Tay-Sachs Disease

An overview

Tay-Sachs disease is caused by low levels of the enzyme beta-hexosaminidase A that is needed for the brain to function properly. The deficiency is caused by a problem with the HEXA gene.

The enzyme beta-hexosaminidase A plays an important role in breaking down waste products in the brain. These waste products are called GM2 ganglioside. Some doctors and scientists refer to GM2 ganglioside as the substrate of the enzyme, meaning the substance on which an enzyme acts.

Without enough enzyme, the waste products build up and cause damage to brain and spinal cord cells (neurons or nerve cells). This causes the cells to malfunction and die.

The science

Tay-Sachs disease is caused by certain disease-causing changes in the HEXA gene. The HEXA gene is responsible for producing the beta-hexosaminidase A enzyme.

The defective HEXA gene results in two problems. Firstly, there is not enough (or any) beta-hexosaminidase A enzyme. Secondly, there is too much GM2 ganglioside in the brain and spinal cord.

The beta-hexosaminidase A enzyme is synthesised in a specialised part of the cell called the endoplasmic reticulum. It is then transported through another section called the Golgi apparatus to its site of action in the lysosome.

In the lysosome, the beta-hexosaminidase A enzyme plays a critical role in breaking down GM2 ganglioside. Remember that a ganglioside is a special type of lipid or fat that is especially found in brain cells. They are large and complex, and cannot be used by the brain as they are, but need to be broken down into smaller strands or molecules. Breaking them down is a multi-step process which results in smaller products that the brain can then recycle for other purposes.

With too little, or no, beta-hexosaminidase A enzyme, the large GM2 strands cannot be fully broken down. Instead, GM2 remains stored in the cells of the brain and spinal cord. Over time, this causes the cells to malfunction and eventually die.