G9. Chromosomal Abnormalities: Turner Syndrome, Klinefelter Syndrome

I. Kallmann Syndrome

Pathomechanism

1. Failed migration of GnRH-secreting neurons and olfactory neurons.
2. Decreased GnRH synthesis in hypothalamus → decreased FSH/LH → decreased estrogen.
3. Result: hypogonadotropic hypogonadism → no/poor secondary sex characteristics + failure of ovarian maturation.

Clinical Features

• Anosmia or hyposmia: absent/reduced smell sensation.
• Primary amenorrhea and delayed puberty.
• Infertility due to absent gonadotropin stimulation.
• External genitalia: normal female external genitalia.
• Internal genitalia: uterus and vagina present because Mullerian development is normal.

Diagnosis and Treatment

• Diagnosis: amenorrhea + delayed puberty + anosmia/hyposmia.
• Karyotype: usually normal 46,XX in female patients.
• Labs: decreased GnRH effect, decreased FSH/LH, decreased estrogen.
• MRI: absent/hypoplastic olfactory bulbs may be seen; also exclude hypothalamic-pituitary lesion.
• Treatment: estrogen replacement → later cyclic estrogen + progestin → induction/maintenance of secondary sex characteristics and uterine protection.
• Fertility treatment: pulsatile GnRH or gonadotropins → ovulation induction.

II. Turner Syndrome

Definition and Pathomechanism

• Turner syndrome: complete or partial monosomy X, classically 45,X.
• Cause: sex chromosome loss due to meiotic/mitotic nondisjunction or mosaicism.
• Gonads: ovarian dysgenesis / streak ovaries → low estrogen.
• Hormonal pattern: low estrogen → no negative feedback → increased FSH/LH = hypergonadotropic hypogonadism.
• Development: female external genitalia; uterus present but often small/hypoplastic without estrogen exposure.
• High-yield role: important cause of primary amenorrhea.

Clinical Features

• Primary amenorrhea, delayed/absent puberty, poor secondary sex characteristics.
• Streak ovaries: nonfunctional fibrous gonadal tissue → infertility.
• Short stature.
• Shield chest with widely spaced nipples.
• Webbed neck, cystic hygroma, neonatal lymphedema of hands/feet.
• Cubitus valgus.
• Cardiac: bicuspid aortic valve, coarctation of aorta, aortic root disease, hypertension.
• Renal: horseshoe kidney and other renal anomalies.
• Metabolic: glucose intolerance, obesity risk.

Diagnosis

• Karyotype: 45,X or mosaic/structural X abnormality.
• Labs: increased FSH/LH, decreased estrogen.
• Pelvic ultrasound: streak ovaries, small uterus.
• Echocardiography/cardiac MRI: assess coarctation, bicuspid valve and aortic root risk.
• Renal imaging: screen for renal malformations.
• Screen associated disease: thyroid disease, metabolic risk, hearing problems, hypertension.

Treatment

• Growth hormone in childhood → improve adult height.
• Estrogen therapy → induction of puberty and secondary sex characteristics.
• Later cyclic estrogen + progestin → maintain uterus/endometrium and bone health.
• Fertility: spontaneous pregnancy rare, more possible in mosaic cases; donor-oocyte IVF may be possible after strict cardiac risk assessment.
• Pregnancy risk: aortic dissection risk → cardiology assessment is essential before pregnancy.
• Gonadectomy: indicated if Y-chromosome material is present because of gonadoblastoma risk; not routine for classic 45,X without Y material.

III. Klinefelter Syndrome

Definition and Pathomechanism

• Klinefelter syndrome: male sex chromosome aneuploidy, classically 47,XXY.
• Cause: maternal or paternal meiotic nondisjunction; risk slightly increases with advanced maternal age.
• Testes: seminiferous tubule dysgenesis + testicular atrophy.
• Hormonal pattern: decreased testosterone with increased LH/FSH = hypergonadotropic hypogonadism.
• Estrogen effect relatively increased → gynecomastia.
• Barr body: present because of inactivated extra X chromosome.

Clinical Features

• Male phenotype, often diagnosed for infertility or delayed/abnormal puberty.
• Small firm testes, testicular atrophy.
• Infertility, usually azoospermia or severe oligospermia.
• Hypogonadism: reduced libido, erectile dysfunction, reduced muscle mass.
• Gynecomastia, especially in adolescence.
• Reduced facial/body hair.
• Tall stature, long extremities, eunuchoid body habitus.
• Osteopenia/osteoporosis in adulthood.
• Learning, language or psychosocial difficulties may occur; intelligence is often normal or mildly affected.

Diagnosis and Treatment

• Karyotype: 47,XXY or mosaic variant.
• Labs: decreased testosterone, increased FSH/LH; estrogen may be relatively increased.
• Testicular ultrasound: small/atrophic testes when needed.
• Semen analysis: azoospermia/severe oligospermia.
• Treatment: testosterone replacement from puberty/adulthood when indicated → virilization, bone protection, muscle mass and wellbeing.
• Fertility: assisted reproduction may be possible, e.g. sperm retrieval + ICSI in selected patients.
• Gynecomastia: observation, medical/surgical management if severe or persistent.

IV. Oral-Exam Comparison

Hormonal Patterns

• Kallmann: low GnRH → low FSH/LH → low estrogen = hypogonadotropic hypogonadism.
• Turner: ovarian failure → high FSH/LH + low estrogen = hypergonadotropic hypogonadism.
• Klinefelter: testicular failure → high FSH/LH + low testosterone = hypergonadotropic hypogonadism.

Fast Differentiation

• Kallmann: anosmia + delayed puberty + normal uterus + low gonadotropins.
• Turner: short stature + streak ovaries + webbed neck/shield chest + 45,X + high gonadotropins.
• Klinefelter: tall male + small testes + gynecomastia + infertility + 47,XXY.