Rare genetic disorders much more common than scientists thought, study reveals

LONDON — A new study has uncovered a startling revelation: rare genetic disorders caused by repetitive DNA sequences may be up to three times more prevalent than previously estimated. This discovery could dramatically reshape our understanding of these conditions and how we approach genetic testing and counseling.

Researchers from Queen Mary University of London and the Icahn School of Medicine at Mount Sinai analyzed the genomes of over 82,000 individuals, making it the largest study of its kind. They focused on repeat expansion disorders (REDs), a group of inherited neurological conditions that occur when short repetitive DNA sequences in specific genes expand beyond a normal range. These disorders include well-known diseases like Huntington’s disease and certain types of muscular dystrophy.

Published in Nature Medicine, the study utilized advanced genetic sequencing techniques to detect these expanded repetitive sequences across multiple genes associated with REDs. The team’s findings challenge long-held assumptions about the rarity of these disorders and their distribution across different ethnic groups.

“This very important advance may indicate that REDs like Huntington’s disease are nearly three times more common than we think, meaning we’re underdiagnosing these conditions,” says lead researcher Dr. Arianna Tucci, Clinical Reader in Genomic Medicine at Queen Mary University of London, in a statement. “Alternatively, the presence of certain DNA repeats may not lead to illness in some people. This could herald a major shift in how we think about genetic testing, profiling and counseling.”

One of the most striking discoveries was that approximately one in 283 individuals in the study carried a fully expanded repeat that could potentially cause disease. This is significantly higher than previous estimates, which suggested these disorders affected roughly one in 3,000 people worldwide.

The researchers also found that about one in 64 people carried a “premutation” – a moderate expansion that doesn’t cause disease in the carrier but could expand further and cause disease in future generations. This finding has important implications for genetic counseling, as it suggests that more people than previously thought may be at risk of passing these disorders to their children.

Interestingly, the study revealed that while some REDs are more common in specific populations, most were present across all major ethnic groups examined. This challenges the notion that certain REDs are exclusive to particular populations and suggests that diagnostic testing should be more widely available regardless of a patient’s ethnic background.

For example, a genetic mutation associated with a form of ALS (amyotrophic lateral sclerosis) and frontotemporal dementia, previously thought to be primarily found in Europeans, was detected in individuals of African and South Asian ancestry. This finding underscores the importance of diverse representation in genetic studies and the need for more inclusive diagnostic approaches.

The research team used sophisticated modeling techniques to estimate how many people might actually be affected by these disorders based on the genetic data. Their models suggested that the number of individuals with symptoms of REDs could be two to three times higher than current clinical observations indicate.

This discrepancy between genetic prevalence and clinical diagnosis could be due to several factors. Some individuals with the expanded repeats may have mild symptoms that go unrecognized or misdiagnosed. Additionally, some people might carry the genetic variation but not develop symptoms due to incomplete penetrance – a phenomenon where not everyone with a disease-causing genetic variant actually develops the disease.

The study’s findings have significant implications for healthcare systems and research initiatives. If REDs are indeed more common than previously thought, there may be a need for increased resources for diagnosis, treatment, and support services. The research also highlights the potential for developing more targeted therapies, as a larger patient population could accelerate clinical trials and drug development.

Moreover, the study emphasizes the importance of genetic testing in diagnosis. As REDs can present with a wide range of symptoms, they may be misdiagnosed or remain undetected without specific genetic tests. The researchers suggest that broader use of genetic screening could help identify affected individuals earlier, potentially leading to better management of symptoms and improved outcomes.

While the study provides valuable insights, the researchers caution that more work is needed to fully understand the implications of their findings. Long-term studies tracking individuals with expanded repeats who don’t initially show symptoms could help clarify the true penetrance of these genetic variations and improve risk assessment.

“These results are extremely important,” says Dr. Sarah Tabrizi, Professor of Clinical Neurology at the UCL Queen Square Institute of Neurology and co-author of the paper. “These data will force us as a community of researchers, academics and doctors to evaluate whether these DNA repeats address an unmet diagnostic need in rare neurological diseases, meaning the investigation of repeat expansion disorders deserves much more close attention now.”