About SMA

What Causes Spinal Muscular Atrophy?

 Spinal Muscular Atrophy is an autosomal recessive disease, which means that both parents must be carriers. Both parents must have the gene responsible and these genes must be passed onto their child. When a child has received this gene from each of its parents it will than 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%, or 1 in 4.

Familial Forms (affecting other family members) of Spinal Muscular Atrophy in the older age group can occur as autosomal recessive, mutants or autosomal dominant. The genetic defects underlying these diseases make it necessary to be precise regarding the inheritance pattern in a particular family.

Quick Facts about Spinal Muscular Atrophy


Spinal muscular atrophy (SMA), the number one genetic killer of children under the age of two, is a group of inherited and often fatal diseases that destroys the nerves controlling voluntary muscle movement, which affects crawling, walking, head and neck control, and even swallowing.


SMA is one of the most prevalent genetic disorders.  One in every 6,000 babies is born with SMA. Of children diagnosed before age two, 50 percent will die before their second birthday. SMA can strike anyone of any age, race or gender. One in every 40 people carries the gene that causes SMA. The child of two carriers has a one in four chance of developing SMA.


Type 1, or Werdnig-Hoffmann Disease, is the most severe form of SMA. Children with Type I tend to be weak and lack motor development, rendering movement difficult. Children afflicted with Type I cannot sit unaided and have trouble breathing, sucking and swallowing. Type I SMA strikes infants between birth and six months.

Type II is slightly less severe. Type II patients may be able to sit unaided or even stand with support and usually do not suffer from feeding and swallowing difficulties. However, they are at increased risk for complications from respiratory infections. Type II SMA affects infants between seven and 18 months old.

Type III, also known as Kugelberg-Welander Disease, is the least deadly form of childhood-onset SMA. Type III patients are able to stand, but weakness is prevalent and tends to eventually sentence its victims to a wheelchair. Type III SMA strikes children after the age of 18 months, but can surface even in adulthood.

Type IV is the adult form of the disease in which symptoms tend to begin after age 35. Symptoms usually begin in the hands, feet and tongue, and spread to other areas of the body.

Adult Onset X-Linked SMA, also known as Kennedy's Syndrome or Bulbo-Spinal Muscular Atrophy, occurs only in men. Facial and tongue muscles are noticeably affected. In addition, these men also often have breast enlargement known as gynecomastia. Like all forms of SMA, the course of the disease is variable, but in general tends to progress slowly.

SMA does not affect sensation and intellectual activity in patients. It commonly is observed that patients with SMA are unusually bright and sociable.

What Is Spinal Muscular Atrophy?

Spinal Muscular Atrophy (SMA) is a 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 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 in patients with Type I and some patients with Type II. The senses/feelings are normal as is intellectual activity. In fact it is often observed that patients with SMA are unusually bright and sociable.

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