Genetic correlates of menarcheal age: a multivariate twin study

Heritability of Age at Menarche in Nigerian Adolescent Twins

Heritability of age at menarche (AAM) in African populations remains largely unknown. A question on AAM was given to 1803 [454 monozygotic (MZ), 823 same-sex dizygotic (DZ), and 526 female members of opposite sex] adolescent twins attending public schools in Lagos State, Nigeria. The age range of the sample was 12-18 years, with a mean (SD) of 14.57 (±1.70) years. The data included 905 missing cases consisting of those who had not experienced menarche and did not recall AAM. Missing values were imputed using the Expectation-Maximization algorithm. Kaplan-Meier analysis based on the imputed data yielded 13.23 years [95% CI [13.18, 13.28] for the mean and 13.00 years [95% CI [12.96, 13.04] for the median of AAM. Twin correlation and model-fitting analyses were performed on the basis of those who reported AAM (MZ = 82 complete pairs and 38 cotwin missing cases; DZ = 157 complete pairs and 99 cotwin missing cases). Maximum likelihood MZ and DZ twin correlations for AAM were .63 (95% CI [.48, .74]) and .33 (95% CI [.19, .45]) respectively. Model-fitting analyses indicated that 58% (95% CI [46, 67]) of the variance of AAM was associated with additive genetic influences with the remaining variance, 42% (33-54) being due to nonshared environmental influences including measurement error. The heritability estimate found in this study was within the range of those found in Asian and Western twin samples.

Common Genetic Influences on Age at Pubertal Voice Change and BMI in Male Twins

The present study aimed to explore secular trends in age at voice change (AVC), estimate heritability of AVC and investigate to what extent common genes influence the association between AVC and body mass index (BMI) in South Korean males. The sample of 955 male twins consisted of 241 pairs and 118 co-twin missing monozygotic (MZ) twins, 82 pairs and 50 co-twin missing dizygotic (DZ) twins and 141 male members of opposite-sex DZ twins who participated in telephone surveys in the South Korean Twin Registry. AVC was asked of twins during the surveys. The mean (SD) age of the sample was 18.92 (2.42) years (range: 16.00-29.25 years). The birth years of the twins were divided into two groups (1988-1993, 1994-2001). Kaplan-Meyer survival analyses were conducted to compute the mean age of AVC in the total sample as well as to test mean differences between the two birth cohorts. Maximum likelihood twin correlations and univariate and bivariate model-fitting analyses were performed. The mean AVC in the total sample was 14.19 (95% CI [14.09, 14.29]) years. The mean AVC significantly declined from 14.38 to 14.02 years from 1988 to 2001, confirming downward trends in AVC in recent years. Heritability for AVC was .59 (95% CI [.50, .67]), which was within the range reported in most Western twin studies. Although the phenotypic correlation between AVC and BMI was modest (r = -.14; 95% CI [-.07, -.21]), it was entirely mediated by common genes, similar to what has been found in females in prior twin studies. In conclusion, the present twin study underscores the importance of genetic influences on pubertal timing and its association with BMI in South Korean males.

Heritability of Age at Menarche in South Korean Female Twins

Genetic and environmental influences on age at menarche (AAM) have rarely been examined in Asian females. This study aimed to investigate the heritability of AAM in South Korean female twins. The AAM data from 1370 female twins (933 monozygotic [MZ] twins, 294 dizygotic [DZ] twins and 160 female members of opposite-sex DZ twins) born between 1988 and 2001 were analyzed. The age of the sample at the time of the assessment ranged from 16 to 28 years with a mean of 19.3 (SD = 2.2) years. The mean AAM in the total sample was 12.49 (SD = 1.41) years. Although the mean AAM decreased with increasing birth years, it levelled off in birth years 2000-2001. Maximum likelihood MZ and DZ twin correlations were 0.72 [95% CI (0.67, 0.76)] and 0.35 [95% CI (0.19, 0.50)], respectively. The results of model-fitting analysis indicated that the additive genetic and individual-specific environmental effects were 72% [95% CI (67%, 76%)] and 28% [95% CI (24%, 33%)], respectively. Neither nonadditive genetic nor shared environmental effects were significant.

