| What Is Spinal Muscular Atrophy??? |
| What is Spinal Muscular Atrophy? The name Spinal Muscular Atrophy (SMA) refers to several related neuromuscular diseases that all have the same basic cause, although they differ considerably in age of onset and severity. SMA occurs in approximately 1/10,000 births, and SMA Type I, which is the most severe form of this disease, is the most common single genetic cause of death in infancy. There is currently no cure for SMA or treatment to stop its progression. Medical care and physical therapy may help prevent complications and ensure the best possible quality of life for those affected. The shared feature of all the forms of SMA is progressive muscle weakness and wasting caused by degeneration of the anterior horn cells of the spinal cord (also called the lower motor neurons). Normally these nerve cells relay messages from the brain to the muscles and stimulate them to contract. Without this stimulation, the muscles atrophy. Eventually, in addition to generalized muscle weakness and wasting, particularly in the trunk, upper arms and thighs, respiratory problems can develop. The brain and the sensory nerves that allow us to feel sensations such as temperature, touch and pain are not affected, intelligence is normal. The Types of Spinal Muscular Atrophy. There are three types of childhood Spinal Muscular Atrophy and one adult form, classified in terms of the age at which weakness becomes obvious and the severity of its progression. SMA Type I - the most severe form, is also known as Infantile Spinal Muscular Atrophy or Werdnig-Hoffmann disease. The onset of SMA TypeI is either in utero or within the first few months of life. Course: Often have severe weakness at birth requiring respiratory support and intubation; lack of normal movement and motor development; bulbar and respiratory involvement; tongue fasciculations; head control is poor; does not sit unassisted. The major management issue is the prevention and treatment of respiratory infections. Prognosis: this disease is the most common cause of genetically determined neonatal death; lifespan to 3 years possible. SMA Type II - Intermediate Spinal Muscular Atrophy or benign Werdnig-Hoffmann disease. Usually apparent within the first 6 months to 3 years of life Course: Weakness in skeletal muscles; never stand or walk unassisted; may have fasciculations in tongue or hands; may develop scoliosis or joint contractures; may require ventilator support at some time. Prognosis: Frequently live very satisfying and productive lives well into adulthood. SMA Type III - Juvenile Spinal Muscular Atrophy or Kugelberg-Welander disease. Usually apparent from 1-15 years old. Course: General weakness of skeletal muscles; walks unassisted for a period of time; wheelchair often required by age 30; scoliosis and contractures may develop; may show hand fasciculations. Prognosis: Lifespan generally unaffected. SMA Type IV - Adult Spinal Muscular Atrophy begins later in life, usually between the ages of 15 and 50. The degree of disability is often mild and life expectancy is not usually affected. Type IV is less common and less clearly understood at the present time than the three childhood forms. Prognosis: Normal lifespan. Fasciculation - involuntary twitching of muscles. Contracture - permanent tightness or shortening of a muscle due to a disease. Scoliosis - curvature of the spine. How is SMA transmitted? The childhood SMAs are caused by a genetic defect on chromosome 5 which is transmitted through a pattern of recessive inheritance. Affected children are born to parents who are both carriers, with both a normal and mutated form of the SMA gene. The mutation is harmless in carriers, but a child who inherits a "double dose" of the gene (that is one copy of the faulty gene from each parent) is born with SMA. When both parents are carriers there is a 25% risk in each pregnancy that their child will be born with the disease. SMA is a relatively common disease. An estimated one in 40 people is a carrier of SMA, so the chance of a carrier mating with another carrier is appreciable even if the disorder is completely unknown in previous generations of their families. |
| I would like to thank Melissa Richardson for her useful information. |