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Tay Sachs disease
Introduction:
It is a fatal inherited disease of the central nervous system caused by lack of an enzyme called hexosaminidase A (hex A). The enzyme is necessarily required for metabolic breakdown of fats in brain and nerve cells. The disease appears in infants at the age of 4 to 6 month, when suddenly these healthy babies stops turning, crawling and smiling. In those infants having Tay Sachs disease, the fats gradually build up in brain and nerve cells, resulting in damage of brain and entire nervous system.
Risk Factor:
- The risk of Tay Sachs disease is higher in infants of Ashkenazi Jews (Central and Eastern European).
- Non Jewish individuals of French-Canadian ancestry (From East St. Lawrence river valley of Quebec) are also at higher risk.
- Members of Cajun population in Louisiana are also at higher risk.
- One in 30 American Jews is carrier of Tay Sachs gene.
- The disease is only transmitted through heredity.
- In a Tay Sachs carrier, one gene is normal and one Tay Sachs gene.
- The carries of Tay Sachs gene have no symptoms and leads normal healthy life.
- When both the parents are carriers of Tay Sachs gene, there is a 25% chance that baby inherits both Tay Sachs gene and thus will have the disease, a 25% chance that the baby will be normal and the rest 50% chance that the child will be carriers of Tay Sachs disease.
Types of Tay Sachs Disease:
Depending on the severity of the disease it has been divided in four types.
- Classical infantile type of Tay Sachs disease.
- Juvenile form
- Chronic form
- Adult onset forms.
The symptoms of the disease appear at different age intervals and mainly depend on the severity of the disease.
Classical Tay Sachs Disease:
- Symptoms in classic Tay Sachs disease appear at the age of 4 to 6 month of age and death occurs by the age of 5.
- In classical Tay Sachs disease, hex A enzyme is completely missing.
Juvenile Tay Sachs Disease:
- In juvenile form of the disease, low level of hex A gene is present and thus delays the symptoms.
- Symptoms appear at the age of 2 to 5 years and death occurs by the age of 15.
Chronic Tay Sachs Disease:
- In chronic form, the symptoms appear at the age of 5.
- Symptoms are milder than the juvenile form and include slurred speech, muscle weakness, tremors and unsteady gait.
Adult on set Tay Sachs Disease:
- In adult on set form, the symptoms appears later in the life.
- Symptoms are milder than the chronic form.
Prebirth diagnosis for Tay Sachs disease:
- Amniocentesis: This test is required to be carried out during 14-18 week of pregnancy. A small amount of fetal cell is collected from amniotic fluid and examined.
- Chorionic Villus Sampling (CVS): Although this test carries a small amount of risk of miscarriage. A small amount of fetal tissue is collected during 9-11 week pregnancy and tested for the risk of Tay Sachs disease.
Diagnosis for Tay Sachs carrier:
- The blood test is carried out for diagnosing the carriers of the disease.
- The blood sample is tested for hex A enzyme, carrier of Tay Sachs disease will have half the enzyme compared to a non-carrier.
- Further DNA based genetic analysis can be carried out for knowing the mutation in hex A enzyme.
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