Genetic Determinants of Prepubertal and Pubertal Growth and Development

This article surveys the current general understanding of genetic influences on within- and between-population variation in growth and development in the context of establishing an International Growth Standard for Preadolescent and Adolescent Children. Traditional genetic epidemiologic analysis methods are reviewed, and evidence from family studies for genetic effects on different measures of growth and development is then presented. Findings from linkage and association studies seeking to identify specific genomic locations and allelic variants of genes influencing variation in growth and maturation are then summarized. Special mention is made of the need to study the interactions between genes and environments. At present, specific genes and polymorphisms contributing to variation in growth and maturation are only beginning to be identified. Larger genetic epidemiologic studies are needed in different parts of the world to better explore population differences in gene frequencies and gene—environment interactions. As advances continue to be made in molecular and statistical genetic methods, the genetic architecture of complex processes, including those of growth and development, will become better elucidated. For now, it can only be concluded that although the fundamental genetic underpinnings of the growth and development of children worldwide are likely to be essentially the same, there are also likely to be differences between populations in the frequencies of allelic gene variants that influence growth and maturation and in the nature of gene–environment interactions. This does not necessarily preclude an international growth reference, but it does have important implications for the form that such a reference might ultimately take.

Genetic Disposition for Global Maturity: An Explanation for Genetic Effects on Parental Report on ADHD

Attention deficit hyperactivity disorder (ADHD) has been shown to be substantially influenced by genetic factors. However it is still not known how these effects are mediated. The aim of this study is to evaluate whether genetic disposition for global maturity could be a mediator of the well-known findings of genetic factors for ADHD symptoms. A total of 1480 pairs of twins aged 8-9 years were identified through the population-based Swedish Twin Registry. A mailed questionnaire with items from DSM-III-R for ADHD and items concerning global maturity were completed by the parents. The results showed that global maturity mediated part of genetic effects for ADHD for both boys and girls. There were also genetic, shared environmental, as well as nonshared environmental effects unique to ADHD not in common with global maturity. Thus, there are at least two pathways through which genetic effects can influence ADHD: one through predisposition for maturational lag and one unique to ADHD, possibly mediated by personality. The results indicate that maturational lag could be of importance for treatment and prognosis of ADHD.

Association analyses suggest the effects of RANK and RANKL on age at menarche in Chinese women

OBJECTIVES

Age at menarche (AAM), the time of the first menstrual bleeding, is an important developmental milestone in the female life. It marks the beginning of the reproductive period. AAM is implicated in the risk of many health complications in later life. In this study, we conducted an analysis for association of single nucleotide polymorphisms (SNPs) and common haplotypes of two candidate genes, RANK (receptor activator of the NF-κB) and RANKL (receptor activator of the NF-κB ligand), with AAM in 825 unrelated Chinese women.

METHODS

In total, 73 SNPs of RANKL and 23 SNPs of RANK were genotyped. The SNPs and common haplotypes were then analyzed for their association with AAM. Age and age( 2 ) were used as covariates.

RESULTS

We found five individual SNPs (rs7239261, rs8094884, rs3826620, rs8089829, and rs9956850) of RANK significantly associated with AAM (p < 0.05). Although no significant association was identified for the RANKL gene, three polymorphisms showed nearly significant (0.05 < p < 0.08) association with AAM. Seven haplotypes of RANK were significantly associated with AAM (p < 0.05); the most significant association of the AT haplotype composed by rs1805034 and rs4524034 (p = 9.4 × 10(-4)) remained significant (p = 0.0235) after the Bonferroni correction for multiple testing. Three haplotypes of RANKL were significantly associated with AAM (p < 0.05). Importantly, the association of rs3826620 replicated our previous findings for Caucasian females.

CONCLUSIONS

The results of the present study suggest that the RANK and RANKL are two candidate genes for AAM in Chinese women.

