Tuesday, August 6, 2013

Researchers Describe New Genetic Causes of Isolated Micropenis

AR mutations may cause micropenis
Newly identified mutations in the AR gene may cause micropenis

In this post we will examine a study named "Isolated 'idiopathic' micropenis: hidden genetic defects?" that was published in 2011, in the International journal of Andrology. In this study, the authors discovered that isolated micropenis may also be the result of some previously unknown mutations in the AR and SF1 genes.

The study first mentions that the etiologies behind the micropenis condition vary and include:
  • Androgen resistance 5α-reductase 5αR deficiency
  • Defects in testosterone synthesis
  • Growth hormone deficiency (GHD)
  • Hypogonadotropic hypogonadism (also known as secondary or central hypogonadism)
  • Partial androgen insensitivity 
  • Testicular dysgenesis
  • Some other rare cause
  • Yet to be discovered causes
  • A combination of the above

Purpose of this study was to determine whether micropenis in patients with normal testosterone levels is the result of some hidden molecular defect in the androgen pathway that had yet to be described. 

A total of 26 boys with isolated micropenis enrolled for the study. All participants presented with:
  • 46XY karyotype
  • Normal levels of the luteinizing hormone (lutropin) and follicle-stimulating hormone
  • Normal levels of testosterone in their plasma 

During the study, the researchers sequenced the Androgen receptor (AR) and  5αR and the steroidogenic factor 1 (SF1) genes. 

A micropenis (more micropenis images)

Results
The researchers reported that they found a mutation in the AR gene in two of the patients, and a previously unknown mutation in the SF1 gene in one patient who also had a low level of inhibin B (InhB).

Conclusions
The authors reported that this is the first study to show that isolated micropenis may be the result of mutations in the AR and SF1 genes adding that "Anti-Mullerian hormone and InhB should thus be evaluated in patients with isolated micropenis, even when plasma testosterone is in the normal range." 

Reference
Paris F, De Ferran K, Bhangoo A, Ten S, Lahlou N, Audran F, Servant N, Poulat F, Philibert P, & Sultan C. (2011) Isolated 'idiopathic' micropenis: hidden genetic defects?. International journal of andrology, 34(6 Pt 2). PMID: 21535007

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