SMA- Spinal Muscular Atrophy (SMA) refers to a group of inherited diseases of the motor nerves that cause muscle weakness and atrophy. The motor nerves arise from the spinal cord and control the muscles that are used for activities such as breathing, crawling, walking, head and neck control, and swallowing. SMA is a rare disorder occurring in approximately 8 out of every 100,000 live births, and affecting approximately 1 out of every 6,000 to 10,000 individuals worldwide.
SMA is caused by a missing or abnormal (mutated) gene known as survival motor neuron gene 1 (SMN1). In a healthy person, this gene produces a protein in the body called survival motor neuron (SMN) protein. In a person with mutated genes, this protein is absent or significantly decreased, and causes severe problems for motor neurons. Motor neurons are nerve cells in the spinal cord which send out nerve fibers to muscles throughout the body. Since SMN protein is critical to the survival and health of motor neurons, nerve cells may shrink and eventually die without this protein, resulting in muscle weakness. As a child with SMA grows, it is difficult for his/her weakened muscles to keep up with the demands of daily activities. The resulting weakness can also lead to bone and spine changes that may cause breathing problems and further loss of function.
SMA affects muscles throughout the body. In the most common types, weakness in the legs is generally greater than in the arms. Sometimes feeding, swallowing, and respiratory function (e.g., breathing, coughing, and clearing secretions) can be affected. When the muscles used for breathing and coughing are affected and weakened, this can lead to an increased risk for pneumonia and other respiratory infections, as well as breathing difficulty during sleep. The brain’s cognitive functions and the ability to feel objects and pain are not affected.
There are four types of SMA: Type I, II, III, and IV. The determination of the type of SMA is based upon the physical milestones achieved. It is important to note that the course of the disease may be different for each affected individual. Although SMA is not generally regarded as a progressive disease, people affected with SMA typically lose function over time as muscles continue to weaken. Loss of function may occur gradually or more rapidly in the context of a growth spurt or illness. The reasons why muscle weakness and subsequent loss of function occur at different rates in different individuals remain poorly understood. It has been observed that individuals with SMA may be very stable in terms of their abilities for prolonged periods of time, often years, although the almost universal tendency is for continued loss of body function as they grow older.
Today, new advances in research are giving new hope to people affected by the disease.