Evidence for a downward secular trend in age of menarche in a rural Gambian population

Menarcheal age is a key indicator of female maturity and development. Studies in many countries have reported a downward secular trend in age of menarche over the past century. This study presents data gained using the ‘status quo’ method and interval regression to estimate median menarcheal age of girls in a rural Gambian community. Cross-sectional studies carried out in 1989, 2000 and 2008 revealed a median menarcheal age of 16.06 (95% CI 15.67–16.45), 15.03 (95% CI 14.76–15.30) and 14.90 (95% CI 14.52–15.28), respectively. The average rate of decline of median age of menarche was amongst the most rapid yet reported, at 0.65 years of age per decade (p < 0.00001). There was no evidence for a change in the rate of decline over the two decades studied. These results probably reflect ongoing socio-economic development within the region.

TNFRSF11A and TNFSF11 are associated with age at menarche and natural menopause in white women

OBJECTIVE

Menarche and menopause mark the lower and upper limits of the female reproductive period. The timing of these events influences women's health in later life. The onsets of menarche and menopause have a strong genetic basis. We tested two genes, TNFRSF11A (RANK) and TNFSF11 (RANKL), for their association with age at menarche (AM) and age at natural menopause (ANM).

METHODS

Nineteen single nucleotide polymorphisms (SNPs) of TNFRSF11A and 12 SNPs of TNFSF11 were genotyped in a random sample of 306 unrelated white women. This sample was analyzed for the association of the SNPs and common haplotypes with AM. Then, a subsample of 211 women with natural menopause was analyzed for the association of both genes with ANM. Smoking, alcohol intake, and duration of lactation were applied as covariates in the association analyses.

RESULTS

Three polymorphisms of TNFSF11 were associated with AM: rs2200287 (P = 0.005), rs9525641 (P = 0.039), and rs1054016 (P = 0.047). Two SNPs of this gene, rs346578 and rs9525641, showed an association with ANM (P = 0.007 and P = 0.011, respectively). Two SNPs of TNFRSF11A were associated with AM (rs3826620; P = 0.022) and ANM (rs8086340; P = 0.015). Multiple SNP-SNP and SNP-environment interaction effects on AM and ANM were detected for both genes. One polymorphism of TNFRSF11A, rs4436867, was not directly associated with either trait but indicated significant interactions with four TNFSF11 polymorphisms on ANM. Two other TNFRSF11A polymorphisms, rs4941125 and rs7235803, showed interaction effects with several TNFSF11 polymorphisms on AM. Both genes manifested significant interaction with the duration of breast-feeding in their effect on ANM.

CONCLUSIONS

The TNFRSF11A and TNFSF11 genes are associated with the onset of AM and ANM in white women.

Association analyses suggest multiple interaction effects of the methylenetetrahydrofolate reductase polymorphisms on timing of menarche and natural menopause in white women

OBJECTIVE

This study aimed to investigate whether polymorphisms of the methylenetetrahydrofolate reductase (MTHFR) gene are associated with age at menarche and age at natural menopause in white women.

METHODS

In a cross-sectional study, a total of 305 randomly selected unrelated white women were genotyped for six single nucleotide polymorphisms (SNPs) of the MTHFR gene (including one common replacement, rs1801133). This sample was comprehensively analyzed for the association of the SNPs with age at menarche. Then a subsample of 210 women who experienced natural menopause was analyzed for the association of the MTHFR gene with age at natural menopause.

RESULTS

Duration of breast-feeding was a significant predictor of earlier natural menopause (P < 0.05). No individual SNPs were associated with either age at menarche or age at natural menopause. However, three significant (P < 0.05) SNP-SNP interaction effects (rs2066470/rs1476413, rs2066470/rs4846049, and rs17037390/rs4846049) on the onset of menarche were determined. Three haplotypes were significantly associated with age at menopause (P < 0.05). Four SNPs (rs2066470, rs17037390, rs1801133, and rs4846048) indicated significant interaction effects with various lifestyle factors on age at natural menopause.

CONCLUSIONS

The results of our study suggest that the MTHFR gene may influence the onset of menarche and natural menopause. This effect is probably due to the multiple SNP-SNP and SNP-environment interactions. More independent studies are needed to further clarify the possible contribution of this gene to the timing of menarche and menopause.

