Summary: New research shows that carriers of recessive pathogenic gene variants—individuals who carry a single mutated copy of a gene—are not always unaffected. Analysis of more than 300,000 people reveals subtle but measurable disadvantages among carriers: an increase in medical diagnoses, slightly reduced reproductive success, and, for carriers of genes linked to intellectual disability, shorter educational careers. These findings challenge the long-standing assumption that heterozygous carriers of recessive disease genes experience no fitness consequences.
The study suggests that natural and sexual selection continue to act on human genetic variation, even in modern populations. While a single copy of a recessive mutation does not produce the disorders seen in bi-allelic cases, carriers as a group appear to have lower rates of passing these variants to the next generation than previously thought.
Key Facts:
- Hidden impact: Carriers of recessive disease variants show a higher burden of medical diagnoses and slightly lower reproductive success as a group.
- Educational effect: Carriers of variants in genes associated with intellectual disability have fewer years of formal education on average.
- Selection pressures: Subtle health, cognitive, or social effects in carriers may reduce mating opportunities or parental success, consistent with sexual selection contributing to observed patterns.
Source: Radboud University
Main finding: Carriers of recessive pathogenic variants are, on average, slightly less healthy and have a reduced likelihood of having children. The effect is particularly pronounced for carriers of variants in genes that, when mutated on both copies, cause intellectual disability.
Researchers from the Department of Human Genetics at Radboudumc revisited a long-standing genetic assumption. A 2014 study by the same team showed that most cases of intellectual disability in children could be traced to spontaneous (de novo) dominant mutations—changes that appear newly in the child and are not inherited from either parent. Each child typically acquires around one hundred spontaneous mutations in their genome, but only a tiny fraction affect genes that can cause intellectual disability. That finding raised a question: if many recessive genes exist that can produce intellectual disability when mutated on both copies, why were so few affected children explained by inherited recessive mutations?
Investigating the missing recessive variants
To address this, the team analyzed genetic and health data from the UK Biobank, examining 378,751 unrelated European individuals for pathogenic heterozygous variants in 1,929 genes known to cause recessive conditions when bi-allelic. They found that, on average, each person carries about two pathogenic variants across those recessive genes. Textbook genetics would predict carriers are phenotypically unaffected, but the population data told a more nuanced story.
As a group, carriers of these recessive variants had more recorded medical diagnoses and slightly fewer offspring. Variants in constrained genes—genes intolerant to loss of function—showed the clearest signals of reduced fitness in heterozygous carriers. Most strikingly, variants in genes associated with intellectual disability were underrepresented as bi-allelic cases in the population, consistent with selection acting against transmission.
Education and reproductive outcomes
Carriers of intellectual-disability–related variants attended school for fewer years on average, implying a modest reduction in educational attainment even in heterozygous carriers. The study also documented higher rates of childlessness among these carriers. Together, these findings imply that carriers are slightly less likely to pass on the implicated variants, which helps explain why bi-allelic intellectual disability is rarer than expected relative to other recessive disorders.
The pattern is consistent with the combined action of natural and sexual selection: beyond survival and health, social and mating factors influence which individuals reproduce. If carrier status subtly reduces social or cognitive traits valued in mate selection or parenting capacity, those variants will be transmitted less often at the population level.
Implications for evolution and genetics
This work demonstrates that selection can act on heterozygous carriers of recessive pathogenic variants across a broad range of genes and conditions. It challenges the simplified textbook view that recessive carriers are universally neutral and highlights that the human genetic landscape remains dynamic. The authors emphasize that modern medicine and social changes do not freeze evolutionary processes; instead, genetic architectures continue to shift generation to generation.
As the investigators note, we are unlikely to ever be genetically optimized for future environments; evolutionary change persists as long as mutations arise and selection—both natural and sexual—operates on phenotypes that affect survival and reproductive success.
About this evolutionary neuroscience and genetics research news
Author: Pieter Lomans
Source: Radboud University
Contact: Pieter Lomans – Radboud University
Image: The image is credited to Neuroscience News
Original Research: Closed access. “Reproductive and cognitive phenotypes in carriers of recessive pathogenic variants” by Christian Gilissen et al., Nature Human Behavior. DOI: 10.1038/s41562-025-02204-7
Abstract
Reproductive and cognitive phenotypes in carriers of recessive pathogenic variants
The distribution of human Mendelian disease alleles is shaped by mutation and selection. While selection on heterozygotes is well documented for autosomal-dominant disorders, evidence that carriers of pathogenic variants for recessive conditions experience fitness effects has been limited. In this large study of 378,751 unrelated European individuals from the UK Biobank, heterozygous pathogenic variants in 1,929 recessive disease genes were evaluated. The authors report signals consistent with fitness consequences in carriers, particularly for variants in constrained genes and for those underlying intellectual disability. Population-level reproductive effects are apparent, and variants linked to intellectual disability are associated with lower educational attainment in carriers. The observed threefold reduction in the calculated frequency of bi-allelic intellectual disability compared with other recessive disorders supports selection acting on these variants at the population level.