Klinefelter syndrome

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Klinefelter syndrome

Genetics

Genetic disorders

Achondroplasia
Alagille syndrome (NORD)
Familial adenomatous polyposis
Familial hypercholesterolemia
Hereditary spherocytosis
Huntington disease
Li-Fraumeni syndrome
Marfan syndrome
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Myotonic dystrophy
Neurofibromatosis
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Treacher Collins syndrome
Tuberous sclerosis
von Hippel-Lindau disease
Albinism
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Cystic fibrosis
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Glycogen storage disease type I
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Niemann-Pick disease type C
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Tay-Sachs disease (NORD)
Wilson disease
Cri du chat syndrome
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Angelman syndrome
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Klinefelter syndrome
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Fragile X syndrome
Friedreich ataxia
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Myotonic dystrophy
Down syndrome (Trisomy 21)
Edwards syndrome (Trisomy 18)
Patau syndrome (Trisomy 13)
Alport syndrome
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Fabry disease (NORD)
Glucose-6-phosphate dehydrogenase (G6PD) deficiency
Hemophilia
Lesch-Nyhan syndrome
Mucopolysaccharide storage disease type 2 (Hunter syndrome) (NORD)
Muscular dystrophy
Ornithine transcarbamylase deficiency
Wiskott-Aldrich syndrome
X-linked agammaglobulinemia
Autosomal trisomies: Pathology review
Miscellaneous genetic disorders: Pathology review
Muscular dystrophies and mitochondrial myopathies: Pathology review

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External References

First Aid

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2021

Estrogen p. 648, 674

Klinefelter syndrome p. 655

Follicle-stimulating hormone (FSH)

Klinefelter syndrome p. 655

Gynecomastia p. 667

Klinefelter syndrome p. 655

Hypogonadism

Klinefelter syndrome p. 655

Infertility

Klinefelter syndrome p. 655

Inhibin

Klinefelter syndrome p. 655

Klinefelter syndrome p. 655

chromosome association p. 62

gynecomastia p. 667

testicular tumors p. 670

Luteinizing hormone (LH)

Klinefelter syndrome p. 655

Testosterone p. 646, 676

Klinefelter syndrome p. 655

Transcript

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Klinefelter syndrome, named after Dr. Harry Klinefelter who first identified it, is a chromosomal problem where a person with an XY genotype - biologically a male - inherits at least one extra X-chromosome, and sometimes a few extra ones.

Having an extra X chromosome makes the testicular cells generate less testosterone, which is the hormone responsible for primary sex characteristics like development of the sex organs as well as secondary sex characteristics like height and body shape.

It’s worth mentioning up front, that we’re using the term male here, rather than boy or man, to talk about the biological category of a person’s sex rather than a person’s gender identity.

Now, in puberty, in both males and females, the hypothalamus starts to release more gonadotropin releasing hormone, which gets the pituitary gland to release luteinizing hormone and follicle-stimulating hormone.

In males, these hormones affect the Leydig cells and the Sertoli cells.

The Leydig cells are in the interstitium of the testes, and in response to luteinizing hormone they convert cholesterol into testosterone.

The testosterone along with follicle-stimulating hormone, then stimulate Sertoli cells in the seminiferous tubules of the testes to make more sperm.

To main balance or homeostasis, testosterone reduces gonadotropin releasing hormone and luteinizing hormone, and Sertoli cells release the hormone inhibin which inhibits release of follicle-stimulating hormone.

In Klinefelter syndrome, this hormone balance is altered.

The extra X-chromosome interrupts the normal function of the Sertoli and Leydig cells.

Starting at puberty and continuing throughout life, Sertoli and Leydig cells don’t produce inhibin or testosterone, respectively.

This means that levels of luteinizing hormone and follicle stimulating hormone increase.

Less testosterone also suppresses testes maturation and sperm production as well as development of secondary male characteristics.

In fact, each additional X-chromosome increases the estrogen to testosterone ratio, making the changes even more striking.

Klinefelter syndrome develops when a gamete, either a sperm or an egg, contains at least one extra X-chromosome.

Typically, a gamete with 23 chromosomes, including one sex chromosome either X or Y, develops when parent germ cells undergo the process of meiosis.

Early on in meiosis the germ cell makes a copy of all of its chromosomes, with each chromosome having sister chromatids at that point.