Genetics and Classification of Tay Sachs Disease

Filed under: Tay Sachs Disease - 14 Aug 2012  | Spread the word !

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Tay Sachs is a form of fatal genetic lipid storage disorder where harmful amounts of a fatty substance known as ganglioside GM2 build up in a person’s nerve cells and tissues in their brain. The condition is caused by a lack of sufficient activity on the part of an enzyme known as beta-hexosaminidase A which catalyses the biodegradation of acidic fatty materials such as gangliosides.


Infantile Tay Sachs Brain Damage

Infants with Tay Sachs disease seem to develop as usual during the first few months of their lives. Nevertheless, as their nerve cells become clogged with fatty material, a process of deterioration involving their mental and physical ability happens.

Genetics of Tay Sachs

Tay Sachs is an autosomal recessive genetic disorder. This means that when both parents are carriers there is a 25% risk of giving birth to an affected child with each pregnancy. Thus, the affected child would have received a mutated copy of the gene from each parent. If only one parent passes the defective gene to the child, the child is called a carrier. He or she won’t be sick, but will have potential to pass the disease to his or her own children, as shown in the diagram below.


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These genetic mutations have included single base insertions and deletions, splice phase mutations, missense mutations, and other more complex patters. Each of these mutations alters the gene’s protein product, sometimes severely inhibiting its function.

Classification of Tay Sachs Disease

Tay Sachs has been classified into infantile, juvenile and adult forms, depending on the symptoms and when they first appear. Most people with Tay Sachs have the infantile form. Here are the main features of each type of Tay Sachs.

1. Infantile Tay Sachs Disease. Babies with Tay Sachs appear to develop normally for the first six months after birth. As neurons become distended with gangliosides, a relentless deterioration of mental and physical abilities begins. The child becomes blind, deaf, unable to swallow, atrophied, and paralytic.

2. Juvenile Tay Sachs Disease. This form is rarer than other forms of Tay Sachs, and usually is seen in children between two and ten years old. People with Tay Sachs develop cognitive and motor skill deterioration, dysarthria, dysphagia, ataxia and spasticity. They typically die between five and fifteen years old.

3. Adult/Late-Onset Tay Sachs Disease. This is one of the rarest forms of the disease, because its symptoms begin to show at the age of 30 or 40. In contrast to the other forms, late-onset Tay Sachs disease is not fatal as the effects can stop progressing.

Treatment of Tay Sachs


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Unfortunately, medical science has not yet come up with a cure for Tay Sachs. Researchers are pursuing a number of approaches of trying to find a cure for the disease. A possible treatment would consists in enzyme replacement therapy to provide the Hex-A that babies with Tay Sachs disease lack. Bone marrow transplantation has been attempted, although it has not been successful to date in either reversing or slowing down the damage done to the nerves.

 

There is no known way of preventing this terrible disorder. Genetic testing can detect if you are a carrier of the gene for this disorder. If you or your partner are from an at-risk population group, it is recommended that you undergo testing before starting a family. Testing the amniotic fluid can diagnose Tay Sachs disease in the womb.

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