Spinal muscular atrophy, or SMA, is generally observed in infants and young children. An inherited health disorder, SMA affects the muscles and nerves. Since the disease is degenerative, it causes progressive muscle decline, leading to mild or severe disability. While it is not preventable, it helps to learn all about it to seek timely diagnosis and treatment. To get started, here are some common causes, symptoms, and treatment options for spinal muscular atrophy. Causes of SMA The most common forms of SMA, that is, types 0 to 4, are caused by missing or mutated genes. Under usual circumstances, a gene known as SMN1 releases the SMN protein, which helps the motor neurons to thrive and function properly. But in some cases, the SMN1 gene is mutated or is missing. This usually happens when a child has two copies of the malfunctioning gene, each inherited from one parent. Therefore, those who have SMA are not able to make enough SMN protein. Subsequently, the motor neurons are unable to grow, and instead, they start to shrink and die out. The overall effect of this is the brain is unable to control most of the voluntary movements, typically involving movement in the neck, arms, head, and legs.