5-alpha-reductase deficiency


00:00 / 00:00



5-alpha-reductase deficiency

Reproductive system

Male and female reproductive system disorders

Precocious puberty

Delayed puberty

Klinefelter syndrome

Turner syndrome

Androgen insensitivity syndrome

5-alpha-reductase deficiency

Kallmann syndrome

Male reproductive system disorders

Hypospadias and epispadias

Bladder exstrophy


Penile cancer


Benign prostatic hyperplasia

Prostate cancer


Inguinal hernia




Testicular torsion

Testicular cancer

Erectile dysfunction

Male hypoactive sexual desire disorder

Female reproductive system disorders


Ovarian cyst

Premature ovarian failure

Polycystic ovary syndrome

Ovarian torsion

Krukenberg tumor

Sex cord-gonadal stromal tumor

Surface epithelial-stromal tumor

Germ cell ovarian tumor

Uterine fibroid



Endometrial hyperplasia

Endometrial cancer


Cervical cancer

Pelvic inflammatory disease


Female sexual interest and arousal disorder

Orgasmic dysfunction

Genito-pelvic pain and penetration disorder


Fibrocystic breast changes

Intraductal papilloma

Phyllodes tumor

Paget disease of the breast

Breast cancer

Hyperemesis gravidarum

Gestational hypertension

Preeclampsia & eclampsia

Gestational diabetes

Cervical incompetence

Placenta previa

Placenta accreta

Placental abruption



Potter sequence

Intrauterine growth restriction

Preterm labor

Postpartum hemorrhage


Congenital toxoplasmosis

Congenital cytomegalovirus (NORD)

Congenital syphilis

Neonatal conjunctivitis

Neonatal herpes simplex

Congenital rubella syndrome

Neonatal sepsis

Neonatal meningitis


Gestational trophoblastic disease

Ectopic pregnancy

Fetal hydantoin syndrome

Fetal alcohol syndrome

Reproductive system pathology review

Disorders of sex chromosomes: Pathology review

Disorders of sexual development and sex hormones: Pathology review

Sexually transmitted infections: Vaginitis and cervicitis: Pathology review

Sexually transmitted infections: Warts and ulcers: Pathology review

HIV and AIDS: Pathology review

Penile conditions: Pathology review

Testicular and scrotal conditions: Pathology review

Prostate disorders and cancer: Pathology review

Testicular tumors: Pathology review

Uterine disorders: Pathology review

Ovarian cysts and tumors: Pathology review

Cervical cancer: Pathology review

Vaginal and vulvar disorders: Pathology review

Benign breast conditions: Pathology review

Breast cancer: Pathology review

Complications during pregnancy: Pathology review

Congenital TORCH infections: Pathology review


5-alpha-reductase deficiency


0 / 9 complete

USMLE® Step 1 questions

0 / 1 complete

High Yield Notes

9 pages


5-alpha-reductase deficiency

of complete


USMLE® Step 1 style questions USMLE

of complete

A 15-year-old boy presents to his family physician for a routine school physical. The patient appears anxious and uneasy during the encounter. During the physical exam, the patient confesses that he feels insecure about his body. During gym practice, the patient has noticed that his genitalia appears different from his peers. There is no history of a disorder of sexual development within the family. The patient’s height and weight are at the 56th and 45th percentile for his age, respectively. On physical examination, ambiguous genitalia are present with a bifid scrotum, undescended testicles and hypospadias. Laboratory testing reveals an increased testosterone to dihydrotestosterone ratio. Which of the following is likely true regarding this patient’s parents? 

Memory Anchors and Partner Content

External Links


Content Reviewers

Rishi Desai, MD, MPH


Antonia Syrnioti, MD

Brittany Norton, MFA

Marisa Pedron

Tanner Marshall, MS

5α- reductase deficiency is a genetic disorder in which a protein called 5α reductase is defective or absent.

That’s an enzyme that converts the male hormone testosterone to its more potent form, called dihydrotestosterone.

One of the most important roles of dihydrotestosterone is to help male external genitalia develop in a male fetus.

Okay, normally, very early on in fetal life, male and female internal sex organs and external genitalia are undifferentiated and look identical.

Within the first few months of development, testes develop in the male fetus.

The testes start producing testosterone - a male steroid hormone that belongs to a class of hormones called androgens.

The testosterone gets released into the blood and a tiny fraction of it gets converted by 5α- reductase, which is mainly made in the skin of the genital area, into dihydrotestosterone.

Over time, dihydrotestosterone levels start rising and it affects undifferentiated genital structures.

Looking closely at these structures, at the top there’s the genital tubercle, which is a small projection.

Just below that, there's the urethral groove, which is the external opening of the urogenital sinus or the future urethra and bladder and is surrounded by the urethral folds and the labioscrotal swellings.

Now, once dihydrotestosterone reaches these structures, it makes the genital tubercle elongate into the phallus which will eventually be the penis.

The elongating genital tubercle pulls up the urethral folds which fuse in the midline, forming the spongy or penile urethra.

The tips of the urethral folds remain unfused and that forms the external urethral opening at the distal tip of the penis.


  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "5-alpha-reductase deficiency: a case report" Paediatrica Indonesiana (2016)
  6. "Steroid 5agr-Reductase Deficiency in Man: An Inherited Form of Male Pseudohermaphroditism" Science (1974)

Copyright © 2023 Elsevier, except certain content provided by third parties

Cookies are used by this site.

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.