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Tay-Sachs Disease

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on September 1, 2009 at 2:52:50 pm
 

 Tay-Sachs Disease

 

Tay-Sachs disease is an autosomal recessive disorder. It is a mutation in the HEXA gene on the long arm of chromosome 15. It is common in the Ashkenazi-Jewish population, approximately 1:3600 births, with a carrier frequency of 1:30 (medical genetics) and a higher incidence among a number of other population groups. 

 

The HEXA gene encodes for β-Hexosaminidase A, an enzyme responsible for the breakdown of the fatty substance ganglioside GM2, which is found in the brain (family genetic). This mutation of the HEXA gene causes an insufficiency in the concentration of this enzyme in the body of the affected person. This enzyme deficiency allows GM2 to build up in excess amounts in the lysosomes of the neural cells. This causes neuro-degeneration, resulting in a range of progressive symptoms. There are 3 types of Tay-Sachs; infant, juvenile and chronic adult-onset, with infant being most prevalent. 

 

Symptoms first appear in infants around the age 2-6 months, with normal development up until then. As it is a neurodegenerative disorder, the first symptoms are a decline in general motor skills and muscle weakness. It becomes difficult for the child to hold their head up, with many other problems presenting. These include blindness, poor feeding, lethargy, hypotonia (low pressure in the intraocular fluid), hyperreflexia (increased activity of the physiological reflexes), opisthotonos (a spasm of the muscles in which the head and lower limbs are thrust forward, and the spine is arched), hyperacusis (exceptional hearing), deafness, spasticity, myoclonic seizures (atlas). A major indicator of TS is a cherry read spot on the fovea centralis of the macula in the eye (atlas). The spot indicates the destruction of ganglion cells in the foveal area, with the remaining cells filled with ganglioside (atlas). 

 

The HEXA gene (15q23-q24) has been identified to have over 100 mutations to date (atlas) in relationto Tay-Sachs. There are certain mutations associated with particular populations.

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