The Guardian has learned that couples undergoing IVF in the UK are exploiting an apparent legal loophole to rank their embryos based on genetic predictions of IQ. But what is polygenic screening and does it work?
What kinds of tests can be performed on embryos in the UK?
Fertility treatments are strictly regulated, with tests performed on embryos legally restricted to a list of serious health conditions. These include about 1,700 single-gene disorders, including Huntington’s, cystic fibrosis and sickle-cell disease. Clinics can also test for aneuploidy – when an embryo has extra or missing chromosomes – which lowers the chance of a successful pregnancy or can lead to genetic conditions. Polygenic screening, or PGT-P, which aims to give predictive scores for health, height, IQ and other traits is not permitted.
Why has this grey area emerged?
As genetic sequencing has become quicker and cheaper, laboratories typically screen for aneuploidy (known as PGT-A testing) by generating a low-resolution genome sequence for each embryo. This sequence is not shared with IVF clinics – they only receive a readout of whether or not an embryo has any missing or extra chromosomes. But patients have the right to access their medical data, including information about embryos, under GDPR and the Data Protection Act 2018.
What can this data reveal about an embryo?
The sequence would reveal the sex of an embryo. When combined with high-quality genome sequences of the parents, it could also be used to generate predictions of mental and physical traits. Several US companies offer commercial health and IQ prediction services.
What is polygenic screening and does it work?
Traits such as height and intelligence are known to be partly heritable. But, unlike with a single-gene disorder, the genetic component is spread across thousands of genes that differ across people and interact with each other and the environment in complex ways.
Nevertheless, by analysing vast genetic databases, scientists have developed algorithms that give predictive scores for a host of physical and mental traits. These scores are probabilistic – an embryo with a high predicted risk of diabetes is not guaranteed to develop the condition.
Advocates of polygenic screening say parents are capable of making judgment calls on a technology that could offer health benefits. However, others say the accuracy of the predictions is untested in the context of embryo selection and its use is not justified on health grounds.
“Polygenic scores are typically very crude and only capture a tiny fraction of the heritable component of complex traits like IQ,” said Prof Frances Flinter, of Guy’s and St Thomas’ NHS foundation trust and a member of the fertility treatment regulator HFEA. “A major concern of geneticists is that the use of PGT-P represents premature adoption of inadequately validated tests.”
