A 16-year-old girl presents with primary amenorrhoea, normal breast development, absent pubic and axillary hair, and a 46,XY karyotype. Serum testosterone is in the high-normal male range. This presentation is consistent with:

• A Turner syndrome (45,X) with normal estrogen production
• B Congenital adrenal hyperplasia with 21-hydroxylase deficiency
• C Müllerian agenesis (MRKH syndrome) with XX karyotype
• D Complete androgen insensitivity syndrome (CAIS) — androgen receptor dysfunction prevents target tissue response to testosterone ✓

Explanation

Complete androgen insensitivity syndrome (CAIS) occurs when a functional androgen receptor is absent. The individual (46,XY) has testes that produce normal male testosterone and AMH (Müllerian inhibiting substance). AMH regresses Müllerian ducts (so no uterus or fallopian tubes), but testosterone cannot act on Wolffian duct tissue or external genitalia due to receptor loss — resulting in a female phenotype. Breast development occurs from peripheral oestrogen (from testosterone aromatization). Pubic/axillary hair is androgen-dependent and absent. Testosterone is in the male range; the phenotype is female.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.