Spinal Muscular Atrophy is a genetic disorder that affects motor neurons. The protein needed to keep these motor neurons alive is not coded correctly by the SMN1 gene. Motor neurons cannot survive with protein support and thus die. As motor neurons die, the patient loses the ability to use certain muscles. There are multiple forms of the disease, including:
- Type I – Werdnig-Hoffmann disease
- Type II – Dubowitz disease
- Type III – Kugelberg-Welander disease
- Type IV – Adult-onset
Who is at Risk?
Spinal Muscular Atrophy is an inherited condition. About 1 in 6-10,000 people or about 50,000 people in the United States suffer from spinal muscular atrophy. SMA is considered a "rare disease" affecting less than 200,000 people in the US. The gene frequency is about 1 in 100 people, which means that about 1 in 50 people are carriers of the recessive gene.
Children of two parents carrying the affected gene can be affected by the disorder. Typically, children have a 25-percent chance of developing no affected genes, 25-percent chance of developing the condition and a 50-percent chance of being a carrier of the disease.
There is also an X-chromosome variety of Spinal Muscular Atrophy, which mainly affects male children. The X-chromosome variety is passed on to male children with the X chromosome from the affected mother. In order for the condition to be passed on to a female child, both X chromosomes must be affected, which is highly unlikely.
Symptoms of Spinal Muscular Atrophy vary with type and age when symptoms present. The severe variety the disorder is recognizable soon after birth, often at birth. Newborn often require intensive care treatment, including respiratory support and often succumb to respiratory failure within a few weeks. In rare cases, children with the most severe form of the disorder may live up to two years.
Type II Spinal Muscular Atrophy typically presents with weakened muscles between six and 18 months of age. The progression of the disease varies among patients, but with medical care, many patients live into adulthood.
If a child reaches 18 months of age before symptoms begin, the prognosis is good. Symptoms will include reduced muscle strength and eventually, patients will lose the ability to walk.
Adult-onset Spinal Muscular Atrophy is the mildest form of the disease. Patients show signs of the disease after the age of 35 with a progressive loss of muscle function. Most patients eventually need to use a wheelchair.
The most severe form of Spinal Muscular Atrophy is recognizable at birth. Babies are often characterized as “floppy” due to lack of muscle development and strength. Others forms of the disease are diagnosed with a combination of medical history, symptom reporting, and genetic testing.
Treatment for Spinal Muscular Atrophy is symptomatic. Patients typically require physical therapy, respiratory care, and mobility assistance. Respiratory function is the primary concern for most patients with moderate to severe forms of the disease as death can occur if respiratory muscles are affected.
Patients presenting with severe symptoms at birth have a significantly reduced life span. Most infants with Type I Spinal Muscular Atrophy will succumb to the disease before the age of two. As the infant reach developmental milestones, the risk of early death decreases.