Genetic testing before pregnancy detects up to half of the risk

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.

More than 3,000 hereditary factors tested

Do these genetic tests for inherited risk factors deliver what they promise? Anita Rauch, director of medical genetics at the University of Zurich, and her team in Switzerland have now for the first time addressed this question by extensively studying the potential and pitfalls of such expanded carrier screening (ECS). To this end, the scientists tested sequence data from 700 parents who already had children with neurodevelopmental disorders. Many of the more than 3,000 investigated genes can cause intellectual disabilities, developmental disorders, autism and other disorders.

“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.

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