Variability of reproductive history across the Swiss SAPALDIA cohort – Patterns and main determinants

BACKGROUND

Reproductive characteristics play an aetiological role for many diseases, including reproductive cancers. They have been shown to vary internationally and nationally, but have not yet been described for the whole Swiss population.

AIM

The study investigated the variability of reproductive characteristics, their patterns, and main determinants across a population-based female study population in Switzerland.

METHODS

Reproductive characteristics obtained from 3119 women (28-72 years) participating in the SAPALDIA cohort survey in 2001-2003 are described across birth cohorts, study areas, language regions, and levels of urbanization. Determinants of age at menopause were analysed by Cox regression.

RESULTS

Reported median age at menarche was 13 years and median age at natural menopause was 52 years. The prevalence of nulliparity was 27%, and the fertility rate 1.6. Across birth cohorts there was a decline of menarcheal age and fertility rates, and an increase of nulliparity and age at last pregnancy. All characteristics varied across study areas, language regions, and levels of urbanization. Smoking, parity, and physical exercise were stronger predictors of earlier (<52 years) than older (>52 years) menopausal age.

CONCLUSION

Reproductive events show secular and geographic variation within Switzerland. Smoking, parity and physical activity significantly predict age at natural menopause, particularly before age 52. The secular trend of earlier menarche and increased nulliparity may result in a higher risk of reproductive cancers in younger generations.

Timing of menarche, childbearing and hysterectomy risk

OBJECTIVES

To examine the associations of age at menarche, timing of first birth and parity with hysterectomy rates; to investigate whether these associations were independent of each other and other potential confounders and varied by reason for hysterectomy.

METHODS

Women from the Medical Research Council National Survey of Health and Development, a cohort followed prospectively since birth in March 1946 across England, Scotland and Wales, were studied. Survival analyses were used to assess the relationships between reproductive characteristics and hysterectomy.

RESULTS

Age at menarche was inversely associated with hysterectomy rates (adjusted Hazard Ratio for hysterectomy associated with a 1 year increase in menarche=0.85 (95% CI: 0.77-0.95)). Parity was also associated with hysterectomy; women with > or =3 children experienced higher rates of hysterectomy than women with 1-2 children, who themselves experienced higher rates than nulliparous women. The associations of parity and age at menarche with hysterectomy were independent of each other and potential confounders. The association between age at menarche and hysterectomy was stronger for hysterectomies performed for fibroids than for other reasons.

CONCLUSIONS

Our findings suggest that age at menarche is most likely acting to influence hysterectomy risk through its association with lifetime oestrogen exposure whereas parity is most likely acting through an effect on decision-making processes. This highlights the importance of considering both biological and social pathways to hysterectomy and confirms that medical need is not the only factor which needs to be considered when making treatment decisions for gynaecological problems.

Genetics of pubertal timing and its associations with relative weight in childhood and adult height: the Swedish Young Male Twins Study

OBJECTIVE

Previous studies have suggested that the timing of puberty is associated with BMI in childhood and adult stature. Because the genetic background of these associations is not thoroughly investigated, we aimed to analyze it in a longitudinal twin cohort.

METHODS

We studied a Swedish cohort of 99 monozygotic and 76 dizygotic twin pairs born between 1973 and 1979 with weight and length or height measured annually from birth to age 18 years. Age at onset of pubertal growth spurt, age at peak height velocity, and final height were estimated by a parametric JPA2 growth model. The genetic architecture and mutual associations of these traits and childhood BMI were analyzed by linear structural equation modeling.

RESULTS

The heritability estimate was 0.91 for age at onset of pubertal growth spurt, 0.93 for age at peak height velocity, and 0.97 for adult height. Age at onset of pubertal growth spurt was negatively associated with BMI from 1 to 10 years of age and stature in early adulthood. For age at peak height velocity, we found similar associations with childhood BMI and stature in early adulthood. These associations were explained by common genetic factors.

CONCLUSION

Growth during puberty is strictly genetically regulated. These genetic factors also explain why boys who matured early had higher BMI through childhood and taller stature in early adulthood.

