Carrying a Recessive Disease Gene May Affect Health and Reproduction, Study Finds

Carriers of recessive disease-causing genes appear to be slightly less healthy and have fewer children on average, suggesting that even hidden genetic risks may be subject to natural selection. The effect appears strongest for genes linked to intellectual disability and is reflected in shorter education and higher rates of childlessness.

These findings come from researchers at Radboud University Medical Center, who analyzed large-scale genetic and health data. Their work challenges the traditional view that carriers of recessive disorders are completely unaffected and play a neutral role in evolution.

Unexpected patterns in intellectual disability

The new study builds on a 2014 Nature paper by the same group, which showed that most severe intellectual disabilities result from spontaneous, or de novo, mutations. These are genetic changes that arise in the child and are not found in either parent, even though each child typically carries about 100 new mutations.

In that earlier work, the team expected many cases to be caused by recessive mutations, where both copies of a gene must be faulty before a disorder appears. Instead, they found relatively few children with two damaging copies in recessive genes, despite there being more known recessive than dominant intellectual disability genes.

This mismatch raised a key question: if recessive mutations are so common in the population, why are there so few patients with two copies of them? The new research, published in Nature Human Behaviour, set out to trace what happens to these recessive variants over generations.

Carriers are not fully unaffected

To explore this question, the scientists turned to the UK Biobank, a major biomedical database containing genetic and health information from more than 500,000 volunteers. They examined data from over 300,000 participants who had both genome sequencing and detailed medical records available.

The team focused on 1,900 genes known to cause recessive disorders when both copies are mutated. They found that each person carried, on average, two clearly damaging mutations across this set of genes, meaning that nearly everyone is a carrier of at least one serious recessive disease-causing variant.

Contrary to textbook assumptions, carriers were not entirely unaffected at the group level. Compared with non-carriers, they had a slightly higher number of medical diagnoses and a marginally lower number of children, suggesting a small but measurable fitness disadvantage.

Intellectual disability genes stand out

When the researchers looked specifically at genes associated with recessive intellectual disability, the pattern became more pronounced. Harmful variants in these genes were underrepresented among adults in the Biobank compared with what would be expected by chance.

The analysis also showed that carriers of recessive intellectual disability variants tended to leave education earlier than others. On average, they reported fewer years of schooling, a proxy for lower educational attainment, despite not having a diagnosed intellectual disability themselves.

In addition, these carriers were more likely to be childless or to have fewer children. The combination of lower educational attainment and reduced reproductive success points to a subtle but consistent form of selection acting against these variants, even when only one copy is present.

Darwinian and sexual selection today

The findings align with Charles Darwin’s ideas about natural and sexual selection. In his 1859 work on natural selection, Darwin emphasized traits that promote survival. Later, in 1871, he highlighted sexual selection, in which traits affecting attractiveness and partner choice can also shape evolution.

The study authors suggest that sexual selection may be part of the explanation for the lower reproductive rates seen in carriers of certain recessive variants. Sociological research has repeatedly linked education, income and health status to partnership formation and family size.

Although the study cannot prove cause and effect for each social factor, the overall pattern is consistent with carriers experiencing a mild disadvantage in both health and reproductive success. Over many generations, such disadvantages can reduce the frequency of harmful mutations in the population.

Evolution has not paused in modern humans

The work challenges the notion that modern medicine and living conditions have largely halted human evolution. While healthcare allows many individuals with serious conditions to survive and reproduce, broad population-level data suggest that selection is still operating, albeit subtly.

Researchers emphasize that the disadvantages for carriers are small and only become visible in very large datasets. For any individual, being a carrier does not necessarily mean experiencing noticeable health problems or difficulty having children, but small statistical effects can add up across millions of people.

The authors argue that genetics textbooks may need updating to reflect that carriers of recessive disorders are not completely neutral in evolutionary terms. Instead, human genomes remain dynamic, with mutation and selection continuing to reshape the genetic landscape.

Looking ahead, the team plans to investigate how these patterns play out in populations beyond the predominantly European-ancestry UK Biobank. As more large-scale biobanks emerge worldwide, scientists expect to refine estimates of how strongly different classes of genes are shaped by ongoing selection.