5-alpha-reductase deficiency


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5-alpha-reductase deficiency


Adrenal gland disorders

Congenital adrenal hyperplasia

Primary adrenal insufficiency

Waterhouse-Friderichsen syndrome


Adrenal cortical carcinoma

Cushing syndrome

Conn syndrome

Thyroid gland disorders

Thyroglossal duct cyst


Graves disease

Thyroid eye disease (NORD)

Toxic multinodular goiter

Thyroid storm


Euthyroid sick syndrome

Hashimoto thyroiditis

Subacute granulomatous thyroiditis

Riedel thyroiditis

Postpartum thyroiditis

Thyroid cancer

Parathyroid gland disorders





Pancreatic disorders

Diabetes mellitus

Diabetic retinopathy

Diabetic nephropathy

Pituitary gland disorders


Pituitary adenoma






Growth hormone deficiency

Pituitary apoplexy

Sheehan syndrome


Constitutional growth delay

Diabetes insipidus

Syndrome of inappropriate antidiuretic hormone secretion (SIADH)

Gonadal dysfunction

Precocious puberty

Delayed puberty

Premature ovarian failure

Polycystic ovary syndrome

Androgen insensitivity syndrome

Kallmann syndrome

5-alpha-reductase deficiency

Polyglandular syndromes

Autoimmune polyglandular syndrome type 1 (NORD)

Endocrine tumors

Multiple endocrine neoplasia

Pancreatic neuroendocrine neoplasms

Zollinger-Ellison syndrome

Carcinoid syndrome



Opsoclonus myoclonus syndrome (NORD)

Endocrine system pathology review

Adrenal insufficiency: Pathology review

Adrenal masses: Pathology review

Hyperthyroidism: Pathology review

Hypothyroidism: Pathology review

Thyroid nodules and thyroid cancer: Pathology review

Parathyroid disorders and calcium imbalance: Pathology review

Diabetes mellitus: Pathology review

Cushing syndrome and Cushing disease: Pathology review

Pituitary tumors: Pathology review

Hypopituitarism: Pathology review

Diabetes insipidus and SIADH: Pathology review

Multiple endocrine neoplasia: Pathology review

Neuroendocrine tumors of the gastrointestinal system: Pathology review


5-alpha-reductase deficiency


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USMLE® Step 1 questions

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High Yield Notes

9 pages


5-alpha-reductase deficiency

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USMLE® Step 1 style questions USMLE

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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? 

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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.


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  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)

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