Tay-Sachs disease (TSD) is a rare neurodegenerative lysosomal storage disorder (LSD) in which the child has deficiency of an enzyme hexosaminidase A (Hex-A). This causes abnormal and excessive accumulation of sphingolipids known as gangliosides in the brain and nerve cells (neurons) causing dysfunction of the central nervous system and progressively destroys the neurons.
TSD is very rare in the general population. The frequency of the condition is much
higher in Ashkenazi Jews of Eastern European origin than in others. It affects males
and females in equal numbers.
TSD results from changes (mutations) of the HEXA gene, which regulates production
of the Hex-A enzyme. TSD only occurs when both parents carry a defective copy of
TSD gene and each parent transmits the defective gene to their child. A child
who inherits the TSD genes from both parents produces defective Hex-A enzyme and
will develop TSD A person with only one TSD gene will be perfectly healthy, but
will act as a TSD carrier When both parents are carriers, there is a: 25% chance,
with every pregnancy, of having a child with TSD 50% chance, with every pregnancy,
of having a child who is a carrier When only one parent is a carrier, the child
will be completely normal
Signs and symptoms:?
A baby with TSD appears healthy at birth, but seems to be developing normally for
a few months. Though the degradation of the CNS begins at the foetal stage, observations
such as loss of peripheral vision and motor co- ordination are not seen until about
6 months of age. While symptoms vary from one child to the next, there is always
a regression of development,hyperacusis and spasticity.
Diagnosis of TSD is confirmed by a thorough clinical evaluation and specialized
tests, such as blood tests that measure the levels of Hex-A enzyme in the body.
A blood test known as carrier screening identifies TSD carriers and non-carriers.
Without carrier screening, it can remain hidden in a family for decades, surfacing
unexpectedly in the child.
There is no specific treatment for TSD. Treatment is directed toward the specific
symptoms that are apparent in each individual. Anticonvulsants may be used to treat
seizures associated with some cases of TSD. Other supportive treatment includes
proper nutrition and hydration. Genetic counseling may be of benefit for affected
individuals and their families.
Couples who are both carriers of the disease should seek genetic counseling to understand
the various choices available to them while planning a family. Prenatal diagnosis
early in pregnancy will reveal if the foetus has TSD. At-risk couples can choose
from two procedures: amniocentesis, done around the 16 th week of pregnancy, and
chorionic villus sampling (CVS), performed between the 10 th to 13 th weeks.
Tay-Sachs Disease: Genetic Home Reference. NIH. U.S. National Library of Medicine.Available
online at https://ghr.nlm.nih.gov/condition/tay-sachs
- disease. Last accessed in
April 2016. 2 Mistri M, Tamhankar PM, Sheth F, Sanghavi D, Kondurkar P, et al. Identification
of Novel Mutations in HEXA Gene in Children Affected with Tay Sachs Disease from
India. PLoS ONE 2012. 7(6): e39122. 3 Tay-Sachs Disease: National Tay-sachs and
Allied Diseases, Association of Delaware Valley. Available online at: taysachs_disease.php. Last accessed in April 2016.