Estimation of variance components for age at menarche in twin families

Age at menarche (AAM), time of first menstrual period, is an important developmental milestone in females. Follow-up data from 1,302 adolescent twins and their sisters were used to partition the normal variation in AAM. The proportion of censoring was 14.1%. Both a standard and a survival analysis method were used. The best fitting model from the survival analysis method was an ACE model, where 57% and 23% of the variance in AAM was explained by additive genetic and environmental effects, respectively. The best fitting model when using a standard variance decomposition method was an AE model, where 82% of the variance was explained by additive genetic effects. The lack of correspondence between the results of the two methods was an artefact of the different ascertainment of AAM reports from siblings and twins. After the removal of the sibling sample, both methods indicated that an ACE model was the most likely. Standard and survival analysis methods estimated the proportion of variance explained by additive effects to be 0.50 and 0.54, and common environmental effects to be 0.31 and 0.29, respectively. We conclude that variation in AAM can be explained by additive genetic and common environmental components.

Reproductive and menopausal factors and risk of systemic lupus erythematosus in women

OBJECTIVE

Systemic lupus erythematosus (SLE) occurs predominantly in women, and hormones may play a role in its etiology. This study was carried out to examine associations between female reproductive and menopausal factors and the development of SLE.

METHODS

A cohort of 238,308 women was prospectively examined. Subjects were older women (ages 30-55 years at start) and younger women (ages 25-42 years at start) from the Nurses' Health Study (NHS) and NHSII cohorts. Incident SLE diagnosed between 1976 and 2003 was confirmed by medical record review. The relative risk (RR) of SLE was estimated separately in each cohort using Cox proportional hazards models, and then pooled using meta-analysis random effects models.

RESULTS

Two hundred sixty-two incident cases of SLE were confirmed among the women. In multivariable models adjusted for reproductive and other risk factors, age<or=10 years at menarche (pooled RR 2.1, 95% confidence interval [95% CI] 1.4-3.2), oral contraceptive use (pooled RR 1.5, 95% CI 1.1-2.1), and use of postmenopausal hormones (RR 1.9, 95% CI 1.2-3.1) significantly increased the risk of SLE. An elevation of SLE risk was observed among postmenopausal women primarily after surgical menopause (RR 2.3, 95% CI 1.2-4.5), and also among women with earlier age at natural menopause (P for trend<0.05). Menstrual irregularity was associated with an increased risk of SLE among women in the younger (NHSII) cohort. Age at first birth, parity, and total duration of breastfeeding were not associated with SLE.

CONCLUSION

Early age at menarche, oral contraceptive use, early age at menopause, surgical menopause, and postmenopausal use of hormones were each associated with an increased risk of SLE. These associations may point to the mechanisms underlying the pathogenesis of SLE.

Heritability of age at menarche in girls from the Fels Longitudinal Study

Menarche is the hallmark maturational event of female childhood. Many studies indicated a significant genetic contribution to the timing of the onset of menstruation, but most of these studies were limited by the use of retrospective data and by the use of data from only certain types of relatives (i.e., mothers and daughters, sisters, or twin sisters). The primary goal of this study was to use a modern maximum likelihood quantitative genetic method to estimate the heritability (h(2)) of age at menarche, using familial data collected over the course of the 74-year-old Fels Longitudinal Study. The secondary goal was to review earlier studies of the heritability of age at menarche. The study of the heritability of age at menarche presented here is unique for two reasons. First, because of the Fels Longitudinal Study's serial design, age-at-menarche data were collected prospectively from most participants. Second, because the Fels Longitudinal Study is a family study that has been conducted for decades, age-at-menarche data are available from many types of female relatives spanning multiple households and generations. The best-fitting and most parsimonious quantitative genetic model included provision for a secular decrease in age at menarche, and estimated the h(2) of age at menarche to be 0.49+/- 0.13 (95% confidence interval of h(2),=0.24-0.73). The results of this study are in general agreement with the findings of most previous studies of genetic influences on age at menarche, and suggest that it is reasonable to consider it well-established that approximately half the phenotypic variation among girls from developed nations in the timing of menarche is due to genetic factors.

