Preimplantation genetic testing, the screening of IVF embryos before implantation, was built to catch single-gene disorders such as cystic fibrosis and haemophilia. In a new article in Frontiers in Reproductive Health, Professor Tetsuya Ishii of Hokkaido University argues that the technology has quietly outgrown that purpose and is now being used to estimate an embryo's chances of developing complex conditions later in life, including Alzheimer's disease, diabetes and heart disease, as well as traits like intelligence.
The distinction matters. A mutation in a single gene can make a disease close to inevitable, and testing for it produces a clear yes or no. Polygenic traits work differently: hundreds or thousands of genetic variants each nudge the odds slightly, and lifestyle and environment do much of the rest. Schizophrenia, cancer, physical appearance and intelligence all fall into this category. A polygenic score for an embryo is a probability shaped by incomplete information, not a diagnosis, which makes it a shaky basis for choosing one embryo over another.
For families with Alzheimer's in their history, the appeal is obvious, and so is the problem. Late-onset Alzheimer's is influenced by many genes plus decades of environmental exposure, so selecting an embryo on a risk estimate offers no guarantee about a life that will unfold seventy or eighty years from now. Ishii's concern is that once screening extends to socially valued characteristics rather than serious inherited illness, the line between preventing disease and selecting for preferred children becomes hard to defend.
The scale gives the argument weight. The International Committee for Monitoring Assisted Reproductive Technologies estimates more than 10 million people worldwide have been born through IVF and related techniques over four decades, so any shift in what these clinics routinely offer reaches a large population. Ishii calls for stronger oversight and clearer rules governing how embryo genomic testing may be used.