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Spinal Muscular Atrophy, What Parents Should Know


If you were asked which genetic disease is the number one cause of death among babies in the United States, chances are spinal muscular atrophy would not come to mind. Yet many people may now learn more about the incurable disease because of a 5-month-old girl named Avery, and her parents’ attempts to fulfill their daughter’s bucket list.

Many people carry the spinal muscular atrophy gene

Spinal muscular atrophy (SMA) is a group of diseases that impact the motor neurons of the brain stem and spinal cord. When these motor neurons do not function properly, muscle cells also fail to function, and these cells then atrophy (get smaller) and cause muscle weakness.

Atrophy and death of motor neurons in the brain stem and spinal cord lead to weakness of the muscles involved in breathing and swallowing, and also the limbs. Spinal muscular atrophy occurs in an estimated 1 in 6,000 to 1 in 20,000 births.

What many people do not realize is that about 1 in 40 adults carry the gene for spinal muscular atrophy. According to Families of SMA, 7.5 million people in the United States are carriers.

If both a man and woman have the gene, there is a 25% chance their children will manifest spinal muscular atrophy. In the case of Avery’s parents, Laura and Mike Canahuatis, both are carriers of the gene.

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The gene referred to is the survival motor neuron gene 1 (SMN1), which is responsible for the production of a protein necessary for motor neurons. SMA is caused by a mutated or missing SMN1 gene, which leads to lack of the critical protein.

Avery’s parents have started a blog, entitled “Avery’s Bucket List,” which is written from the child’s perspective. While the bucket list includes typical milestones such as a first tooth and a first birthday party, the last item on the list—overcoming SMA—is one Laura and Mike Canahuatis know they will not fulfill. But they do hope their story will raise awareness of SMA and help lead to a cure.

Types of spinal muscular atrophy
Spinal muscular atrophy has been classified into four types, of which the first two are the most common.

  • Type I, also known as Werdnig-Hoffman disease, is the most severe form. It typically appears in infants between birth and six months of age. Avery was diagnosed with Type I SMA. Babies with Type I SMA cannot sit without support. Most die by age 2 years.
  • Type II typically affects infants between the ages of 7 and 18 months. Children with type II SMA may be able to sit without assistance or stand with support, and they are at great risk from respiratory infections. Life expectancy is limited, and some individuals reach adolescence or early adulthood.
  • Type III, also known as Kugelberg-Welander disease, is the least deadly form of childhood-onset SMA. This form may strike in children as young as 18 months, but it can also appear during adolescence. Children with Type III SMA are able to walk, but most eventually require use of a wheelchair. Complications include scoliosis and chronic shortening of the muscles around the joints. Lifespan can be normal with proper care.
  • Type IV SMA is the adult form of the disease. Symptoms typically first appear after age 35.

Spinal muscular atrophy does not affect a person’s ability to feel sensations in the face, arms, or legs, and it has no impact on intelligence. In fact, Families SMA notes that many doctors who have worked with children with SMA “are impressed that these children tend to be unusually alert, interactive, and socially gifted.”

Little Avery’s parents are making an attempt to expose their daughter to as much of life as possible in the short time she has to share with them. Already she cannot move her legs, and she will eventually need a respirator to breathe.

For more information about spinal muscular atrophy, you can contact Families of SMA, Fight SMA, and Spinal Muscular Atrophy Foundation.

ABC News
Families of SMA
National Institute of Neurological Disorders and Stroke