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Androgen Insensitivity Syndrome (AIS) — formerly testicular feminization syndrome — is a genetic condition causing resistance to androgens (male hormones) in individuals with a 46,XY karyotype (genetically male).
Caused by mutations in the androgen receptor (AR) gene on the X chromosome.
Despite having male (XY) chromosomes and testes, their bodies partially or completely do not respond to androgens, leading to varying degrees of undervirilization.
❌ Genetic females (46,XX)
Cannot be affected — they do not carry a Y chromosome and do not rely on androgen receptors for typical female development.
Leads to impaired virilization despite normal or elevated androgen levels.
Classified into three forms:
| Type | External Genitalia | Key Features | Typical Presentation |
|---|---|---|---|
| CAIS (Complete) | Female | No uterus, undescended testes, short vagina, breast dev., ↓ pubic/axillary hair | Primary amenorrhea (teen), inguinal hernia (child) |
| PAIS (Partial) | Ambiguous (♀↔♂) | Genital ambiguity (e.g., micropenis, clitoromegaly), gynecomastia, infertility | At birth (ambiguous genitalia) or puberty |
| MAIS (Mild) | Male | Normal male genitals, gynecomastia, ↓ body hair, infertility | Late – infertility or gynecomastia |
AIS Subtypes:
Complete AIS (CAIS):
Individuals appear female but are genetically male (46,XY). There's complete resistance to androgens.
Partial AIS (PAIS):
A spectrum of ambiguous genitalia due to partial androgen...
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