Tay-Sachs disease is caused by a genetic mutation in the HEXA gene on chromosome 15. This gene is responsible for producing a subunit of the hexosaminidase A enzyme. The disease is inherited in an autosomal recessive manner. Let's break this down:
Understanding the Cause
| Term | Explanation |
|---|---|
| HEXA Gene Mutation | A change in the DNA sequence of the HEXA gene. This means the instructions for building a working hexosaminidase A enzyme are faulty. |
| Chromosome 15 | The specific location of the HEXA gene within human DNA. |
| Hexosaminidase A Enzyme | This enzyme is crucial for breaking down fatty substances called gangliosides in the brain and nerve cells. When it doesn't work properly, these gangliosides build up to toxic levels. |
| Autosomal Recessive | Means a person must inherit two copies of the mutated gene (one from each parent) to develop the disease. If they only inherit one copy, they are a carrier but usually don't show symptoms. |
How It Works: A Step-by-Step Explanation
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Normal Gene Function: In healthy individuals, the HEXA gene instructs the body to create functional hexosaminidase A.
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Enzyme Activity: This enzyme breaks down gangliosides, preventing them from accumulating to harmful levels.
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Mutated Gene: In individuals with Tay-Sachs, the HEXA gene is mutated, leading to little or no production of functional hexosaminidase A.
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Ganglioside Buildup: Without the enzyme to break them down, gangliosides accumulate excessively, particularly in nerve cells of the brain.
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Cell Damage: This buildup causes progressive damage to nerve cells.
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Symptoms: The damage leads to the severe neurological symptoms characteristic of Tay-Sachs disease.
Inheritance Pattern
- Carriers: Individuals with one copy of the mutated gene are carriers. They typically show no symptoms because their one normal gene copy produces enough functional enzyme.
- Risk for Offspring: If both parents are carriers, there is a 25% chance their child will inherit two copies of the mutated gene and develop Tay-Sachs disease. There's a 50% chance the child will be a carrier, and a 25% chance they will inherit two normal genes and not be affected.
In Summary
Tay-Sachs disease arises due to a genetic defect affecting the production of a critical enzyme, which results in the accumulation of harmful substances in the brain. Understanding the autosomal recessive inheritance pattern is key to assessing the risk of passing on the mutated gene to future generations.