Determination of sequence variation and haplotype structure for the gonadotropin-releasing hormone (GnRH) and GnRH receptor genes: investigation of role in pubertal timing

Because GnRH and its receptor (GnRHR) are pivotal regulators of the reproductive endocrine axis and mutations in GNRHR lead to hypogonadotropic hypogonadism, we investigated whether genetic variation in GNRHR or GNRH1 affects pubertal timing in the general population. To screen for missense mutations in these genes that might affect pubertal timing, we resequenced the coding regions of these genes in 48 probands with late but otherwise normal pubertal development. No missense variants were found in either gene, except for a previously identified single nucleotide polymorphism (SNP) in GNRH1 that was not associated with late pubertal development. To search for common variants that might affect pubertal timing, we took a haplotype-based association approach. To identify common haplotypes in these genes, we genotyped 41 SNPs in DNA from commercially available European-derived multigenerational pedigrees and participants in a multiethnic cohort (MEC). Two blocks of strong linkage disequilibrium were identified that spanned GNRHR and one was identified spanning GNRH1; within each block, more than 80% of chromosomes carried one of a few common haplotypes. A set of haplotype-tagging SNPs that mark these common haplotypes in all five ethnic groups within the MEC were defined and used to perform association studies among 125 trios (probands with late pubertal development and their parents) and 506 women from the MEC who had early (menarche < 11 yr of age, n = 216) or late (menarche > or = 15 yr of age, n = 290) pubertal development. Three SNPs in GNRHR showed modest association with late pubertal development in the trios; among the 506 women, a different SNP was associated with late menarche, and one rare haplotype was associated with early age of menarche. All of the observed associations were relatively modest and only nominally statistically significant; replication is needed to determine their validity. We conclude that genetic variation in GNRH1 and GNRHR is not likely to be a substantial modulator of pubertal timing in the general population.

Genetic and environmental influences on pubertal development: longitudinal data from Finnish twins at ages 11 and 14

To study sources of individual differences in pubertal development, the authors fit a sex-limitation common factor model to data reported, at ages 11 and 14 years, by 1,891 twin pairs on items that comprise the Pubertal Development Scale (PDS; A. C. Petersen, L. Crockett, M. Richards, & A. Boxer, 1988). The model divides variation into a general pubertal factor and item-specific variation and, in addition, decomposes it into constituent sources. In both boys and girls, genetic influences made the largest contribution to variance common to PDS items. Genetic and nonshared environmental factors accounted for variation specific to PDS items in boys, whereas for girls, common environmental influences were added for growth spurt and menarcheal status. For both common and item-specific variation, genetic effects were partially sex specific. Subsidiary analyses found accelerated maturation in both boys and girls who at age 14 were reared in father-absent homes.

Longitudinal estimates of puberty timing in Senegalese adolescent girls

This study aimed to assess the timing of sexual maturation (breast development and menarche occurrence) among sub-Saharan African adolescent girls from rural areas. In the framework of a longitudinal study of growth at puberty, the stages of pubertal development (Tanner classification) and menarche occurrence were recorded at intervals between 1995 and 2000 in a sample of 406 Senegalese adolescent girls from a rural area. Nutritional status was estimated during infancy, childhood, and adolescence within this sample, and body composition was estimated only during adolescence. At the beginning of the study (1995), the adolescent girls were 11.4 years old (SD = 0.6). At the end of the study, they were 16.5 years old (SD = 0.6). Median and quartile ages at entry into each maturity stage and its confidence limits were estimated by a lognormal parametric survival model. These adolescent girls were shorter and thinner than girls of the same age from developed countries. Median age at the onset of breast development was 12.6 years (95% CI = 12.5-12.8). Median age at the end of sexual maturation and median age at menarche were estimated respectively at 15.8 years (95% CI = 15.7-15.9) and 15.9 years (95% CI = 15.7-15.9). These adolescent girls were less mature than other adolescent girls of the same age from other developing countries. Their puberty was extremely delayed compared to that of adolescent girls of the same age from industrialized countries. Puberty in these Senegalese adolescent girls is delayed by about 3 years. This may be due to malnutrition, significant energy expenditure, and poor diet and living conditions, and possibly to genetic control.

