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Androgen Insensitivity Syndrome (AIS) is a 46,XY Disorders of sexual development (DSD) characterized by end-organ resistance to androgens due to mutations in the androgen receptor (AR) gene.
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https://www.youtube.com/watch?v=L9zVlkpbU-w
Individuals have male (XY) karyotype, testes, and normal or elevated testosterone, but female external genitalia with absent or underdeveloped internal male or female reproductive structures depending on severity.
Classification
| Type |
Description |
Phenotype |
| Complete AIS (CAIS) |
Complete androgen resistance |
Female external genitalia, no uterus, undescended testes |
| Partial AIS (PAIS) |
Partial receptor function |
Ambiguous genitalia or undervirilized male |
| Mild AIS (MAIS) |
Minimal receptor defect |
Normal male genitalia; possible infertility or gynecomastia |
Pathophysiology
- AR gene mutation on X chromosome (Xq11–12)
- In AIS:
- Testes develop (due to SRY gene on Y chromosome)
- Müllerian ducts regress (due to Anti-Müllerian Hormone)
- But androgens fail to act, so:
- No Wolffian duct derivatives (vas deferens, seminal vesicles)
- External genitalia remain female or ambiguous
- Phenotypic sex depends on degree of receptor functionality
Clinical Features
Complete AIS (CAIS)
- Phenotypic female with:
- Normal breast development at puberty (estradiol from aromatization of testosterone)
- Primary amenorrhea
- Absent uterus and upper vagina
- Blind vaginal pouch
- No axillary or pubic hair (androgen-dependent)
- Undescended testes (inguinal or intra-abdominal)
- Often diagnosed during:
- Workup for amenorrhea
- Inguinal hernia in childhood
- Infertility or absent menses in adolescence
Partial AIS (PAIS)
- Variable genital ambiguity:
- Microphallus, bifid scrotum
- Hypospadias
- Gynecomastia at puberty
- Possible infertility
- Assigned sex may be male or female depending on phenotype
Investigations