Genetic Diseases


Tay Sachs Disease

A few words about Tay-Sachs Disease

Tay-Sachs Disease is one of the most lethal genetic disorders The causes of Tay Sachs disease lie in a mutation in a single gene (monogenic genetic disease). The mutation that is responsible for the disease lies in the gene Hex A. This gene codes for the enzyme hexaminidase A and is found in the chromosome 15. The normal protein catalyzes the degradation of some fatty acids called gangliosides. The most important ganglioside for Tay-Sachs is the Ganglioside GM2. This material is found in the nerve cells of the brain and especially in the cell membranes. In the case of Tay-Sachs Disease there is no enough activity of the enzyme and the gangliosides are accumulated with destructive results.

Answering to the question whether there is only one specific mutation that leads to Tay Sachs or not, we have to say that the mutations can happen to more than one site of the gene. A large number of HEXA mutations have been discovered, and new ones are still being reported. These mutations reach significant frequencies in several populations.

Symptoms of Tay-Sachs

The birth of a newborn with Tay-Sachs seems to be normal and the first symptoms appear in the age of 4-6 months. The accumulation of GM2 in the nervous tissue causes a gradual destruction of the nervous system. The apparently healthy baby gradually stops laughing, crawling, smiling, grasping, turning around. Later people with Tay-Sachs becomes blind and paralyzed and unable to shallow and contact with its surrounding. One of the most common symptom is a red spot in the eyes. The death seems to be fatal (in the classic Tay-Sachs Disease) and comes in the age of 5. There are some other rare forms of the disease that happens in patients in the age of 20 or 30 (Adult Tay-Sach). These patients face a gradual deterioration of the nervous system, dysarthria, psychosis, spasticity and cognitive decline. Finally there is an extremely rare occasion of the Juvenile Tay-Sach Disease which presents in children between 2 and 10.

Tay-Sachs Transmission and Inheritance

The spread of Tay-Sach Disease happens through heredity. The carriers of Tay-Sachs have one normal Hex A gene and one Tay Sachs gene (mutated). The carriers live normally without health problems. The real patients have two Tay Sachs genes (one in each chromosome 15) and can’t escape from their tragic fate. If both carriers are parents then there is 1/4 possibility of having a child with Tay-Sachs Disease, 2/4 possibility of having a child-carrier and 1/4 possibility of having a child with no Tay-Sachs gene. If only one parent is a carrier then there is no possibility of giving birth to a newborn with Tay-Sachs but there is a 1/2 possibility of newborns-carriers. This is how Tay-Sach is transmitted (autosomal recessive pattern).

How Tay Sachs is Inherited

Tay-Sachs Prenatal Diagnosis

Considering that – tragically- there is no cure for Tay-Sachs Disease we can understand that Prenatal diagnosis is almost necessary in the case of parents that are both carriers. The prenatal Diagnosis can show whether the fetus has inherited a defective copy of the gene from both parents. If the embryo has two Tay-Sach Gene, the selective abortion seems to be the only solution – but not such an innocent one. Of course selective abortion is a matter for much further conversation as it raises many ethical issues.

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