Secular trends in age at menarche among Caboclo populations from Pará, Amazonia, Brazil: 1930-1980

The present study is part of a large research project on growth, development, nutrition, and health of Caboclo populations from the Brazilian Amazon. The aim of this paper is to analyze the age of menarche in adolescents (N=164) and adult women (219) in the studied populations. Caboclo are admixed rural, peasant groups that live along the Amazon river and its tributaries, and there are few previous studies about them. Probit analysis of the status quo data yielded a median age at menarche of 12.29+/-1.76 years. The retrospective method was applied to recall data of the 77 post-menarcheal adolescents, yielding an average of 13.06+/-1.27 years. Number of children in the family did not show any statistical influence on age at menarche in any age group. In adult women, age at menarche decreased from 14.50 in those born in 1930 to 12.88 for those born in 1980 (F=4.371, P=0.001). The downward trend found was, on average, 0.237 year per decade in the study period. The median age at menarche in the adolescents (12.29 years) is one of the lowest values found for Central and South American populations. In the ecological context, a low age at menarche could be an adaptive advantage because it provides a greater chance for reproduction at a young age in an environment where, until recently, life expectancy was low. As has been reported for other developing countries, the change found in age at menarche in the women born from the 1930s to the 1980s is likely to be related to changes in health and nutritional factors that occurred in Brazil because this country experienced significant improvement in living standards related to education, vaccination, and health conditions, which, although not equally, reached all regions after the 1960s.

Genetic approaches to stature, pubertal timing, and other complex traits

The factors that regulate the timing of puberty remain largely elusive, as do the factors that modulate childhood growth and adult height. However, it is clear that these developmental processes are highly heritable--much of the natural variation in growth and timing of puberty is due to genetic variation within the population. In this review, we discuss how recent genetic and genomic advances can be exploited to help understand the genetic regulation of these processes. In particular, we describe how genome-wide linkage scans and association studies, in conjunction with haplotype-based approaches, are potentially useful tools to increase our understanding of these two complex traits. Discovery of the genetic variants that regulate these two traits would expand our understanding of human neuroendocrinology, postnatal development, and the general architecture of complex genetic traits.

Age at menarche in Coimbra (Portugal) school girls: a note on the secular changes

The age at menarche and several menstrual symptoms were reported by 516 Portuguese school girls who took part in a cross-sectional anthropometric study in Coimbra, Portugal. The mean ages of menarche calculated using the recall method and also using probit analysis were 12.53 +/-1.27 and 12.03 +/- 1.26 years, respectively. Parents'educational level, place of residence and size of the family did not have any significant effect on the mean age at menarche in this sample of adolescents. The order of birth was the only variable that indicated a significative effect: the first borns reported a lower mean age at menarche (12.34 years) than the later borns (12.6 years). In this sample, 47% of the girls had a cycle length of >or = 29 days, 23.4% had irregular cycles, 59% reported that the duration of bleeding was 3-5 days and the majority, 49%, did not report any pain during the bleeding days. However, 14.3% and 24.45% reported severe and medium pain. The age at menarche has declined from 15.0 (girls born in 1880-1890) to 12.03 (girls born in 1970-1980) years in the Portuguese population. This decrease in age, and also the lack of influence of the family characteristics, appear as a result of the great improvements in the social and economic living conditions that occurred in Portugal, especially after the 1970s. These improvements are mainly related to better nutrition and better health care along with many other environmental factors.

Social background and age at menarche in Portuguese university students: a note on the secular changes in Portugal

Menarcheal age of a sample of Portuguese university students (n = 3366), born between 1972 and 1983, age 18-23 years, was analyzed. The influence of parents' educational level and occupation, family size, birth order, and degree of urbanization of girl's locality of residence during childhood and adolescence were analyzed as well as secular trend in the Portuguese population. Mean age at menarche for girls born in 1983 was 12.32 years. Parents' educational level and occupation did not show any significant influence on mean age at menarche. Place of residence during childhood years and adolescence showed a significant effect on mean age at menarche, with girls from rural places with a later age at menarche than those who spent their childhood or adolescence in urban areas (P <or= 0.01 and P <or= 0.05 for childhood and adolescence, respectively). Family size and birth order showed the highest effect. Girls born in small families, with one child, matured earlier (12.32 years) than those born in large families with four or more children (12.67 years), (P <or= 0.01). Also, girls that were first-born had an earlier menarche (12.41 years) than those who were third or later (12.58 years, P <or= 0.01). Regression analysis selected family size and place of residence in childhood as the most important determinants of mean age at menarche in our university students. In this sample, from 1972 to 1983, mean age at menarche remained stable. When we considered published data from all the Portuguese population we found a decrease in mean age at menarche from 15 years for girls born in 1880 to 12.44 for those born in the 1980s. This decrease was the result of great improvements in the social and economic living conditions that occurred in Portugal especially after the 1970s concerning nutrition and health care, among many other environmental factors.

