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Hum. Reprod. Advance Access originally published online on October 6, 2005
Human Reproduction 2006 21(2):554-557; doi:10.1093/humrep/dei326
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© The Author 2005. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Combined estrogen receptor {alpha} and estrogen receptor beta genotypes influence the age of menarche

I. Stavrou1, C. Zois1, A. Chatzikyriakidou2, I. Georgiou2 and A. Tsatsoulis1,3

1 Department of Endocrinology and 2 Laboratory of Reproductive Genetics, University of Ioannina, 45110 Ioannina, Greece

3 To whom correspondence should be addressed. E-mail: atsatsou{at}cc.uoi.gr


    Abstract
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 Acknowledgements
 References
 
BACKGROUND: Age at menarche has a strong genetic influence. We reported recently an association between the XbaI (351A->C)and PvuII (397T->C) polymorphisms of the estrogen receptor (ER){alpha} gene with the age of menarche in Greek adolescents. In the present study, we examined whether ERbeta genotypes alone, or in combination with ER{alpha} genotypes, may also influence onset of menarche. METHODS: We performed genotyping for the single nucleotide polymorphisms 1730A->G and 1082G->A of the ERbeta gene and examined their association with the age of menarche in the same cohort of 145 Greek girls. We then looked for a possible effect of combined ER{alpha} and beta genotypes on the age of menarche. RESULTS: Menarche occurred 7 months later in girls with the AA genotype of the 1730A->G polymorphism than in girls with the AG genotype (mean ± SD: 13.23 ± 1.24 versus 12.66 ± 1.26 years, respectively; P = 0.005). The 1082G->A polymorphism was not detected in any of the girls examined. A significant effect of combined ER{alpha} and beta genotypes was also apparent. Menarche occurred 11 months later in girls bearing the AA/TT,AA (ER{alpha}, ERbeta) genotypes compared with girls with the CC/CC,AG genotype (13.30 ± 1.27 nersus 12.41 ± 1.28 years; P = 0.042). The difference remained significant after adjusting for body mass index (P = 0.034). CONCLUSION: Combined ER{alpha} and ERbeta polymorphisms may influence the age of menarche.

Key words: estrogen receptor {alpha}/estrogen receptor beta/genotypes/genetic polymorphisms/menarche


    Introduction
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 Acknowledgements
 References
 
Menarche depends on the maturation and co-ordination of the hypothalamic–pituitary–ovarian axis with the female reproductive system and other endocrine organs, including the adipose tissue (Carr, 1998Go). The timing of menarche is regulated by a variety of environmental and genetic factors. Family and twin studies have indicated that the genetic contribution may be more important than environmental effects, since 53–74% of the variation in age of menarche can be attributed to genetic factors (Sharma, 1983Go, van den Akker et al., 1987Go, Treloar and Martin, 1990Go, Kaprio et al., 1995Go). However, the specific genes involved in this event are not yet well defined.

More than 30 years ago, Frisch and McArthur (1974)Go proposed that a given amount of body fat is necessary before the onset of menstrual cycles. This claim was recently substantiated by establishing that leptin constitutes the permitting signal, informing the brain on the amount of energy stored in adipose tissue (Kiess et al., 2000Go; Mantzoros, 2000Go) and that a polymorphic variant of the leptin gene may influence the onset of menarche in interaction with maternal age (Comings et al., 2001Go).

Ovarian estrogens appear to play an important role in the differentiation, maturation and function of the reproductive system—and also, in females, the distribution of adipose tissue—through endocrine and paracrine effects mediated by the activation of estrogen receptors (ER) (Enmark and Gustafsson, 1999Go). Two such receptors have been identified, ER{alpha} and ERbeta. Both subtypes have been found in the female reproductive organs with overlapping but not identical tissue distribution, and with different or complementary contribution to reproductive functions (Kuiper et al., 1996Go, Enmark et al., 1997Go).

