These disorders are transmitted from parents to children (hereditary) and can appear at any stage of life. The disorder leads to muscle weakness and atrophy.
Causes: SMA is a group of diseases of the motor nerves (or neurons). The disease is caused by a lack of protein (SMN) due to defective genes.
Most of the time, a person has to inherit one copy of the defective gene from both parents to be affected. The most severe form is SMA type I, also called Werdnig-Hoffman disease. Babies with SMA type II have less severe symptoms early in the breastfeeding period, but they weaken over time. SMA type III is a less severe form of the disease.
In rare cases, SMA begins in adulthood. This is the mildest form of the disease.
A family history of SMA in an immediate family member (such as a brother or sister) is a risk factor for all types of this disorder.