Many Rare Diseases Affect Women and Men Differently

Rare Disease Day is observed on the last day of February to raise awareness and drive change for the estimated 300 million people currently living with a rare disease globally (about 4 percent of the world's population). While significant progress has been made over the last two decades in research and availability of medicines, treatment remains challenging due to clinical heterogeneity, limited research and costs. The distribution and prevalence of specific rare diseases can vary significantly across different regions and populations.

A study published last year in The Lancet highlights, for example, the sizeable differences in the share of female and male patients across some of the most prevalent rare diseases, underscoring how unevenly these conditions can affect women and men. Understanding who is most affected and why can be crucial, not only for diagnosis and awareness, but also for targeting research, healthcare resources and support where they're needed most.

As our chart shows, interstitial cystitis is overwhelmingly reported among women, who account for 88.3 percent of patients. Several other conditions also skew female, including polymyalgia rheumatica (69.4 percent) and trigeminal neuralgia (68.1 percent), the former standing out for its comparatively high prevalence of 2,832 per million, the highest among the rare diseases displayed.

Other rare diseases are far closer to parity. Huntington's disease is split more evenly (53.4 percent female vs. 46.6 percent male), while interatrial communication (a congenital cardiac defect) is almost perfectly balanced (50.5 percent vs. 49.5 percent). At the other end of the spectrum, haemophilia remains significantly more prevalent in the male population, with men representing 60.6 percent of haemophilia A cases and 62.7 percent of haemophilia B.

Part of this gap reflects biology. Some rare diseases are directly linked to sex chromosomes: haemophilia, for example, is typically X‑linked, meaning mutations on the X chromosome are more likely to cause disease in males (who have only one X). Beyond genetics, differences in hormones and immune function can also influence susceptibility and symptom profiles. For instance, autoimmune and inflammatory diseases often show female predominance.