Genetic Testing Before Pregnancy Detects up to Half of the Risk
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- 01 Sep 2022
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Are would-be parents carrying a genetic risk of serious illnesses that they could potentially pass on to their children? In the USA, doctors recommend that couples have genetic screening before trying to conceive. Researchers at the University of Zurich have now shown that a maximal variant of this test detects the risk in 44 percent of couples who are related by blood, and in just 5 percent of other couples. Non-hereditary newly acquired mutations are a major reason for the reduced detection rate in the latter.
The use of biomarker and genetic tests during pregnancy is now extremely widespread. But what if both parents’ genes were broadly analyzed for possible risks prior to conception? Are there any rare hereditary diseases in the genome that the father and/or mother are unknowingly carrying? If both parents have the same genetic defect in their genes and both pass this on to their child, this will often cause the child to have a serious illness.
In many parts of the US, broad genetic testing is offered to prospective parents and is usually also recommended in early pregnancy. The screenings predominantly indicate recessively inherited genes that are non-gender specific - in other words, those that have an effect only if both gene copies carry a mutation. Recessive genes on the X chromosome are a special case, whereby healthy mothers can pass this gene onto their children. However, normally only sons suffer from the consequences this mutation as they carry only one X chromosome and therefore do not have a second gene copy to compensate for the defect.
"In our study, we were able to show that this type of broad genetic testing can detect the risk of the child having a severe developmental disorder in about 44 percent of cases if the parents are related by blood - for instance as first or second cousins," says Anita Rauch. In some population groups this is quite common, for example in the Middle East or North Africa.
Gaps in risk detection for non-consanguineous couples in particular
The test still detected about 5 percent of cases in couples who were not blood related - but only if all known recessive genes were investigated. According to the recommendations in the US however, non-consanguineous couples should only be tested for common genes that are known to have a certain carrier frequency in the population. "Following the US recommendation would more than halve the risk detection rate, because rarer genes also play a part here," explains Rauch.
For children of non-consanguineous couples, a significantly higher proportion of developmental disorders are caused by non-hereditary de novo mutations, whereas in children of parents who are related to each other hereditary gene defects play a distinctly greater role. For this reason, the researchers state that the likelihood of detecting risks by analyzing the parents’ genes is limited for non-consanguineous couples. Read More…
