We all have about 23,000 pairs of genes in our bodies. Our genes are inherited and they give our bodies instructions on how to grow and function. All of the conditions that are tested for are inherited in the same pattern – autosomal recessive inheritance. This means that you have to have two changed copies of the same gene in order to have the condition.
Testing for the Ashkenazi Jewish genetic conditions is looking to see whether someone is a carrier of any of these conditions. Carriers have one changed copy of a gene and one normal copy of a gene. Carriers are healthy and do not have any symptoms of the condition but are at risk of passing it on to their children. We inherit our genes from our parents – half from our mother and half from our father. When one of parent is a carrier of TSD, each child they have has a one in two or 50% chance of being a carrier of TSD. If only one parent is a carrier of a genetic condition such as TSD, they cannot have a child affected by the condition.
When both of the parents are carriers of TSD, each child they have has a one in four (or 25%) chance of having two correct copies of the HexA gene, a one in two (or 50%) chance of being a carrier of TSD and a one in four (or 25%) chance of being affected with TSD.