What is it about?

Sex hormone binding globulin (SHBG) is involved in delivering sex hormones to target tissues. We investigated the association between the (TAAAA)n repeat polymorphism, and Asp327Asn polymorphism in the SHBG gene with semen quality and idiopathic male infertility. We studied 168 men with idiopathic infertility [oligoasthenoteratozoospermia (OAT)] and equal number of age-matched normal controls.

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Why is it important?

Significant number of infertile men is considered idiopathic due to lack of obvious medical or surgical causes for their infertility. Whilemanysuch cases are attributed to genetic factors, few genetic causes have been confirmed in humans to date. Plasma sex hormone binding globulin (SHBG) binds testosterone and estradiol with high affinity, and selectively transports sex hormones in plasma [5]. SHBG affects the bioavailability of androgens and estrogens and thus their access to target tissues. The SHBG gene is located on chromosome 17p12–p13 and encodes a 402-amino-acid polypeptide. Substantial variations in serum SHBG concentration exist between individuals, and can therefore influence sex hormones actions. A genetic influence on SHBG levels has been well documented [9]. In the last decade, several genetic polymorphisms have been determined in the human SHBG gene.


Previous studies have demonstrated that interindividual differences in circulating SHBG concentrations may in part be genetically determined. Given the role of SHBG in reducing the risk of male infertility and the functionality of the Asp327Asn, and (TAAAA)n repeat polymorphisms in this gene, it is conceivable that men carrying the Asn and short-repeat alleles may be at a reduced risk of infertility. This hypothesis, however, has not been tested in epidemiologic studies. In summary, the results of this study suggested that men with infertility are more frequently carriers of long (TAAAA)n repeat and Asp alleles, in the promoter of the SHBG gene, and these are associated with lower plasma SHBG concentrations. These SHBG polymorphisms were also associated with serum total testosterone and estradiol, and free testosterone, and estradiol, levels in both fertile and infertile men.

Dr Mohammad Reza Safarinejad
University of Medical Sceices

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This page is a summary of: Association of the (TAAAA)n repeat and Asp327Asn polymorphisms in the sex hormone-binding globulin (SHBG) gene with idiopathic male infertility and relation to serum SHBG concentrations, The Journal of Steroid Biochemistry and Molecular Biology, January 2011, Elsevier,
DOI: 10.1016/j.jsbmb.2010.10.005.
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