Polymorphic variants of both ER{alpha} and ERbeta genes have been identified in recent years and studied for possible association with reproductive and other clinical outcomes (Georgiou et al., 1999Go; Syrrou et al., 1999Go; Weel et al., 1999Go). Such allelic variants could also account for the genetic variability in the age of menarche. Indeed, we have recently shown that two polymorphisms of the ER{alpha} gene, in particular XbaI (351A->C) and PvuII (397T->C) may influence the age of menarche in healthy adolescent Greek girls (Stavrou et al., 2002Go).

In the present study, we examined the association of 1082G->A and 1730A->G polymorphisms of the ERbeta gene with the age of menarche and their potential interaction with ER{alpha} genotypes in influencing this event in the same study population.


    Materials and methods
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 Acknowledgements
 References
 
Subjects
The study population consisted of 145 healthy adolescent girls from a closed rural community in northwest Greece as described previously (Stavrou et al., 2002Go). This homogeneous population was selected with the anticipation that environmental and cultural heterogeneity, which could possibly create some variability in the age of menarche, would be minimal. Information on the age of menarche was taken through personal interviews with the adolescents and their mothers. Informed consent of the girls and their parents, and approval of the study by the University Hospital of Ioannina Ethics Committee were obtained.

Genotyping
Details on genomic DNA extraction and genotyping for the XbaI (351A->C) and PvuII (397T->C) polymorphisms (Herrington and Howard, 2003Go) of the ER{alpha} gene have been described previously (Stavrou et al., 2002Go).

Genotyping for the 1082G->A (Sundarrajan et al., 2001Go) and 1730A->G (Kealey et al., 2001Go) polymorphic variants of the ERbeta gene was carried out as follows. Specific DNA amplification was performed by PCR using 1 unit of recombinant Taq DNA polymerase (Gibco BRL, Göteborg, Sweden) in DNA thermocycler PTC-100 (Peltier-Effect Cycling, MJ Research, Watertown, Massachusetts, USA). The ligand binding domain of exon 5 and the 3'-untranslated region of exon 8 of the ERbeta gene were amplified using the following primer pairs: 5'-TCTTGCTTTCCCCAGGCTTT-3', 5'-ACCTGTCCAGAA CAAGATCT-3' and 5'-GACCTGCTGCTGGAGATGCT-3', 5'-AAT GAGGGACCACACAGCA-3', respectively.

PCR products were analysed for RFLP using RsaI and AluI restriction enzymes (Gibco BRL). Nucleotide exchange G–A at nucleotide 1082 in exon 5 created a recognition site for RsaI, and exchange A->G at nucleotide 1730 in the 3' untranslated region of exon 8 introduced a recognition site for AluI (Fig. 1). Enzyme digestion products underwent electrophoresis on 2% agarose gel and the separation patterns were photographed under ultraviolet illumination. The resulting genotypes for RsaI (1082G->A) and AluI (1730 A->G) polymorphic sites were characterized as GG, GA, AA and AA, AG, GG, respectively.


Figure 1
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Figure 1. The gene encoding estrogen receptor beta (ERbeta) with the positions of known polymorphisms

 

To meet quality control standards and avoid genotyping errors, all samples were run in duplicate and read by two investigators independently. In addition, genotyping was repeated in 20% of randomly selected samples. There was full agreement between the two investigators reading the gels.

Statistical analysis
The t-test and one-way analysis of variance (ANOVA) were used for comparison conducted in Advanced Statistics Package for Social Sciences (SPSS Inc., Chicago, IL, USA). All P-values are two-tailed and P < 0.05 was considered significant.


    Results
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 Acknowledgements
 References
 
Association of ERbeta genotypes with the age of menarche
The overall mean ( ± SD) age at menarche was 12.92 ± 1.26 years; this is a figure typical for the rural population of this region. Of note, heterozygotes for the ERbeta 1730A->G polymorphism were over-represented, whereas homozygotes for the presence of the polymorphic site were not detected, deviating from Hardy–Weinberg equilibrium (P = 0.005). Regarding the ERbeta 1082G->A polymorphism, only one genotype (GG) was present in our population study. A similar deviation from Hardy–Weinberg equilibrium was observed for the ER{alpha} 351A->C and 397T->C polymorphisms as previously reported by Stavrou et al. (2002)Go. This is highly suggestive of the presence of genetic drift that can be observed in closed communities, as was the case for our study population.

