What is the Origin of (TAAAA)n Polymorphism?

This term originates from molecular genetics and pharmacogenomics, describing a common structural variation in the human genome. The specific (TAAAA)n repeat was identified and characterized in the promoter of the SHBG gene to explain individual differences in circulating SHBG levels. It is an example of a functional polymorphism where a non-coding sequence directly affects gene expression.

What is the Mechanism of (TAAAA)n Polymorphism?

The number of TAAAA repeats dictates the efficiency of the SHBG gene's promoter, thereby regulating the rate at which the gene is transcribed into mRNA. Generally, longer alleles (a greater 'n' value) are associated with reduced transcriptional activity of the SHBG gene. Lower SHBG gene activity leads to lower concentrations of the SHBG protein in the blood. Consequently, this results in higher levels of unbound, biologically active free sex hormones circulating in the body.

(TAAAA)n Polymorphism

Meaning

A specific type of variable number tandem repeat (VNTR) genetic variation is found within the promoter region of the Sex Hormone-Binding Globulin (SHBG) gene. This polymorphism involves the repetition of the pentanucleotide sequence TAAAA, where ‘n’ represents the variable number of these repeats, typically ranging from six to eleven. Different repeat lengths, or alleles, are clinically significant as they influence the gene’s transcriptional activity. The resulting variation in SHBG production can impact the bioavailability of sex hormones like testosterone and estrogen.