Background

Fragile X syndrome (FXS) is a genetic condition, often causing intellectual disability, developmental delays, and other health or behavioural challenges. The number of people who are diagnosed with FXS is known, but many individuals with FXS may be undiagnosed. Knowing both the diagnosed and undiagnosed numbers is important for planning health and support services, and for understanding the true burden of the condition in the population.

Study Methods

• We used retrospective data from UK health records to count how many people have a recorded diagnosis of FXS.
• This was combined with statistical modelling to estimate how many people likely have FXS but remain undiagnosed, based on known rates from genetic screening studies and demographics.
• We also examined how these numbers vary by age and sex
• Supplementary data (such as medical codes/diagnostic codes) were used to validate and refine these estimates.

Key Findings

• The diagnosed prevalence of FXS in the UK is lower than what screening studies suggest. In other words, many cases are likely going undetected.
• The model estimates that for every person with a recorded diagnosis, there may be several more who are undiagnosed.
• The gap between diagnosed and estimated total cases was particularly large among adults and in women, implying under-recognition in older age groups.
• FXS is more common than was previously thought, potentially affecting up to 1 in 2500 men and 1 in 6250 women in the UK

Conclusion

This study suggests that a substantial number of people in the UK who have fragile X syndrome are not being diagnosed. The under-diagnosis is especially marked in adults, and varies by location. To better serve individuals with FXS and their families, there is a need for expanded genetic screening, improved awareness among healthcare providers, and more equitable access to diagnostic services.