A multigene test for the risk of sporadic breast carcinoma

BACKGROUND

Although the identification of the BRCA1 and BRCA2 genes have been of great interest, these genes account for less than 5% of all breast carcinoma cases. The remaining cases are sporadic. Reanalysis of a large twin study suggested that genetic factors may play a significant role in sporadic breast and other carcinomas. Sporadic breast carcinoma is polygenically inherited. Multiple genes are likely to have an additive effect, each gene accounting for a fraction of the variance. One factor that may have an impact on the development of hormonally responsive breast tumors is the duration of exposure of the breast to estrogen. Therefore, one of the demographic risk factors for breast carcinoma is an early age of onset of menarche. The current study was based on the hypothesis that genes that play a role in demographic risk factors may be breast carcinoma risk genes in their own right. The authors hypothesized that six genes relevant to the timing of the onset of menarche and related risk factors might be candidate genes for breast carcinoma. These were the leptin gene (LEP), the leptin receptor gene (LEPR), the catechol-0-methyltransferase gene (COMT), the dopamine D(2) receptor gene (DRD2), the estrogen 1 receptor gene (ESR1), and the androgen receptor gene (AR).

METHODS

The authors examined 67 women with postmenopausal sporadic breast carcinoma and 145 gender and race-matched controls.

RESULTS

Five of these genes accounted for a significant percent of the variance (r(2)) of breast carcinoma. The following r(2) and P values were calculated: LEP: 0.073, P < or = 0.0001; LEPR: 0.064, P < or = 0.0002; COMT: 0.073, P < or = 0.0001; AR: 0.040, P < or = 0.0035; and DRD2: 0.018, P < or = 0.05. When evaluated in a multivariate regression analysis, they accounted collectively for 24% of the variance of breast carcinoma (P < or = 0.0001). These genes accounted for 40% of the variance (P < or = 0.00001) in a subset of age-matched cases. Individual gene scores were added to form a breast carcinoma risk score (BCRS) that ranged from 0 to 17. When the BCRS was evaluated in a receiver operator characteristic plot, the area under the curve was 0.80 for the full set and 0.869 for the age-matched set. The relative breast carcinoma risk for the different BCRS scores ranged from 0.10 to 11.9.

CONCLUSIONS

These results demonstrate a potentially powerful method of evaluating the additive effect of multiple breast carcinoma risk genes to form a potentially clinically useful assessment of women's risk for sporadic breast carcinoma.

Secular trends in growth

Since the 19th century there have been clearly documented secular trends to increasing adult height in most European countries, with current rates of 10-30 mm/decade. Over the same period menarcheal age has also fallen steeply, but has now stabilized at approximately 13 years and may be rising again. Height trends tend to be greater in childhood than in adulthood due to the associated advance in maturation, but no trends are apparent before the age of 2 years. In particular, birth-weight trends are small and different in shape from height trends. The adult height trend matches that at age 2 years, so that the increment in adult height has already been achieved by age 2 years. To try to identify factors relating to the secular trend, increased height gain in late infancy is hypothesized to be equivalent to a reduction in stunting, and stunting is thought to be caused by impaired growth in the long bones of the leg in later infancy. Leg growth may be regulated by the expression of growth-hormone receptors on the growth plates, which it is hypothesized are susceptible to the interaction between concurrent nutrition and the nominal growth rate set during pregnancy. The timing of menarche is also likely to be determined by some growth factor operating near the time of birth, which also affects later weight, but not height.