[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Genetic disease](https://durgical.com/en/general-pathology/#a-genetic) › Sex chromosome disorders: Klinefelter and Turner

[General pathology](https://durgical.com/en/general-pathology/) · [Genetic disease](https://durgical.com/en/general-pathology/#a-genetic)

# Sex chromosome disorders: Klinefelter and Turner

- Topic

An extra X chromosome in a male (Klinefelter) or a missing one in a female (Turner) mainly affects the gonads, height and puberty.

Updated 2026-11-01

## Key points

- Klinefelter: tall stature, small firm testes, gynaecomastia, azoospermia; low testosterone with high FSH and LH.
- Turner: short stature (SHOX gene), streak ovaries, primary amenorrhoea; low oestrogen with high FSH and LH.
- Turner: bicuspid aortic valve, coarctation of the aorta, horseshoe kidney, webbed neck and lymphoedema of the hands and feet at birth.
- Intelligence is usually normal in Turner; in Klinefelter, language and learning difficulties are common.
- If a Turner patient has Y chromosome material, the risk of gonadoblastoma rises and removal of the gonads is advised.

## What it is

Sex chromosome aneuploidies are tolerated better than autosomal ones because extra X chromosomes are inactivated and the Y carries few genes. Even so, Klinefelter syndrome (47,XXY) is the commonest genetic cause of male hypogonadism and infertility, and Turner syndrome (45,X) is the commonest chromosomal cause of primary amenorrhoea.

## Structure

- Testis in Klinefelter: small, fibrosed, hyalinised seminiferous tubules with few or no germ cells and prominent clusters of Leydig cells.
- Ovary in Turner: a streak of fibrous stroma without follicles, from accelerated loss of oocytes during fetal life.
- The cystic hygroma of the neck in a fetus with Turner (dilated lymphatics) later leaves the webbed neck.

## Step by step

- Early in development, each female cell randomly inactivates one of its two X chromosomes (lyonisation), guided by XIST RNA.
- The inactive X condenses and is seen as a Barr body next to the nuclear membrane.
- Some genes escape inactivation, such as those of the pseudoautosomal region (for example SHOX).
- So a missing X (Turner) leaves a single dose of those genes: short stature and ovarian failure.
- And an extra X (Klinefelter) gives one dose too many: long legs and testicular failure.

## The sex chromosome syndromes

| Syndrome | Karyotype | Gonads and hormones | Body features | Associations |
| --- | --- | --- | --- | --- |
| [Klinefelter syndrome](https://durgical.com/en/conditions/klinefelter-syndrome/) | 47,XXY (mosaics too) | Hyalinised seminiferous tubules; low testosterone, high FSH and LH | Tall, long limbs, gynaecomastia, sparse body hair | Infertility, osteoporosis, higher risk of male breast cancer |
| [Turner syndrome](https://durgical.com/en/conditions/turner-syndrome/) | 45,X; mosaics; isochromosome Xq | Streak ovaries; low oestrogen, high FSH and LH | Short stature, webbed neck, broad chest, low hairline | Bicuspid valve, coarctation, horseshoe kidney, hypothyroidism |
| 47,XYY | An extra Y | Fertility usually normal | Tall | Learning difficulties; many are never diagnosed |
| 47,XXX | An extra X | Fertility usually normal | Tall | Learning and language difficulties |

## Memory aid

Klinefelter: the tall man who cannot father children; Turner: the short girl whose puberty never starts; both with sky-high FSH.

## Test yourself

Think of the answer, then tap the question to see it.

## What hormone profile does a man with Klinefelter syndrome have?

Hypergonadotropic hypogonadism: low testosterone with high FSH and LH because testicular feedback is lost.

## Which cardiovascular defect is commonest in Turner syndrome?

Bicuspid aortic valve; coarctation of the aorta is also characteristic.

## Why are X aneuploidies tolerated better than autosomal ones?

Because every X except one is inactivated; only genes that escape inactivation end up at an abnormal dose.

## Which tumour threatens a Turner patient who carries Y chromosome material?

Gonadoblastoma of the dysgenetic gonad, which is why its removal is recommended.

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## Related

- [Chromosome abnormalities: number and structure](https://durgical.com/en/general-pathology/chromosome-abnormalities-number-and-structure/)
- [Trisomies 21, 18 and 13, and the 22q11.2 deletion](https://durgical.com/en/general-pathology/trisomies-21-18-and-13-and-the-22q11-2-deletion/)
- [Fetal hydrops: immune and nonimmune](https://durgical.com/en/general-pathology/fetal-hydrops-immune-and-nonimmune/)

## Related conditions

- [Klinefelter syndrome (47,XXY)](https://durgical.com/en/conditions/klinefelter-syndrome/)
- [Turner syndrome](https://durgical.com/en/conditions/turner-syndrome/)
- [Male hypogonadism](https://durgical.com/en/conditions/male-hypogonadism/)
- [Male infertility](https://durgical.com/en/conditions/male-infertility/)
- [Primary ovarian insufficiency](https://durgical.com/en/conditions/primary-ovarian-insufficiency/)
- [Coarctation of the aorta](https://durgical.com/en/conditions/coarctation-of-the-aorta/)
- [Congenital kidney anomalies (horseshoe kidney, renal agenesis)](https://durgical.com/en/conditions/congenital-kidney-anomalies/)
- [Hypothyroidism](https://durgical.com/en/conditions/hypothyroidism/)
- [Breast cancer](https://durgical.com/en/conditions/breast-cancer/)

## Elsewhere in DurgiPedia

- [Sex determination: SRY, anti-Müllerian hormone and testosterone](https://durgical.com/en/embryology/sex-determination-sry-anti-mullerian-hormone-and-testosterone/)
- [Differences of sex development: CAH, AIS and 5α-reductase](https://durgical.com/en/embryology/differences-of-sex-development-cah-ais-and-5-reductase/)
- [Meiosis and nondisjunction: where trisomies come from](https://durgical.com/en/embryology/meiosis-and-nondisjunction-where-trisomies-come-from/)
- [Puberty](https://durgical.com/en/physiology/puberty/)
- [Epigenetics: DNA and histone methylation](https://durgical.com/en/biochemistry/topics/epigenetics-dna-and-histone-methylation/)

[← All of general pathology](https://durgical.com/en/general-pathology/)

Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Klinefelter syndrome: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/klinefelter-syndrome/) (MedlinePlus, US National Library of Medicine, 2026); [Turner syndrome: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/turner-syndrome/) (MedlinePlus, US National Library of Medicine, 2026); [Can changes in the number of chromosomes affect health and development?: MedlinePlus Genetics](https://medlineplus.gov/genetics/understanding/mutationsanddisorders/chromosomalconditions/) (MedlinePlus, US National Library of Medicine, 2026).

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Source: https://durgical.com/en/general-pathology/sex-chromosome-disorders-klinefelter-and-turner/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/sex-chromosome-disorders-klinefelter-and-turner/