About Recessive Disorders
Autosomal recessive inheritance occurs when alterations in both copies of an inherited gene pair are required to cause a genetic disorder. With recessive inheritance, a single normal copy of a gene appears to compensate for the mutated one, to prevent the disorder developing.
When both partners in a couple are carriers, their children will have a 25% chance of inheriting the disorder, a 50% chance of becoming carriers and a 25% chance of inheriting both normal copies of the gene. The same risk applies to each conception, regardless of the outcome of previous conceptions.
There is typically no “family history” with autosomal recessive disorders since these conditions require both parents to be carriers. Tay-Sachs disease is an example of a recessive disorder.
All the disorders covered on the Jnetics carrier test are inherited in a recessive manner.
In X-linked disorders, there is a mutated gene on the X chromosome. Unlike autosomal inheritance, the possibilities of having affected children depend on which parent transmits the altered gene.
Males receive a Y chromosome from their father and an X chromosome from their mother, whereas females receive an X chromosome from both parents. Men are affected by X-linked disorders because they have only one copy of the X chromosome and have no “backup” copy to make the necessary protein product. Women who have one mutated copy of the gene tend to be unaffected because their one functional copy compensates for their non-functional one.
The only X-linked genetic disorder we offer testing for is Fragile X syndrome. Testing for Fragile X is offered as an optional add-on for women screening through the Jnetics clinic. It is not one of the 47 disorders covered on the test offered to sixth form and university students.