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Evolution and natural selection
Independent assortment of genes and linkage
Mendelian genetics and punnett squares
Alagille syndrome (NORD)
Familial adenomatous polyposis
Multiple endocrine neoplasia
Polycystic kidney disease
Treacher Collins syndrome
von Hippel-Lindau disease
Gaucher disease (NORD)
Glycogen storage disease type I
Glycogen storage disease type II (NORD)
Glycogen storage disease type III
Glycogen storage disease type IV
Glycogen storage disease type V
Mucopolysaccharide storage disease type 1 (Hurler syndrome) (NORD)
Niemann-Pick disease type C
Niemann-Pick disease types A and B (NORD)
Primary ciliary dyskinesia
Sickle cell disease (NORD)
Tay-Sachs disease (NORD)
Cri du chat syndrome
Fragile X syndrome
Down syndrome (Trisomy 21)
Edwards syndrome (Trisomy 18)
Patau syndrome (Trisomy 13)
Fabry disease (NORD)
Glucose-6-phosphate dehydrogenase (G6PD) deficiency
Mucopolysaccharide storage disease type 2 (Hunter syndrome) (NORD)
Ornithine transcarbamylase deficiency
Autosomal trisomies: Pathology review
Miscellaneous genetic disorders: Pathology review
Muscular dystrophies and mitochondrial myopathies: Pathology review
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Living with Klinefelter Syndrome
Testicular Disorders & Cancer
Klinefelter syndrome p. 657
chromosome association p. 62
gynecomastia p. 669
testicular tumors p. 672
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.
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