A recent study reveals that gene-start regions are especially susceptible to mutations, which can be passed down to subsequent generations. Researchers have pinpointed previously overlooked areas of the human genome that are particularly prone to accumulating genetic changes, making them crucial for understanding inheritance and the development of disease.

These regions, located at the start of genes—called transcription start sites—are where DNA is first transcribed into RNA. The study, published in Nature Communications, found that the first 100 base pairs after a gene’s start have a 35 percent higher likelihood of mutation than would occur by chance.

Figure 1. Gene Start Regions Reveal Unexpected Mutation Vulnerability

“These sequences are highly mutation-prone and rank among the most functionally critical regions of the human genome, alongside protein-coding areas,” said Dr. Donate Weghorn, corresponding author and researcher at the Centre for Genomic Regulation in Barcelona. Figure 1 shows Gene Start Regions Reveal Unexpected Mutation Vulnerability.

The study also finds that many of these mutations arise shortly after conception, during the earliest cell divisions of the embryo. Known as mosaic mutations, they occur in only a subset of cells, which has made this DNA hotspot difficult to detect until now.

Parents can carry mosaic mutations that contribute to disease without exhibiting any symptoms, since the changes are limited to certain tissues. However, if these mutations are passed through egg or sperm cells, the child inherits the mutation in all cells, potentially leading to illness.

A Broad Survey of Genetic Variation in Humans

To identify this pattern, the researchers analyzed transcription start sites across 150,000 genomes from the UK Biobank and 75,000 from the Genome Aggregation Database (gnomAD), then compared these findings with data from eleven family studies detailing mosaic mutations. Their analysis showed that many gene start sites harbor more mutations than expected, with the most affected regions linked to genes involved in cancer, brain function, and limb development.

The mutations are likely deleterious. Extremely rare, recent variants were heavily concentrated near start sites, while older, more common variants showed a reduced excess, indicating that natural selection removes harmful mutations over generations. Consequently, families carrying mutations in gene start sites—especially those affecting cancer and brain-related genes—are less likely to pass them on, preventing these mutations from persisting long-term.

Preventing Misinterpretation and Revealing Overlooked Insights

The study helps prevent misinterpretations from mutational models, which geneticists use to estimate the expected number of mutations in specific genome regions under normal conditions. Clinically, these baselines guide which variants warrant attention and which can be deprioritized.

Recognizing that gene start sites are naturally mutation-prone means the true baseline in these regions is higher than previously assumed, requiring recalibration of models.

“If a model ignores that this region is mutation-rich, it might expect 10 mutations but see 50. If the true baseline is 80, then 50 is actually below expectation, indicating natural selection is removing harmful changes. You could completely miss the significance of that gene,” explains Dr. Weghorn.

The findings also impact studies focusing only on mutations present in a child but absent in the parents. While this approach works for mutations found in every cell, it overlooks mosaic mutations, which occur in only some tissues, causing potentially important disease-related information to be lost.

“There’s a blind spot in these studies,” says Dr. Weghorn. “One way to address it is by examining how mutations co-occur to detect mosaic mutations, or by revisiting previously discarded mutations near the transcription start sites of genes most affected by this hotspot.”

Uncovering a Hidden Source of Genetic Mutations

Transcribing DNA into RNA is a complex and dynamic process. The study suggests that the mutational hotspot arises because the transcription machinery often pauses and restarts near gene start sites, sometimes even moving in both directions. Meanwhile, transient structures can expose one DNA strand, making it susceptible to damage.

These factors make transcription start sites particularly prone to mutations during the rapid cell divisions following conception [1]. While cells usually repair such changes, the pressure to grow quickly can leave some mutations uncorrected, leaving lasting “scars” on the genome.

This finding fills a gap in our understanding of mutation origins. While known sources like DNA replication errors or UV-induced damage have been studied for decades, discovering a new source of mutations affecting the human germline is rare, notes Dr. Weghorn.

References:

1. https://scitechdaily.com/newly-discovered-dna-danger-zone-could-change-what-we-know-about-human-disease/

Cite this article:

Janani R (2025), Newly Identified DNA “Hotspot” May Rewrite Our Understanding of Human Disease, AnaTechMaz, pp. 634