Klinefelter syndrome


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Klinefelter syndrome




Citric acid cycle

Electron transport chain and oxidative phosphorylation


Glycogen metabolism

Pentose phosphate pathway

Physiological changes during exercise

Amino acid metabolism

Nitrogen and urea cycle

Fatty acid synthesis

Fatty acid oxidation

Ketone body metabolism

Cholesterol metabolism

Essential fructosuria

Hereditary fructose intolerance


Pyruvate dehydrogenase deficiency

Glucose-6-phosphate dehydrogenase (G6PD) deficiency

Lactose intolerance

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


Metachromatic leukodystrophy (NORD)

Krabbe disease

Gaucher disease (NORD)

Niemann-Pick disease types A and B (NORD)

Niemann-Pick disease type C

Fabry disease (NORD)

Tay-Sachs disease (NORD)

Mucopolysaccharide storage disease type 1 (Hurler syndrome) (NORD)

Mucopolysaccharide storage disease type 2 (Hunter syndrome) (NORD)


Hartnup disease


Ornithine transcarbamylase deficiency

Phenylketonuria (NORD)

Cystinuria (NORD)


Maple syrup urine disease


Familial hypercholesterolemia



Disorders of carbohydrate metabolism: Pathology review

Disorders of fatty acid metabolism: Pathology review

Dyslipidemias: Pathology review

Glycogen storage disorders: Pathology review

Lysosomal storage disorders: Pathology review

Disorders of amino acid metabolism: Pathology review

Cellular structure and function

Cell membrane

Selective permeability of the cell membrane

Extracellular matrix

Cell-cell junctions

Endocytosis and exocytosis


Resting membrane potential

Nernst equation

Cytoskeleton and intracellular motility

Cell signaling pathways

Adrenoleukodystrophy (NORD)

Zellweger spectrum disorders (NORD)

Primary ciliary dyskinesia

Alport syndrome

Ehlers-Danlos syndrome

Osteogenesis imperfecta

Marfan syndrome

Vitamin C deficiency

Peroxisomal disorders: Pathology review

Nuclear structure

DNA structure

Transcription of DNA

Translation of mRNA

Gene regulation


Amino acids and protein folding

Protein structure and synthesis

Nucleotide metabolism

DNA replication

Lac operon

DNA damage and repair

Cell cycle

Mitosis and meiosis

DNA mutations

Lesch-Nyhan syndrome

Orotic aciduria

Adenosine deaminase deficiency

Xeroderma pigmentosum

Li-Fraumeni syndrome

Bloom syndrome

Fanconi anemia

McCune-Albright syndrome

Acute radiation syndrome

Purine and pyrimidine synthesis and metabolism disorders: Pathology review

Polymerase chain reaction (PCR) and reverse-transcriptase PCR (RT-PCR)

Gel electrophoresis and genetic testing

ELISA (Enzyme-linked immunosorbent assay)


DNA cloning

Fluorescence in situ hybridization

Mendelian genetics and punnett squares

Hardy-Weinberg equilibrium

Inheritance patterns

Independent assortment of genes and linkage

Evolution and natural selection

Down syndrome (Trisomy 21)

Edwards syndrome (Trisomy 18)

Patau syndrome (Trisomy 13)

Fragile X syndrome

Huntington disease

Myotonic dystrophy

Friedreich ataxia

Turner syndrome

Klinefelter syndrome

Prader-Willi syndrome

Angelman syndrome

Beckwith-Wiedemann syndrome

Cri du chat syndrome

Williams syndrome

Alagille syndrome (NORD)


Polycystic kidney disease

Familial adenomatous polyposis

Hereditary spherocytosis

Multiple endocrine neoplasia


Tuberous sclerosis

von Hippel-Lindau disease


Cystic fibrosis


Sickle cell disease (NORD)



Wilson disease

X-linked agammaglobulinemia


Muscular dystrophy

Wiskott-Aldrich syndrome

Mitochondrial myopathy

Autosomal trisomies: Pathology review

Muscular dystrophies and mitochondrial myopathies: Pathology review

Miscellaneous genetic disorders: Pathology review


Klinefelter syndrome


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High Yield Notes

3 pages


Klinefelter syndrome

of complete

External References

First Aid








Estrogen p. 654, 680

Klinefelter syndrome p. 661

Follicle-stimulating hormone (FSH)

Klinefelter syndrome p. 661

Gynecomastia p. 673

Klinefelter syndrome p. 661


Klinefelter syndrome p. 661


Klinefelter syndrome p. 661


Klinefelter syndrome p. 661

Klinefelter syndrome p. 661

chromosome association p. 62

gynecomastia p. 673

testicular tumors p. 676

Luteinizing hormone (LH)

Klinefelter syndrome p. 661

Testosterone p. 652, 682

Klinefelter syndrome p. 661


Content Reviewers

Rishi Desai, MD, MPH


Tanner Marshall, MS

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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