Elite Female Athletes Show Unexpectedly High Rates of XY Chromosomal Variants
A large LCMS study of 1,689 elite track and field athletes reveals XY DSD prevalence far exceeds general population rates.
Summary
Researchers analyzed serum androgens in nearly 1,700 elite track and field athletes to better understand how rare chromosomal conditions affect hormone profiles in competitive sport. Using highly sensitive mass spectrometry across 19 certified labs, they found that XY Disorders of Sex Development — particularly 5-alpha reductase deficiency — appear far more often among elite female athletes than in the general population. These athletes showed testosterone and DHT levels resembling biological males. The study also validated a testosterone-to-DHT ratio as a practical diagnostic tool for identifying 5-alpha reductase deficiency in athletic populations. The findings have significant implications for sports eligibility policies and the science of sex-based performance advantages.
Detailed Summary
Understanding how biological sex influences athletic performance is one of the most contested areas in sports medicine. At the center of this debate are rare chromosomal conditions known as XY Disorders of Sex Development (DSD), where individuals with male chromosomes may present with female or ambiguous physical characteristics. This study provides the most rigorous hormonal characterization of elite athletes with XY DSD to date.
Researchers from the University of Sydney and World Athletics analyzed serum samples from 1,689 elite track and field athletes — 889 male and 800 female — collecting 5,516 total samples. Using liquid chromatography-mass spectrometry (LCMS) across 19 WADA-accredited laboratories, they measured testosterone, dihydrotestosterone (DHT), and androstenedione. A linear mixed model adjusted for repeated measures was applied to the data.
The results were striking. Male athletes averaged testosterone of 19.7 nmol/L, while female athletes averaged just 1.1 nmol/L. Among female athletes, 14 individuals were identified with XY DSD — 12 with 5-alpha reductase type 2 deficiency (5ARD) and 2 with androgen insensitivity syndrome (AIS). These athletes showed testosterone levels of 28.9 nmol/L and a T/DHT ratio of 32.0, both firmly in the male range. Critically, the prevalence of XY DSD in this elite female cohort vastly exceeds community estimates.
The study also validates the serum T/DHT ratio measured by LCMS as a reliable diagnostic marker for 5ARD — a condition where testosterone is not efficiently converted to the more potent DHT. This ratio could become a standard screening tool in elite sports.
For clinicians and sports governing bodies, these findings underscore the complexity of sex-based eligibility rules. The overrepresentation of androgen-sensitive XY DSD athletes in elite competition raises important questions about competitive fairness and the need for nuanced, evidence-based policies.
Key Findings
- XY DSD prevalence among elite female athletes far exceeds general population estimates.
- 5-alpha reductase deficiency (5ARD) was the most common XY DSD identified, with 12 cases.
- XY DSD athletes showed testosterone levels (~28.9 nmol/L) comparable to male athletes.
- Serum T/DHT ratio by LCMS reliably identifies 5ARD and can be applied in elite sport screening.
- Male athletes averaged 19.7 nmol/L testosterone versus 1.1 nmol/L in female athletes.
Methodology
Cross-sectional analysis of 5,516 serum samples from 1,689 elite track and field athletes using LCMS across 19 WADA-accredited laboratories. A linear mixed model for repeated measures was used, with adjustments for multiple comparisons and imputation for left-censored DHT data. Pregnancy and doping samples were excluded from primary analyses.
Study Limitations
The summary is based on the abstract only, as the full text is not open access. The study is observational and cross-sectional, limiting causal inference. Clinical diagnoses of DSD subtypes relied on existing records and may not capture all cases uniformly.
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