Genes: The Building Blocks of Life
Genes are the instructions that control functions in our bodies. Every person has 20,000 genes, each made up of tens of thousands of DNA pairs for a total of 3 billion base pair. When a gene contains a mutation, it can malfunction. In some diseases, like BRCA breast cancer, if one copy of the gene has a mutation, the individual will have the disease. In other diseases, like Tay-Sachs, both copies of the gene (from the mother and father) must have a mutation to cause the disease. If only one copy has a mutation, the individual is a carrier and is healthy. But if that individual has children with another carrier, their children have a 1-in-4 chance of being affected. The individuals do not have to have the same mutation.
Mutations Are Universal
We are all born with genetic mutations, some are harmful, some are beneficial, but for many, we do not know what they do. Mutations are not related to age and everyone carries some. Most are inherited so diseases can appear more frequently in certain groups. But they appear in every other group as well. For Tay-Sachs, 1-in-30 high-risk people are carriers, but 1-in-250 people in the general population carries Tay-Sachs. This means there are over 1 million carriers in the U.S. alone, who are not high-risk and would have no reason to suspend that they are carriers.
Prenatal Genetic Tests
- In 3 billion base pair of DNA, there is a lot that can go wrong. Genetic testing does not test for everything.
- Many different kinds of mutations (deletions, additions, substitutions, etc.) can cause the same disease.
- There are over 100 different kinds of mutations that cause Tay-Sachs disease.
- For Tay-Sachs, labs can either test for changes in the blood indicative of a carrier or test for specific mutations.
- Often labs only test for 5-6 out of 100 Tay-Sachs mutations and report a “negative” result. Even the blood test is not 100% since certain mutations cause results that are hard to interpret.
Ask Your Doctor
- What tests do you recommend for me?
- What diseases do you routinely test for?
- Are there other serious genetic conditions I am at risk of passing to my child?
- How accurate are these tests? Are there other tests available?
- Can I be tested for Tay-Sachs using the blood enzyme test and DNA testing combined?