Sweyer syndrome
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Swyer syndrome 46 XY pure gonadal dysgenesis
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Swyer syndrome clinical features diagnosis management
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46 XY gonadal dysgenesis gonadoblastoma hormone replacement streak gonads
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Swyer Syndrome (46,XY Complete Gonadal Dysgenesis)
Swyer syndrome, formally called complete gonadal dysgenesis (CGD), is a disorder of sex development (DSD) in which an individual carries a 46,XY karyotype but is phenotypically female due to total failure of gonadal differentiation.
Pathophysiology
In normal male development, the SRY gene on the Y chromosome triggers the bipotential gonad to develop into testes. In Swyer syndrome, this process fails — resulting in streak gonads (fibrous, non-functional tissue) instead of testes. Because:
- The streak gonads produce no testosterone → no male internal genitalia or virilization
- They produce no AMH/MIS (anti-Müllerian hormone) → Müllerian structures (uterus, fallopian tubes, upper vagina) persist and develop normally
The individual is therefore born with normal female external and internal genitalia, with a functional uterus.
Genetic causes include:
- Mutations in SRY (~15–20% of cases)
- Mutations in DHH, NR5A1 (SF-1), WT1, SOX9, MAP3K1, and others
- Many cases remain genetically unexplained
Clinical Presentation
| Feature | Detail |
|---|---|
| External genitalia | Normal female |
| Internal genitalia | Uterus, fallopian tubes, upper vagina present |
| Gonads | Bilateral streak gonads (intra-abdominal) |
| Pubertal development | Primary amenorrhea, absent breast development, absent pubic/axillary hair |
| Height | Often tall (no estrogen-mediated epiphyseal closure) |
| Karyotype | 46,XY |
| Gender identity | Typically female |
Most patients present in adolescence with delayed or absent puberty and primary amenorrhea.
Diagnosis
- Karyotype: 46,XY in a phenotypic female
- Hormones: Elevated LH and FSH (hypergonadotropic hypogonadism); low estradiol, low testosterone, low AMH/MIS, low inhibin B
- Imaging (pelvic ultrasound/MRI): Uterus present, streak gonads (may be difficult to visualize)
- Differentiation from Turner syndrome: Turner is 45,X (or mosaic), whereas Swyer is 46,XY with normal female phenotype
Management
1. Gonadectomy (urgent)
- The streak gonads carry a high risk of germ cell cancer (GCC) — particularly gonadoblastoma and dysgerminoma — estimated at 15–35% lifetime risk
- Bilateral gonadectomy is recommended as soon as the diagnosis is confirmed, regardless of age
- Harrison's (p. 10932): "The risk of GCC is high, and intraabdominal gonads should be removed."
2. Hormone Replacement Therapy (HRT)
- Exogenous estrogen is initiated to induce puberty (breast development, uterine growth, bone mineralization)
- Progesterone is added once breakthrough bleeding or adequate uterine development is established
- Lifelong HRT is typically continued until the age of natural menopause
3. Fertility
- Patients cannot produce eggs (no functional ovarian tissue)
- However, they have a uterus, making gestational surrogacy with donor oocytes possible — pregnancies have been successfully achieved
4. Psychological support
- Disclosure and counseling regarding the 46,XY karyotype and infertility are important, ideally through a multidisciplinary DSD team
Key Distinctions
| Swyer Syndrome | Turner Syndrome | CAIS | |
|---|---|---|---|
| Karyotype | 46,XY | 45,X (or mosaic) | 46,XY |
| Gonads | Streak | Streak/dysgenetic | Testes (intra-abdominal) |
| Uterus | Present | Absent/hypoplastic | Absent |
| Phenotype | Normal female | Short stature, webbed neck | Normal female |
| Testosterone | Low | Low | High (insensitive) |
Source: Harrison's Principles of Internal Medicine, 21st Edition, p. 10932
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