Diagnostic Criteria and Clinical Features of Androgen Insensitivity Syndrome, Müllerian Agenesis, and Turner Syndrome

Introduction to Diagnostic Criteria

The American College of Medical Genetics recommends karyotype analysis as the definitive test to differentiate Androgen Insensitivity Syndrome, Müllerian agenesis, and Turner syndrome in patients presenting with primary amenorrhea 1

Complete Androgen Insensitivity Syndrome (CAIS) presents with 46,XY karyotype, Müllerian agenesis with 46,XX karyotype, and Turner syndrome with 45,X or mosaic variants, according to the American College of Medical Genetics 1, 2
Müllerian agenesis (MRKH) is characterized by a 46,XX karyotype with normal ovarian function but congenital absence of Müllerian structures, as stated by the American Society for Reproductive Medicine 1
Turner syndrome results from complete or partial loss of the second X chromosome, leading to 45,X (monosomy) or mosaic karyotypes (e.g., 45,X/46,XX), according to the Endocrine Society 3

CAIS patients present with female external genitalia, absent uterus and fallopian tubes, intra-abdominal or inguinal testes, and characteristically sparse or absent pubic/axillary hair, as described by the European Society for Paediatric Endocrinology 4, 1
Müllerian agenesis presents with normal female external genitalia, normal breast development, normal pubic/axillary hair, but congenital absence of the uterus and upper vagina, according to the American College of Obstetricians and Gynecologists 1
Turner syndrome presents with short stature, ovarian dysgenesis with hypergonadotropic hypogonadism, cardiovascular malformations, and characteristic dysmorphic features, as stated by the European Society of Human Genetics 2, 3

The American College of Medical Genetics recommends hormonal assessment, including measurement of FSH, LH, testosterone, and estradiol, to differentiate between CAIS, Müllerian agenesis, and Turner syndrome 1
Karyotype analysis is essential to definitively distinguish between the three conditions, according to the American Society of Human Genetics 1
Imaging evaluation, such as pelvic ultrasound or MRI, is necessary to assess Müllerian structures and gonads, as recommended by the Society of Radiologists in Ultrasound 1

Bicornuate uterus results from incomplete fusion of the Müllerian ducts, characterized by a single cervix with varying degrees of uterine body separation, according to the American Society for Reproductive Medicine 5
Didelphic uterus (Uterus Didelphys) results from complete failure of Müllerian duct fusion, characterized by two separate uterine bodies and two cervices, as described by the European Society of Human Reproduction and Embryology 5

The Endocrine Society warns against confusing CAIS with Müllerian agenesis, as both present with primary amenorrhea and absent uterus, but karyotype, testosterone levels, and presence/absence of pubic hair definitively distinguish them 1
The American Heart Association recommends using indexed aortic measurements (ASI) rather than absolute dimensions to assess aortic dilation in Turner syndrome, as small body size can mask significant aortic dilation 2, 3
The American College of Cardiology recommends baseline cardiac MRI at Turner syndrome diagnosis, as echocardiography alone misses important structural abnormalities 2, 3

CAIS is caused by mutations in the androgen‑receptor (AR) gene that abolish receptor activity, so target tissues are completely insensitive to androgens despite normal‑to‑elevated male‑range testosterone levels. 6
Severe defects in the AR prevent masculinization of XY fetuses, resulting in an unambiguous female external phenotype even though circulating testosterone is in the male range. 6

The classic triad includes female external genitalia with normal breast development, which results from increased peripheral conversion of testosterone to estrogen at puberty. 6

Gonadectomy is recommended because the risk of gonadal malignancy in CAIS ranges from approximately 3 % to 50 %; surgery is typically performed after spontaneous puberty completion. [6][7]
After gonadectomy, lifelong estrogen replacement therapy is advised to preserve bone health and prevent menopausal‑type symptoms. [6][7]
Individuals with CAIS develop a feminine gender identity and sexual orientation, reflecting brain insensitivity to androgens combined with a female social upbringing. [6][7]