21st May 2019
For many years it has been widely known that a ‘recessive’ condition, called Tay Sachs disease, is ten times more common in the Ashkenazi Jewish (AJ) population than in the wider population. Genetic screening for Tay Sachs carriers has been commonplace in the UK since it was first introduced in the 1980s. In the intervening years research has discovered several other recessive genes that are more common in the AJ population. Around the world, including in the UK, these findings led to the development of a panel test for common recessive genes, specific to the AJ population. For nearly 20 years, while working in the NHS, I was involved in the Tay Sachs screening programme, and the subsequent development of the extended panel of nine disorders.
You might remember the term ‘recessive’ if you did Biology GCSE. These are faulty genes we carry unknowingly. As all our genes come in pairs, having a recessive ‘mutation’ (like a spelling mistake in the gene code) in one half of the pair will not cause a person any health problems, so they are considered a healthy carrier. Of our 20,000 genes (each of which is an instruction telling the body how to work) we all carry half a dozen or so recessive mutations. So being a carrier of several genetic conditions is actually the normal human state, and nothing to worry about. The most important thing is to harness our understanding of genetics for good, so that people have the option to be screened for these conditions in order to help manage risk. I will come on to how we can manage these risks shortly, but first for a few other things to flag up.
The only time that being a carrier of a recessive gene matters, is if both members of a couple are carriers of the same gene. In this situation there is a 25% risk of having an affected child, if both parents pass on the faulty gene to the child.
Targeted panel tests are very useful for those with definite Ashkenazi lineage as they detect the high risk genes. This is currently offered in the UK by a community charity, Jnetics, via a clinic at Barnet Hospital. Information about how to access this test can be found at this website: www.Jnetics.org
However it is also possible for people with AJ lineage to carry other genetic conditions, that exist in all ethnic groups. Also, some people have mixed heritage with both Ashkenazi and non-Ashkenazi or non-Jewish lineage. This is why I am so pleased that here at CRGH we are now able to offer a new pan-ethnic panel test, which tests couples to identify carriers of around 600 rare, serious genetic conditions. The panel includes all the common recessive AJ genes. Although no test can guarantee a healthy baby, this new test gives a more comprehensive overview of genetic risk for future children. This test is called ‘CarrierMatch’ and more information, and booking details for this test, can be found here
There are other types of genetic risk, aside from recessive genes, and in recent years, awareness has grown regarding those genetic factors that are important in common diseases like cancer and heart disease, as well as other types of rare genetic conditions. The CarrierMatch panel does not include these kinds of genes (referred to as ‘dominant’ genes). However, if you have a personal or family history that indicates a risk of a dominant gene mutation, we can provide advice regarding genetic testing options.
Now we come to the question of how we avoid these faulty genes being passed on to the next generation, once we know that a specific faulty gene exists in a family. There are several options, some of which come into the category of avoidance eg. not having any (more) children, adoption, or using a sperm or egg donor in place of the parent carrying the high risk gene. However, for many couples these are not appealing options. Another possible solution is to conceive a pregnancy naturally and opt for prenatal diagnosis (eg. like an amniocentesis test) to diagnose if the faulty gene has been passed on to the pregnancy, allowing for termination of affected pregnancies. However for some in the Jewish community this is undesirable, especially for those who follow Orthodox Jewish law, where this may not be permissible.
So, another option to avoid passing on a known faulty gene to a child, is for the couple to have Pre-implantation Genetic Diagnosis (PGD) treatment. This is a form of IVF, which is offered to couples who have a genetic risk (and who may have normal fertility, or sometimes a fertility problem as well), so that we can create embryos in the laboratory using their eggs and sperm. We then carry out genetic testing on the embryos, in order to choose an unaffected (healthy) embryo to implant in the woman’s womb, in order to start a pregnancy that is not at risk of having the genetic condition.
Although PGD treatment is expensive, the good news is that the NHS does offer funding in many cases (although only for the couple to have one unaffected child). At CRGH we offer both self-funded and NHS funded PGD treatments, with excellent success rates. More information is available here
For CarrierMatch testing, or a private Genetic Counselling session to assess genetic risk in a family and discuss genetic testing options, or to discuss PGD treatment, appointments can be booked with Sara Levene at the CRGH.