Last fall I posted on Ashkenazi Jewish genetic diseases, a number of inherited diseases that occur primarily in people of AJ descent (as a result of the “ founder effect “). AJ diseases are commonly known about within the AJ community, but many non-Jewish people are completely unaware of them.
As a result of carrier screening (the ability to test parents-to-be to see if they carry a mutation for the conditions), the actual rates of individuals affected with these disease is dropping. That’s the good news. That people who are appropriate for testing don’t know about testing is the bad news. (My rant on that will have to wait until next week, when the Week of Science challenge has ended)
So here’s the skinny on how these disease are inherited, why people are “silent” carriers, and why carrier testing works:
The cells in our body typically contain 46 chromosomes. Each chromosome is a package that holds hundreds of genes. These genes contain blueprints for our growth and development; they are the instructions that make us who we are. All our chromosomes (and the genes contained in them) come in pairs. We inherit one chromosome of each pair from our mother and the other from our father.
When there is a change in a gene (a mutation), the instructions it contains are no longer correct and the gene cannot carry out its function. People affected with an Ashkenazi Jewish genetic disease have two copies of a mutation, one copy inherited from each parent. Neither gene in the pair is working correctly, which causes the symptoms of the disease.
The parents of an affected person are called “carriers.” A carrier has a mutation in one gene of the pair. Carriers are unaffected with the disease because the properly working gene is able to compensate for the gene that contains the mutation.
When two parents are carriers for a specfic Ashkenazi Jewish disease: • there is a 1 in 4 (25%) chance of having a child with the disease, • there is a 1 in 2 (50%) chance of having a child who is an unaffected carrier like the parents, • and, there is 1 in 4 (25%) chance of having a child who is unaffected and is not carrier.