This was further substantiated by comparing the observed allele frequencies (Table I) with allele frequencies derived from other populations. Thus, frequencies in the order of 37– 64% and 94–99% for the A allele of the ERbeta 1730A->G and the G allele of the 1082G->A polymorphisms, respectively, have been described in other populations (Rosenkranz et al., 1998Go; Lambert et al., 2001; Arko et al., 2002Go). With regard to ER{alpha} 397T->C and 351A->C polymorphisms, the frequencies for the T and A alleles were 53.4% and 43.4%, respectively, whereas in the general Greek population these are 48% and 41.5% (I.Georgiou, N.Xita, L.Lazaros, unpublished observation).


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Table I. Demographic characteristics of the study population and frequency of the different estrogen receptor beta (ERbeta) genotypes

 

Menarche occurred 7 months later in girls with the AA genotype (mean ± SD: 13.23 ± 1.24 years) than in girls with the AG genotype (12.66 ± 1.26 years) of the ERbeta 1730A->G polymorphism (P = 0.005).

Effect of combined ER{alpha} and ERbeta genotypes on the age of menarche
Since ER{alpha} and ERbeta genes may interact in their biological effects on reproductive functions, we investigated whether combined genotypes of both ER{alpha} 351A->C and 397T->C and ERbeta 1730A->G polymorphisms may also influence the age of menarche. As shown in Table II, girls bearing the AA/TT haplotype of ER{alpha} polymorphisms in combination with the AA genotype of ERbeta (Group 1) had 11 months delay in menarche compared with girls bearing the genotype combination CC/CC,AG (Group 2). In addition, menarche occurred 4 months later when girls in Group 1 were compared with girls carrying all other genotype combinations (Group 3). The differences were significant when the groups were compared with each other (P = 0.04). There appeared to be a trend for earlier onset of menarche for girls carrying one or more of the polymorphic C/C,G alleles of ER{alpha} and ERbeta, respectively—the greater the number of these alleles, the earlier the age of menarche.


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Table II. Comparison for age at menarche between different estrogen receptor {alpha} (ER{alpha})and estrogen receptor beta (ERbeta) genotype combinations

 

After adjusting for BMI (recorded at the time of evaluation), the difference in menarcheal age between AA homozygotes and the AG heterozygotes for the 1730A->G polymorphism was still significant (P = 0.006). Similarly, the difference in age of menarche between the girls with the genotype combination AA, AA/TT in Group 1 compared with the groups 2 and 3 remained the same (P = 0.034).


    Discussion
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 Acknowledgements
 References
 
Family and twin studies have shown that genetic factors are related to age of menarche. Thus, significant correlations between age at menarche in mothers and daughters along with significant differences in menarcheal age between monozygotic and dizygotic twin pairs have been described (Treloar and Martin, 1990Go). We reported recently that age at menarche was associated with the XbaI (351A->C) and possibly the PvuII (397T->C) polymorphism of the ER{alpha} gene in healthy adolescent Greek girls (Stavrou et al., 2002Go). In particular, menarche occurred 6 months later in girls with the AA genotype of the 351 A->C polymorphism than in girls with AC or CC genotypes and tended to occur later in TT homozygotes of the 397T->C polymorphism than in TC and CC genotype carriers. In the current study, we examined whether there was also an association between ERbeta genotypes and age at menarche in the same study population, since ERbeta receptors are also distributed in reproductive tissues and may influence reproductive function (Kuiper et al., 1997Go; Hiroi et al., 1999Go; Sar and Welsch, 1999Go; Pelletier and El-Alfy, 2000Go).

