What specific medical conditions are included in the 1.7% intersex estimate and how common is each?
Executive summary
The oft‑quoted 1.7% upper‑bound estimate of people “born with intersex traits” is not a single diagnostic category but a compilation that counts many different sex‑development variations — and most of that percentage is driven by late‑onset congenital adrenal hyperplasia (LOCAH); when scholars narrow the definition to conditions that create ambiguous genitalia or chromosomal/phenotypic discordance, prevalence estimates fall to about 0.018% (one in ~5,500) [1] [2]. Reporting and advocacy use different definitions: population surveys that rely on self‑report produce the 1.7% figure [3], while clinical critiques and narrower DSD definitions produce much smaller estimates [2] [4].
1. The makeup of the 1.7%: which medical conditions were counted and why
Fausto‑Sterling’s broader compilation and subsequent summaries list a range of variations included in the 1.7% figure: late‑onset congenital adrenal hyperplasia (LOCAH), Klinefelter syndrome (47,XXY), Turner syndrome (45,X), sex chromosome variants 47,XYY and 47,XXX, vaginal agenesis, androgen insensitivity syndromes, and other rarer conditions such as ovotestes and mixed gonadal dysgenesis; many of these were listed in academic summaries and encyclopedia entries discussing the 1.7% estimate [1] [5].
2. How common is each major condition — the headline numbers
Several sources provide specific prevalence estimates: LOCAH is the dominant contributor, estimated at roughly 1 in 66 people (about 1.5 percentage points of the population) and hence explains most of the 1.7% figure [1] [5]. Klinefelter syndrome (47,XXY) is about 1 in 1,000 births (0.1%) [5]. Classic congenital adrenal hyperplasia (the salt‑wasting/classical form) shows up around 1 in 13,000 births (≈0.0077%) while androgen insensitivity syndrome (complete AIS) is also cited near 1 in 13,000 [5]. Partial AIS was estimated far rarer at about 1 in 130,000 [5]. Vaginal agenesis appears around 1 in 6,000 births [5]. Ovotesticular DSD figures as rare — roughly 1 in 83,000 [5]. Other anomalies and idiopathic presentations are listed in the medical literature at frequencies down to 1 in 110,000 or with no good estimate provided [5].
3. Why the totals diverge: LOCAH’s outsized effect and definitional choices
The reason the 1.7% number can look so large is that LOCAH alone accounts for about 1.5 percentage points; add more common but often phenotypically typical chromosomal variants (like Klinefelter and Turner) and you approach 1.7% [1] [5]. Critics argue that including conditions where chromosomal sex aligns with an unambiguous male or female phenotype — for example mosaic 47,XXX or 47,XYY without external ambiguity — expands “intersex” beyond clinical norms and inflates prevalence [2] [4]. Scholars and clinicians who insist on a narrower definition — ambiguous genitalia or true discordance between chromosomal and phenotypic sex — calculate a prevalence near 0.018% [2] [6].
4. Conflicting sources and the role of self‑report versus clinical diagnosis
Survey‑based research that asks people if they were “born intersex” or with variations yields the 1.7% self‑report rate in some large LGBT‑focused samples, but those data do not medically verify diagnoses and likely include people who interpret “intersex” broadly or mistakenly [3]. Human‑rights organizations and advocacy groups often retain the 1.7% upper bound to capture the wider population of people who risk stigmatization because of sex variations [7] [8] [9], while clinicians and geneticists point to much smaller figures when limiting the definition to DSDs diagnosable at birth or tied to ambiguous genitalia [2] [6].
5. What the reporting leaves unresolved and why precision matters
Available sources concur that definitions drive prevalence: counting LOCAH and common chromosomal variants yields ~1.7%, excluding them yields ~0.018%, and intermediate figures (0.05% to 0.5%) appear when focusing on clinically identifiable ambiguous genitalia or “severe” DSDs [1] [2] [6]. The literature provided does not supply a single, authoritative breakdown that adds every condition’s precise fractional contribution to the 1.7% composite beyond the LOCAH and Klinefelter examples; that gap is why public debate often pits clinical narrowness against advocacy inclusiveness [3] [1].