Tay Sachs disease
Tay Sachs disease is an inherited metabolic disease (see entry Inherited Metabolic diseases). The body lacks an enzyme called hexosaminidase A (hex-A). In its absence, a lipid chemical, GM(2)ganglioside, builds up abnormally in the body. This destroys nerve cells, causing mental and physical problems.
Last updated March 2014 Dr H Mundy, Consultant in Paediatric Inherited Metabolic Disease, Evelina Children’s Hospital, London, UK.
Storage of GM(2)ganglioside begins during pregnancy. However, the baby usually develops normally until about six months of age. The nervous system becomes progressively affected and sadly the disease is usually fatal between age three to five years. The child becomes blind, deaf and unable to swallow. Muscles begin to waste and paralysis develops. Additionally, epileptic seizures may occur.
Late-onset Tay Sachs disease (LOTS) is much less common than the classical infant form. Individuals with LOTS have very reduced enzyme levels rather than complete absence.
Onset of LOTS is later and individuals vary in the way it affects them.
Tay Sachs is caused by mutations in the HEXA gene, which provides instructions for making part of an enzyme called beta-hexosaminidase A. This enzyme is located in lysosomes, which are structures in cells that break down complex molecules and act as recycling centres. Tay Sachs disease is part of a group of conditions called lysosomal storage disorders (LSDs).
Tay Sachs patients and carriers (those that carry only one mutation in the gene and are not affected by the condition) can be identified by a blood test that measures beta-hexosaminidase A activity.
There is no cure for Tay Sachs disease. Treatment involves making the child feel as comfortable as possible by treating the associated symptoms. Anticonvulsant medication may be used to control fits. Children may require supportive measures with feeding when swallowing becomes difficult.
For a number of LSDs a replacement enzyme can be manufactured to replace the missing enzyme. The enzyme replacement therapy (ERT) is usually given regularly into a vein. Enzymes are big molecules that cannot cross into the brain and so there is very limited improvement of neurological problems. Recently, trials have started for a number of neurological LSDs by infusing enzyme into the brain via the cerebrospinal fluid (CSF), though ERT is not yet available for Tay Sachs disease.
Another way to replace enzymes is to transplant stem cells – usually as an umbilical cord transplant. Transplanted cells become part of the bone marrow and are capable of making enzyme. This is highly experimental for Tay-Sachs disease, particularly the infantile form, as the disease progresses too rapidly to prevent severe neurological disease. This should never be attempted outside very experienced centres that are properly regulated.
The mode of inheritance is autosomal recessive. One in 25 Ashkenazi Jews and 1 in 250 of the general population are carriers of this disease. Carrier detection is available through genetic clinics.
It is recommended people from at risk population undergo testing before starting a family. Prenatal testing from chorionic villus sampling (CVS) during pregnancy can detect Tay Sachs disease.
Cure & Action for Tay-Sachs (CATS) Foundation
The Foundation is a Registered Charity in England and Wales No. 1144543. It was established in 2011, and provides a variety of information and support for families living with Tay-Sachs, including (but not limited to) provision of short breaks and purchase of specialist equipment. The Foundation is also actively involved in raising awareness and funding for research, and publishes a regular newsletter.
Group details last updated October 2015.