Klinefelter syndrome

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Development of the reproductive system
Anatomy and physiology of the male reproductive system
Anatomy of the male reproductive organs of the pelvis
Anatomy of the male urogenital triangle
Precocious and delayed puberty: Clinical
Delayed puberty
Testicular cancer
Testicular tumors: Pathology review
Menstrual cycle
Gardnerella vaginalis (Bacterial vaginosis)
Pelvic inflammatory disease
Vaginal and vulvar disorders: Pathology review
Human papillomavirus
Breast cancer
Fibrocystic breast changes
Intraductal papilloma
Mastitis
Paget disease of the breast
Cervix and vagina histology
Fallopian tube and uterus histology
Mammary gland histology
Ovary histology
Penis histology
Prostate gland histology
Testis, ductus deferens, and seminal vesicle histology
Amenorrhea
Intrauterine growth restriction
Polyhydramnios
Oligohydramnios
Potter sequence
Urethritis
Ectopic pregnancy
Miscarriage
Gestational trophoblastic disease
Germ cell ovarian tumor
Ovarian cyst
Polycystic ovary syndrome
Sex cord-gonadal stromal tumor
Ovarian torsion
Premature ovarian failure
Surface epithelial-stromal tumor
Chorioamnionitis
Female sexual interest and arousal disorder
Orgasmic dysfunction
Genito-pelvic pain and penetration disorder
Cervical cancer
Endometrial cancer
Endometriosis
Uterine fibroid
Endometritis
Endometrial hyperplasia
Choriocarcinoma
Precocious puberty
5-alpha-reductase deficiency
Kallmann syndrome
Turner syndrome
Klinefelter syndrome
Androgen insensitivity syndrome
Penile cancer
Priapism
Hypospadias and epispadias
Benign prostatic hyperplasia
Prostatitis
Prostate cancer
Erectile dysfunction
Male hypoactive sexual desire disorder
Cryptorchidism
Inguinal hernia
Varicocele
Testicular torsion
Orchitis
Epididymitis
Amenorrhea: Pathology review
Benign breast conditions: Pathology review
Breast cancer: Pathology review
Cervical cancer: Pathology review
Complications during pregnancy: Pathology review
Congenital TORCH infections: Pathology review
Disorders of sex chromosomes: Pathology review
Disorders of sexual development and sex hormones: Pathology review
HIV and AIDS: Pathology review
Ovarian cysts and tumors: Pathology review
Penile conditions: Pathology review
Prostate disorders and cancer: Pathology review
Sexually transmitted infections: Vaginitis and cervicitis: Pathology review
Sexually transmitted infections: Warts and ulcers: Pathology review
Testicular and scrotal conditions: Pathology review
Uterine disorders: Pathology review
Androgens and antiandrogens
Aromatase inhibitors
Estrogens and antiestrogens
Progestins and antiprogestins
Uterine stimulants and relaxants
Adrenergic antagonists: Alpha blockers
PDE5 inhibitors
Estrogen and progesterone
Anatomy and physiology of the female reproductive system
Menopause
Puberty and Tanner staging
Breastfeeding
Oxytocin and prolactin
Testosterone
Pregnancy
Stages of labor
Hypertensive disorders of pregnancy: Clinical
Perinatal infections: Clinical
Antepartum hemorrhage: Clinical
Abnormal uterine bleeding: Clinical
Ovarian cysts, cancer, and other adnexal masses: Clinical
Placenta previa
Preeclampsia & eclampsia
Preterm labor
Postpartum hemorrhage
Postpartum hemorrhage: Clinical
Breast abscess: Clinical sciences
Mastitis: Clinical sciences
Anatomy of the breast
Hyperprolactinemia

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Klinefelter syndrome

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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.