SMA: The Facts:
- SMA is an autosomal recessive genetic disease characterized by the dramatic loss of spinal motor neurons, resulting in muscle weakness, atrophy, and in the worst cases, the loss of ability to swallow and breathe all leading to paralysis and then death. SMA affects the voluntary muscles for activities such as crawling, walking, head and neck control as well. The mind remains unaffected, while the muscles waste away. Children with SMA are very bright, playful and very social.
- SMA is incurable, untreatable, fatal, and underfunded.
- 1 in 40 people are genetic carriers of SMA. That means 7 million potential parents, most unknowingly, carry the abnormal gene.
- Approximately 1 in 6000 babies are born with SMA; two children each day in the United States. Over 60% of children are diagnosed before 6 months of age and 90% of those children will die before their second birthday.
- SMA is relatively common yet virtually unheard of in the general public. SMA is as common as Cystic Fibrosis in the entire population and Tay-Sachs in the Jewish population.
- Many families who have children with SMA have NO FAMILY HISTORY of the disease.
- SMA can strike anyone of any race or gender
- Respiratory illnesses are of a great concern to patients with SMA as the muscles used to breath and swallow are affected. Many babies with SMA die from respiratory illnesses.
- SMA presents in a broad clinical spectrum and is classified into four types based on disease severity: SMA Type I, II, III, and IV. Click here for more information of the types of SMA. The determination of the type of SMA is based upon the physical milestones achieved. Approximately 65% of all new SMA patients are type I severe or type II.
- SMA children with the most severe form (Type I) often face quickly increasing muscle weakness, leading to paralysis and death.
- SMA kills more babies than any other genetic disease. It is the #1 genetic killer of children under the age of 2
What Causes SMA?
SMA is an autosomal recessive neurodegenerative disease. In order for a child to be affected by SMA, both parents must be carriers of the abnormal gene and both must pass this abnormal gene on to their child. If both parents are carriers the likelihood of a child inheriting the disorder is 25%, or 1 in 4. If both parents are carriers of SMA the likelihood of a child who is a carrier of SMA is 50%, or 2 in 4. If both parents are carriers of SMA the likelihood of a child with who is neither a carrier of SMA nor affected with SMA is 25%, or 1 in 4.
SMA occurs when a vital gene (“survivor motor neuron” gene or “SMN”) is deleted or mutated, preventing the creation of a protein necessary for muscle strength. A second, nearly identical copy gene, SMN2, is present in all SMA patients. SMA disease severity correlates inversely with increased SMN2 gene copy number.
SMA Carrier Testing- Preventing SMA
There is currently a simple blood test that can be done to determine if you are a carrier, yet few know to ask for it. The American College of Medical Genetics recommends that SMA carrier testing be made available to ALL couples planning a family, regardless of ethnicity or family history.
If you and your partner are found to be carriers of SMA there are many options. Many couples decide to have prenatal testing, such as amniocentesis or CVS; Accept this level of risk and have children without further testing; Go through in vitro fertilization and test the embryos using Preimplantation Genetic Diagnosis (PGD); Adopt; Use donor sperm or donor eggs; Not have other children. A genetic counselor can explain each of these. No matter what decision is made, it is the best decision for you and your family whatever you may chose.
Carrier Testing Information: