**2.1.2 Single Nucleotide Polymorphism (SNP)**

This involves a single nucleotide which is substituted by a different nucleotide. Typically, SNPs have only two alleles. Since coding DNA accounts for only about 1.5% of the human

Genetic Polymorphisms and Molecular Pathogenesis of Endometriosis 139

Environmental toxic compounds like *dioxin* may increase the risk of endometriosis. Previous association studies implicated GALT gene (a gene involved in galactose metabolism, located on chromosome 9), glutathione S transferases (GSTM 1), (GSTT1), cytochrome p 450 ( CYP1A1) and N- acetyltransferase 2 ( NAT2) genes, which encode for detoxification enzymes, as possible disease susceptibility genes ( Zondervan KT et al, 2001; Hadfield RM et al, OXEGENE collaborative group, 2001; Deguchi M et al, 2005). The diversity of biological effects resulting from exposure to dioxin may reflect the ability of this environmental pollutant to alter gene expression by binding to the Aryl hydrocarbon receptor (AHR) gene

One of the genes previously implicated in endometriosis is CYP17; this encodes the enzyme P450c17alpha, which plays a vital role in steroid biosynthesis in the ovary. However, the CYP17 MspA1 polymorphism has not been associated with endometriosis in either the UK

A study of the association between endometriosis and polymorphisms in the Nacetyltransferase 1 (NAT1) and N-acetyltransferase 2 (NAT2) genes has previously demonstrated a positive association with NAT2 polymorphisms in a UK population. However, polymorphisms in NAT1 and NAT2 were not associated with an increased risk of endometriosis in the Japanese population (Deguchi M et al, 2005).A case control study suggested no association between endometriosis and NAT2 in South Indian-

Glutathione S-transferases (GSTs) are enzymes involved in the metabolism of many diseasecausing carcinogens and mutagens that are present in human environments. An association between the incidence of endometriosis and the GST genotypes of patients has been suggested. The study inferred that GSTM1, GSTT1 and GSTP1 genetic polymorphisms are not associated

*Vascular endothelial growth factor (VEGF),* a major mediator of angiogenesis and vascular permeability, is known to play a key role in the pathophysiology of endometriosis.The single nucleotide polymorphisms, -460C>T and +405G>C, in the 5'-untranslated region of the VEGF gene were associated with lower promoter activity, which was significantly less common in women with endometriosis suggesting that the +405G allele may influence the

A relationship between the *alpha 2-Heremans Schmidt glycoprotein (AHSG)* gene polymorphism and endometriosis has been studied. Women not carrying the AHSG 2 allele were found to have twice the risk of endometriosis there by suggesting an association of endometriosis with the AHSG gene polymorphism in Korean women. (Kim JG et al, 2004).

The risk and severity of endometriosis has been associated with polymorphisms in genes coding for estradiol-synthesizing enzyme like the Ser312Gly polymorphism in 17-beta-

with the development of endometriosis in Korean women (Hur.S.E.et.al, 2005).

likelihood of a woman developing the disease(Bhanoori M et al, 2005).

and related genes (Watanabe T et al, 2001).

women(Arvind-Babu,K.et.al.2005).

**3.2 Angiogenic genes** 

**3.3 Hormonal genes** 

**3.3.1 Estrogen Receptor (ER) gene** 

or the Japanese population(Asghar,T.et.al,2005).

genome, most SNPs are found in the non-coding DNA, such as within introns and intergenic sequences.
