Revisiting the SRY Test in female athlete eligibility

New SRY-gene screenings by World Athletics for female athlete eligibility reopens a sensitive debate overlapping genetics, endocrinology, and ethics.

The SRY gene test to define the female category in sports

In September 2025, World Athletics introduced a regulation requiring athletes competing in the women’s category to undergo genetic testing for the presence of the SRY gene. Intended as an objective marker of biological sex, this approach has provoked widespread discussion among clinicians, ethicists, and sports professionals. At issue is not only whether SRY accurately reflects biological sex, but also whether it is appropriate to use a single molecular determinant in contexts where fairness, privacy, and human rights are equally at stake.

Biology of sex determination

The discovery of the Sex-determining Region Y (SRY) gene on the Y chromosome in 1990 marked a turning point in human genetics. Sinclair and colleagues demonstrated that SRY encoded a transcription factor capable of directing the bipotential gonad towards testis development. Shortly thereafter, functional evidence in murine models confirmed that insertion of SRY into XX embryos was sufficient to induce testicular differentiation. SRY activates downstream targets such as SOX9, which further promotes Sertoli cell differentiation and the production of anti-Müllerian hormone, setting in motion a cascade that leads to the regression of Müllerian ducts and masculinization of the embryo.

Yet, SRY alone is not always sufficient. Mutations or deletions in the gene can result in 46,XY gonadal dysgenesis (Swyer syndrome), in which individuals present with a female phenotype despite the presence of a Y chromosome. Conversely, translocation of SRY onto the X chromosome may cause testicular development in 46,XX individuals. These observations underscore that sex determination is not dictated by a single genetic switch but by a network of genes and hormonal signals.

Differences of Sex Development (DSD)

Disorders or differences of sex development represent a heterogeneous group of conditions in which chromosomal, gonadal, or phenotypic sex diverge from the typical binary. Complete androgen insensitivity syndrome (CAIS) exemplifies the limitations of an SRY-based approach: individuals with a 46,XY karyotype and intact SRY produce normal levels of testosterone, yet mutations in the androgen receptor render tissues unresponsive, leading to a fully female phenotype. Similarly, 5-alpha-reductase deficiency prevents the conversion of testosterone into dihydrotestosterone, resulting in undervirilisation at birth but variable virilization at puberty.

The prevalence of DSD is estimated at approximately 1 in 4,500 live births, though definitions vary. While rare, these conditions become particularly visible in elite sport, where physiological outliers are scrutinized. The World Athletics regulations of recent years, initially centred on testosterone levels, have already faced criticism for disproportionately targeting athletes with DSD, raising concerns about medical ethics and human rights.

The limitations of SRY as a criterion

The reliance on SRY status as a binary gatekeeper for female athlete eligibility is scientifically problematic. The presence of SRY does not equate to male phenotypic development, as demonstrated in CAIS and other DSD conditions. Conversely, its absence does not guarantee female phenotype, as in cases of XX males due to SRY translocation. From a clinical perspective, the test risks generating results that require genetic counseling, careful communication, and potentially lifelong medical implications, elements that go far beyond the remit of a sports federation.

Furthermore, the association between SRY status and athletic performance remains indirect. While testosterone levels and androgen sensitivity are more directly linked to muscle mass and haemoglobin concentration, SRY itself is upstream and does not guarantee a competitive advantage. The test thus risks conflating genetic presence with functional effect.

Ethical and clinical Implications

Implementing SRY testing in sport raises a series of ethical and clinical challenges. Athletes may receive unexpected diagnoses of DSD, confronting them with sensitive genetic information in a non-medical setting. The absence of structured counseling and follow-up may exacerbate stigma and psychological burden. There is also the broader issue of fairness: targeting women with rare genetic variations risks reinforcing exclusionary practices, while ignoring the multifactorial determinants of performance that include training, environment, and socioeconomic context.

For clinicians, the regulation poses new responsibilities. Sports physicians and endocrinologists may be asked to interpret SRY results, manage incidental findings, and support athletes through complex medical and psychological consequences. This reinforces the need for multidisciplinary teams (including geneticists, ethicists, and psychologists) whenever such testing is proposed.

Biology is complex

The introduction of mandatory SRY testing in female athletics highlights the tension between regulatory clarity and biological complexity. While the gene is a critical determinant in sex development, it is neither necessary nor sufficient to define biological sex in all cases, and it bears little direct relation to athletic capacity. For medicine and sport alike, the challenge lies in acknowledging the continuum of human biology without reducing it to a simplistic marker. Future policies should adopt a multidimensional framework, combining chromosomal, hormonal, phenotypic, and ethical perspectives, rather than relying on a single gene to adjudicate eligibility.

Sources and Further Reading
  1. Sinclair AH, Berta P, Palmer MS, Hawkins JR, Griffiths BL, Smith MJ, et al. A gene from the human sex-determining region encodes a protein with homology to a conserved DNA-binding motif. Nature. 1990;346(6281):240-4. PMID: 1695712.
  2. Koopman P, Gubbay J, Vivian N, Goodfellow P, Lovell-Badge R. Male development of chromosomally female mice transgenic for Sry. Nature. 1991;351(6322):117-21. PMID: 2030730.
  3. Hughes IA, Houk C, Ahmed SF, Lee PA; LWPES/ESPE Consensus Group. Consensus statement on management of intersex disorders. Arch Dis Child. 2006;91(7):554-63. PMID: 16624884.
  4. Bashamboo A, McElreavey K. Mechanisms of sex determination in humans: insights from disorders of sex development. Nat Rev Endocrinol. 2016;12(10):595-607. PMID: 27573724.
  5. Bermon S, Garnier PY. Serum androgen levels and their relation to performance in track and field: mass spectrometry results from 2127 observations in male and female elite athletes. Br J Sports Med. 2017;51(17):1309-14. PMID: 28698219.
  6. Harper J, Martínez-Patiño MJ, Pigozzi F, Pitsiladis Y. Implications of a third gender category for elite sports. Br J Sports Med. 2018;52(11):659-60. PMID: 29514853.
  7. Bowman-Smart H, Kelly B, McMillan J. World Athletics regulations unfairly affect female athletes with DSDs. J Med Ethics. 2020;46(9):593-7. PMID: 32699050.
  8. World Athletics. Recommendations to the eligibility conditions for the Female Category. World Athletics; 2025.