TAY SACHS DISEASE – ITS TRUE COLORS:

Tay Sachs disease, scientifically described as Hexosaminidase A deficiency is a genetic disorder resulting in severe physical and mental disabilities resulting in death. The cause for this genetic disorder is due to a mutation on the HEXA gene found in chromosome 15 which governs the production of gangliosides in the nerve cells. Tay Sachs is a rare disease because it is an autosomal recessive disease, meaning that the defective gene is not located in the sex chromosome and the disease can be inherited only if both the parents possess defective copies of the gene.

Tay Sachs disease (TSD) can be classified into three types depending on the time of onset of the symptoms and disorder. They are infantile TSD, Juvenile TSD and late onset TSD. The infantile form of the disease sets in after 6 months of the baby’s growth and goes on relentlessly till muscle atrophy and paralysis results in the death of the infant. The juvenile form of TSD is rare which sets in between the age of 2 and 10 during which they develop several complications of nervous function and results in death. The Late Onset TSD, abbreviated as LOTS sets in during the 20s and 30s. It is usually non-fatal and is characterized by swallowing and speech difficulties, unsteadiness of gait and neurological deterioration.

The inheritance of TSD adheres to Mendelian laws wherein the resulting child has 25% probability of acquiring the disease from heterozygous parents. The mutation of the HEXA gene results in the deficiency or failure of the body mechanism to synthesize an enzyme called Hexosaminidase A which catalyzes the breakdown of a special class of lipids called GM2 gangliosides. This therefore leads to accumulation of gangliosides in the neurons in the patient’s brain and interferes which its normal functioning.

There are over 100 possible mutations which can occur in the HEXA gene which encode for the Hexosaminidase A enzyme. Some of the mutations are widely expressed in specific human populations for over hundreds of years. The most notable example is the Ashkenazi Jewish population who carry a mutation 1278insTATC resulting in alteration of the messenger RNA. Apart from being directly affected by Tay Sachs disease, a majority of children born to parents with either of them possessing a defective HEXA gene can be potential carriers of the gene without being affected by the disease.

There is also another scenario wherein a child may inherit two different types of HEXA mutations which attenuate the biodegradation of gangliosides in varying degrees. Thus the afflicted individual may not have completely lost Hexosaminidase A activity. This type of a carrier is called a Compound Heterozygote.

With significant advancements in medical diagnosis and prenatal care, several measures have been introduced to prevent the spread of Tay Sachs Disease to other populations. The primary methods of preventing onset of TSD is by screening potential carriers of the defective HEXA gene and counseling them whether or not to give birth to infant. The other measure adopted is prenatal testing by which tests are conducted in the developing foetus by sampling the amniotic fluid or the chorionic villus. Biomedical and enzyme assays are also available to diagnose people affected by TSD by estimating the activity of the Hexosaminidase A enzyme.