The gene encoding ERbeta is located in chromosome 14q 22–24 (Enmark et al., 1997Go). Five novel polymorphisms have been identified so far within the ERbeta gene (Rosenkranz et al., 1998Go). Among these, two silent mutations, 1082 G->A within exon 5 (RsaI polymorphism) and 1730 A->G in the 3'-untranslated region of exon 8 (AluI polymorphism) were selected in the present study, since these polymorphisms have been implicated in other conditions where estrogen exposure is considered to be an important risk modifier (Rosenkranz et al., 1998Go; Eastwood et al., 2002Go).

In our study, the 1082G->A polymorphic variant was not found in any of the girls examined, indicating that this polymorphism may be rare in Greek or South European populations. With regard to 1730A->G polymorphism, however, AA homozygotes appeared to delay menarche by 7 months compared with heterozygotes for the polymorphism indicating that, in addition to ER{alpha} genotypes, ERbeta genotypes may also contribute to genetic variability of the age of menarche.

In our study, we aimed for a population that would have homogeneity for cultural parameters and environmental influences. The lack of Hardy–Weinberg equilibrium for both ER{alpha} and ERbeta polymorphisms also suggests that this is a closed community with probably considerable genetic drift due to inbreeding in small communities (Rousset and Raymond, 1995Go; Vogel and Motulsky, 1997Go).

Previous studies have shown significant associations of the 1082G->A and 1730A->G polymorphisms with reproductive dysfunctions (Sundarrajan et al., 2001Go). In addition, the 1082G-> A polymorphism has been associated with anorexia nervosa (Rosenkraz et al., 1998; Eastwood et al., 2002Go).

Although the above polymorphisms do not lead to amino acid changes in the ERbeta protein, it is possible that this polymorphism is in linkage disequilibrium with other regulatory sequence variations that may affect gene expression or function (Yaich et al., 1992Go). Alternatively, it is believed that single nucleotide polymorphisms—even when situated in the untranslated region—may cause different structural folds of mRNA, and thus influence the expression of the gene (Shen et al., 1999Go).

The second hypothesis we tested in this study was whether combined genotypes of both ER{alpha} and ERbeta polymorphisms may also influence the age of menarche. This hypothesis was based on the knowledge that, in addition to homodimers, functional ER{alpha}/ERbeta heterodimers may interact in their biological effects (Cowley et al., 1997Go). Indeed, we observed a positive additive effect of combined 351A->C, (397T->C) (ER{alpha}) and 1730A->G (ERbeta) genotypes on the age of menarche. In particular, the AA/TT haplotype of ER{alpha} combined with the AA genotype of ERbeta is associated with later onset of menarche by 11 months compared with the genotype combination CC/CC,AG. Furthermore, there appeared to be a trend for earlier menarche for the girls with one or more of the polymorphic C/C,G alleles of the respective genes in that, the higher the number of these alleles, the earlier the onset of menarche—suggesting a dose-response effect. This implies that ER{alpha} and ERbeta genes may interact in their effects on the age of menarche and this effect may be modified by the presence of certain genotype combinations of both ER subtypes.

Significant interactions between the ERbeta 1730A->G polymorphism and the ER{alpha} 351A->C and 397T->C polymorphisms were also reported in a study on Alzheimer’s disease in the U.K (Lambert et al., 2001Go). This study suggested that the risk for Alzheimer’s disease may be modulated by certain ER{alpha} and ERbeta variants, which influence their expression and/or biological activities.

In conclusion, the findings of the present study suggest that the 1730A->G polymorphism of the ERbeta gene is associated with the age of menarche among healthy adolescent girls. In addition, combined genotypes of both ER{alpha} and ERbeta polymorphisms may further influence menarcheal age, suggesting interaction between these two ER subtypes in affecting this event. Thus, allelic variants of both ER{alpha} and beta genes may contribute to the genetic variability in the age of menarche.


    Acknowledgements
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 Acknowledgements
 References
 
We are grateful to Dr T. Trikalinos (Laboratory of Hygiene and Epidemiology, University of Ioannina) for his help and support during statistical analysis.


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 Introduction
 Materials and methods
 Results
 Discussion
 Acknowledgements
 References
 
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Submitted on May 14, 2005; resubmitted on August 13, 2005; accepted on September 9, 2005.


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