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Swyer syndrome 46XY gonadal dysgenesis summary
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Here is a concise summary of Swyer Syndrome (also called 46,XY Complete Gonadal Dysgenesis):
Swyer Syndrome - Summary
Definition
A disorder of sex development (DSD) where an individual has a 46,XY karyotype (genetically male) but develops a female phenotype due to complete failure of gonadal development.
Cause / Pathophysiology
- Caused by a mutation or deletion of the SRY gene (sex-determining region on the Y chromosome short arm)
- Normally, SRY encodes testis-determining factor (TDF), which triggers a cascade activating:
- SOX9 gene → produces AMH (anti-Mullerian hormone)
- SF-1 gene → steroidogenesis
- In Swyer syndrome, this cascade fails entirely - gonads remain as non-functional streak gonads
- Because there is no testosterone or AMH production:
- Female external genitalia develop (default pathway)
- Mullerian structures persist (uterus, fallopian tubes, vagina are present)
- No ovaries or testes are present
Clinical Features
| Feature | Detail |
|---|---|
| Karyotype | 46,XY |
| External genitalia | Normal female |
| Internal structures | Uterus + fallopian tubes present; no ovaries |
| Gonads | Streak gonads (non-functional fibrous tissue) |
| Puberty | Primary amenorrhea; no secondary sexual characteristics |
| Stature | Normal to tall female |
| Hormone levels | Low estrogen, elevated FSH and LH |
Diagnosis
- Suspected at puberty when primary amenorrhea + absent breast development occurs
- Confirmed by karyotype (46,XY)
- Hormone profile: elevated gonadotropins (FSH, LH), low sex steroids
- Pelvic ultrasound/MRI: shows streak gonads, intact uterus
Key Complication - Gonadal Malignancy
- Streak gonads carry a 20-30% risk of gonadal tumors, most commonly:
- Dysgerminoma (most common)
- Gonadoblastoma
- Gonadectomy is recommended promptly after diagnosis
Treatment
- Bilateral gonadectomy - to remove malignancy risk
- Hormone replacement therapy (HRT) - estrogen (+/- progesterone) to:
- Induce puberty (breast development, uterine growth)
- Maintain bone density
- Fertility - pregnancy is possible via donor egg IVF (uterus is functional)
- Psychological support and counseling
Memory Hook
Swyer = SRY fails → No testes formed → No testosterone/AMH → Female phenotype with XY karyotype → Streak gonads → Cancer risk → Gonadectomy needed
Sources: Histology: A Text and Atlas (Histology textbook, p.2080); StatPearls - Gonadal Dysgenesis; Smith & Tanagho's General Urology, 19th Ed.
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