Spinal Muscular Atrophy (SMA) is the number one inherited cause of death in children under the age of two. SMA is a degenerative disease of the anterior horn cells. Anterior horn cells are located in the spinal cord. SMA affects the voluntary muscles for activities such as crawling, walking, head and neck control, and swallowing. It is a form of muscular dystrophy.
SMA mainly affects the proximal muscles or, in other words, the muscles closest to the point of origin – in this case, those closest to the trunk of one’s body. Weakness in the legs is generally greater than weakness in the arms. Some abnormal movements of the tongue, called tongue fasciculations, may be present. The senses/feelings are normal as is intellectual activity. In fact, it often is observed that children with SMA are unusually bright and sociable.
One in every 6,000 babies is born with SMA. SMA can strike anyone of any race or gender. One in every 40 people carries the gene that causes SMA – that’s approximately 8 million people in America alone.
Carrier testing for SMA can be done through a simple blood or saliva test, but you will need to ask your doctor for it. More information on genetic testing can be found at the following links:
- Counsyl (saliva test)
- Athena Diagnostics (blood test)
- UMass Lab Updates Newsletter (a very scientific explanation of SMA carrier testing results is on pages 3 and 4)
What Causes SMA?
Spinal Muscular Atrophy (SMA) is an autosomal recessive disease, which means that both parents must be carriers. Both parents must have the gene responsible for the disease, and these genes must be passed onto their child. When a child has received this gene from each of his or her parents, the child will then be affected by SMA. Although both parents are carriers the likelihood of passing this gene along to a child and having an affected child is 25 percent, or one in four.
Types of SMA
Type 0 is the most severe form of Spinal Muscular Atrophy and begins before birth. Usually, the first symptom of Type 0 SMA is reduced movement of the fetus, first seen between 30 and 36 weeks of the pregnancy. After birth, these newborns have little movement and have difficulties with swallowing and breathing.
Type I Acute (Severe) Werdnig-Hoffmann Disease
Type I is the most commonly diagnosed form of Spinal Muscular Atrophy with an incidence rate of 60 percent. This severe form of SMA is represented by the quick and unexpected onset of “floppy baby syndrome.” Diagnosis of Type I is usually made before six months of age, and, in the majority of cases, before three months. Children with Type I are not able to hold up their heads, roll over, crawl, sit up without support, or walk. They have difficulty with breathing, swallowing, feeding, and handling secretions. The life expectancy of children with SMA Type I historically was considered to be less than two years. However, with the recent introduction of proactive treatments, a longer survival and an improved survival rate have been reported.
Type II (Chronic)
Type II is the second most common form of Spinal Muscular Atrophy with an incidence rate of 27 percent. Diagnosis is almost always made between 15 months and two years of age. Children with Type II may sit unsupported, although they may need assistance. They may be able to learn to crawl or stand – often with the aid of braces and therapy. They typically will not be able to walk. In SMA Type II, life expectancy is somewhat reduced compared to the healthy population, although patients usually live to become parents and grandparents.
Type III (Mild) Kugelberg-Welander/Juvenile Spinal
Type III SMA is a milder form of Spinal Muscular Atrophy than types 0, 1, or 2. Symptoms appear between early childhood (older than age 1 year) and early adulthood. In the beginning, these children are able to stand and walk, but usually have difficulty doing so and may lose their ability over time. They typically have a normal lifespan, but eventually may be wheelchair bound.
Type IV (Adult-Onset)
Symptoms typically begin after age 35. This form of SMA is very rare. People with type 4 can walk, and that ability typically is not lost. Symptoms of adult-onset SMA are usually mild to moderate and include muscle weakness, tremors, and twitching. Proper diagnosis, genetic counseling and appropriate physical therapy remain common mainstays for treatment.
SMA with Respiratory Distress (SMARD)
SMARD is a neuromuscular condition causing weakness of the muscles. It is the second anterior horn cell disease in infants in which the genetic defect has been defined. SMARD is caused by mutations on the IGHMBP2 gene, whereas ‘regular’ SMA is caused by mutations of the SMN gene. Symptoms of SMARD are commonly seen within the first six months of life. The muscles used in breathing are severely affected in SMARD, causing paralysis of the diaphragm. Most children living with SMARD are trached and ventilated–without the diaphragm these children cannot breathe. Thanks to research taking place at The Jackson Laboratory, there is hope for the future for those affected by this disorder.
Adult Onset X-linked SMA (Spinal Bulbar Muscular Atrophy (SBMA) or Kennedy’s Syndrome)
This form of the disease occurs only in males, although 50 percent of female offspring are carriers. Adult Onset X-linked SMA is associated with a mutation in the gene that codes for part of the androgen receptor, and therefore these male patients often have breast enlargement known as gynoecomastia. Also noticeably affected are the facial and tongue muscles. The course of the disease is variable, but in general tends to be slowly progressive or nonprogressive.
VRK1 is a very rare form of Spinal Muscular Atrophy. In fact, only FOUR people worldwide are known to be diagnosed with the VRK1 variation of SMA. Learn more about VRK1 by visiting http://ghr.nlm.nih.gov/gene/VRK1.
Resources for Families
- Cure SMA
- Fight SMA
- SMA Support
- SMA Medical Supply
- Gwendolyn Strong Foundation
- Jadon’s Hope
- Jacob Isaac Rappoport Foundation
Newly diagnosed families also should also visit these sites for support and information: