What is Spinal Muscular Atrophy?

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  • Written By: D. Jeffress
  • Edited By: Jenn Walker
  • Last Modified Date: 16 August 2019
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Spinal muscular atrophy is an inherited condition that usually becomes apparent in infancy or very early childhood. There are several types of the disease, but all cases involve the deterioration of major muscle tissue over time due to nerve cell death. The condition is progressive and ultimately fatal in most instances, but doctors may be able to provide some degree of relief from symptoms with a combination of medications, surgery, and physical therapy.

Doctors classify spinal muscular atrophy into four main types, distinguished by the specific genes they involve and the nature of the disease's progression. Type I, typically the severest form of muscular atrophy, involves an acute onset before a baby is six months old. Types II and III tend to worsen more slowly, and do not become noticeable until after the age of six months. The rarest form of spinal muscular atrophy is type IV, which entails mild, gradually worsening symptoms with an onset well into adulthood, around the age of 30.


An infant who has type I spinal muscular atrophy is likely to have very little muscle tone at birth and difficulties feeding and breathing without medical assistance. Internal structures including the heart and lungs are not strong enough to maintain involuntary reflexes, and most infants do not live past 18 months. Children with type II may have underdeveloped motor skills, difficulties sitting or standing, and frequent respiratory problems that are often fatal at some point in childhood or adolescence. The symptoms related to type III and IV spinal muscular atrophy include tremors when walking and weakness when engaging in physical activity. Type III and IV patients usually have average life expectancies.

When a doctor suspects spinal muscular atrophy based on physical symptoms, he or she can conduct a muscle biopsy to confirm degeneration and order a DNA test to check for mutated genes. Based on clinical laboratory results, specialists can confirm the type and grade of a patient's condition and determine the best approach to treatment. The progressive condition cannot be cured, and treatment is primarily designed to ease the severity of symptoms and improve patients' quality of life.

Infants with type I are usually kept in critical care hospital units for constant monitoring and treatment. Older patients typically need to take medications to manage pain and attend regular physical therapy sessions to try to build strong muscles and tendons. Scoliosis is common in patients who survive into adolescence, and corrective bracing or surgery may be necessary to prevent severe deformities. With support from doctors, counselors, and family, most people who suffer from spinal muscular atrophy come to accept their conditions and maintain positive outlooks on life.



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