A 20-year-old woman has primary amenorrhoea. She has normal female secondary sexual characteristics, a blind-ending vagina on examination, and no uterus on MRI. Karyotype returns 46,XY. Which diagnosis best explains this presentation and what is the mechanism?

• A Turner syndrome (45,X); ovarian dysgenesis prevents oestrogen production
• B Congenital adrenal hyperplasia (CAH); excess androgens suppress the HPO axis
• C Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome; Müllerian agenesis with normal karyotype
• D Complete androgen insensitivity syndrome (CAIS); absent androgen receptor function prevents virilisation despite normal testosterone levels ✓

Explanation

Complete androgen insensitivity syndrome (CAIS) presents as 46,XY with female external phenotype, normal breast development (due to aromatisation of testosterone to oestradiol), absent/sparse pubic and axillary hair, absent uterus and fallopian tubes (because AMH from testes causes Müllerian regression), and a short blind-ending vagina. The androgen receptor (AR) gene is mutated → testosterone cannot act on target tissues → no male differentiation occurs. MRKH syndrome has 46,XX karyotype with Müllerian agenesis and normal ovaries. Turner syndrome has 45,X. CAH causes virilisation, not feminisation, in 46,XY individuals.

Reference: Shaw's Textbook of Gynaecology, 17th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.