Which conditions are associated with a decreased testosterone etiology of microphallus?

Updated: Nov 30, 2020
  • Author: Karen S Vogt, MD; Chief Editor: Sasigarn A Bowden, MD  more...
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In this condition, also known as vanishing testes or testicular regression syndrome, testes are absent in an individual with a normal male karyotype. Micropenis results when testicular degeneration occurs after 12-14 weeks' gestation. The testicular degeneration is likely due to torsion or other vaso-occlusive event in utero. [10, 11]

LH-receptor defects

Autosomal recessive mutations are found in the LHCGR gene in this rare condition and cause Leydig cell hypoplasia in males. The genital phenotype varies from normal-appearing female to male with micropenis. [16, 22]

Defects in testosterone steroidogenesis

Incomplete forms of 17 beta-hydroxysteroid dehydrogenase deficiency type 3 can cause micropenis, but the genitalia are most often female in appearance or less often ambiguous. The enzyme 17-beta-hydroxysteroid dehydrogenase normally converts androstenedione to testosterone. In the deficiency state, the androstenedione-to-testosterone ratio is elevated (after hCG stimulation in the prepubertal state) and is expressed as a testosterone-to-androstenedione ratio of less than 0.8. These individuals undergo profound virilization at puberty. [10, 23, 24]

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