Estrogen receptor variants and mutations

There is a large and increasing body of experimental and clinical data supporting the existence or variant estrogen receptor (ER) proteins in both normal and neoplastic estrogen target tissues including human breast. Therefore, future examination of ER signal transduction and/or measurement of ER protein must take into account variant ER expression. The functions of variant ER proteins, either physiological or pathological, remain unclear, although a role(s) for some ER variants in breast tumorigenesis and breast cancer progression would be consistent with the accumulated data. Possible tissue specific expression leads to the speculation that ER variants may have a role in tissue specific estrogen action. The following review focuses on the current knowledge available in the scientific literature with respect to the type and characteristics of estrogen receptor variants and mutations that have been identified to occur naturally in tissues and cell lines.

Nonassociation of estrogen receptor genotypes with bone mineral density and estrogen responsiveness to hormone replacement therapy in Korean postmenopausal women

Hormone replacement therapy (HRT) prevents bone loss in postmenopausal women, but some women are resistant to therapy. A recently reported case of severe estrogen resistance caused by a germline mutation at the estrogen receptor (ER) gene locus suggests the possibility that other variants of the ER gene could be responsible for resistance to HRT and could also be an answer to the heritable components of bone density. Three restriction fragment length polymorphisms (RFLPs) at the ER gene locus, represented as BstUI (or B variant), PvuII, and XbaI, and their relationship to bone mineral density (BMD) and estrogen responsiveness to HRT were examined in 248 healthy postmenopausal women, aged 41-68 yr (mean +/- SD, 52.0 +/- 4.6 yr) in Korea. The BstUI restriction site was not found in Korean women. The distribution of the PvuII and XbaI RFLPs was as follows: PP, 35 (14.1%); Pp, 136 (54.8%); pp, 77 (31.1%) and XX, 18 (7.3%); Xx, 72 (29.0%); and xx, 158 (63.7%), respectively (capital letters signify the absence of and lower case letters signify the presence of the restriction site of each RFLP). There was no significant relation between ER genotypes and z score values of lumbar spine BMD. Also, no significant genotypic differences were found in the change in lumbar spine BMD and those in biochemical markers before and after 1 yr of HRT. These data indicate no significant effects of ER genotypes on BMD and estrogen responsiveness after HRT.

Human estrogen receptor messenger RNA variants in both normal and tumor breast tissues

By using the PCR-SSCP technique we characterized various ER-specific RNA species present in a series of primary breast cancers, as well as in cell lines established from breast carcinomas and in mammary gland tissues from healthy specimens. A series of six truncated messenger RNAs generated by alternative splicing was characterized. These RNAs correspond to specific deletions of one (exons 2-7, except exon 6) or two (exons 3 + 4) exons. All these RNA variants are observed in each one of the analyzed RNAs, regardless of origin. In addition, the relative amount of these different variants in ER + tumors is comparable to that measured in ER - tumors and healthy mammary gland tissues. This data suggests that tumor progression is not related to the emergence of any of the ER mRNA variants.

An estrogen receptor genetic polymorphism and the risk of primary and secondary recurrent spontaneous abortion

OBJECTIVE

A case-control study was undertaken to assess the association between an estrogen receptor gene variant and the risk of recurrent spontaneous abortions.

STUDY DESIGN

The frequency of the estrogen receptor gene variant in blood lymphocyte deoxyribonucleic acid and other selected maternal characteristics was compared among 60 primary recurrent aborters, 61 secondary recurrent aborters, and 43 women who had had at least two live births but no spontaneous abortions.

RESULTS

No association was evident between the estrogen receptor gene variant and the risk of either primary or secondary recurrent abortion. There were data suggesting that primary recurrent aborters in particular were more likely to report a family history of recurrent abortion and a family history of breast cancer.

CONCLUSIONS

These findings indicate that the estrogen receptor polymorphism is not a genetic marker for recurrent spontaneous abortions. Therefore, as suggested by previous investigations, this polymorphism appears to be a marker for breast cancer risk only among the subgroups who have had a history of repeated abortions.

Estrogen receptor variant and hypertension in women

Eighty-eight women visiting a gynecologist were tested for an estrogen receptor B-variant allele. The women were ethnically and racially homogeneous to a large degree. They were from a suburb of Long Island, and most were white. The 12% incidence of hypertension in women with the estrogen receptor wild-type allele is comparable to the 13-32% incidence in the general population of women aged 55-64 years. However, the 48% incidence of hypertension in women with the estrogen receptor B-variant allele is considerably higher than in the general population of women in this age group. We conclude that the presence of the estrogen receptor B-variant allele might have increased the prevalence of hypertension in the women in this study.

An estrogen receptor genetic polymorphism and a history of spontaneous abortion--correlation in women with estrogen receptor positive breast cancer but not in women with estrogen receptor negative breast cancer or in women without cancer

We previously identified a polymorphism in the human estrogen receptor gene. In a preliminary study on women with estrogen receptor positive (ER+) breast tumors, we found that the presence of the rarer of the two alleles, the B' allele, is correlated with a history of spontaneous abortion. Because that study evaluated only women with estrogen receptor positive (ER+) breast cancer, it was unknown whether the observed correlation was restricted to the cancer group or was independent of breast cancer. We have now extended our analysis to include not only additional women with ER+ breast cancer, but also those with estrogen receptor negative (ER-) breast cancer and women without cancer. Results of the current study continue to show an association between the B' allele and a history of spontaneous abortion in the ER+ breast cancer group. There was no such correlation either in the ER- breast cancer group or in the group without cancer. Also, we continue to observe, in the ER+ breast cancer group, a significantly higher concentration of ER protein in tumors from homozygous wild type women (genotype BB), than in the tumors from women who are heterozygous for the rarer allele (genotype BB'). We conclude that the combination of spontaneous abortion and the BB' ER genotype may be a marker for breast cancer susceptibility.