Abstract for presentation at 11th International Congress of Human Genetics

The age at which menarche occurs in human populations is of significant biological, social and medical interest. Early age at menarche (AAM) has been associated with an increased risk of breast cancer and an increased body mass index. Multiple miscarriages have been associated with both early and late onset of menarche, and AAM has been associated with several social factors such as age at first child and age at marriage. Early AAM has been associated with adolescent behavioural problems. A sample of 1416 Australian female adolescent monozygotic and dizygotic twins and their female siblings were used to investigate genetic influences on recalled AAM. The study design incorporated repeat estimates of AAM given at 12, 14, and 16 years of age. The correlation between AAM estimates given at ages 12 and 14 was 0.89+/-0.06. 279 individuals (20% of the sample) were censored because at the time last seen (usually the 2nd visit around their 14th birthday) their cycle had not yet commenced. Frailty models were used to estimate the variance within zygosity class in the presence of censoring. The proportion of variation in AAM accounted for by the concordance between pairs of twins (R²) was 0.82 and 0.50 for MZ and DZ twin pairs, respectively. A standard twin analysis was carried out, ignoring censoring. An MZ correlation of 0.78 (95%CI: 0.73-0.82) and DZ correlation of 0.59 (95%CI: 0.49–0.68) were estimated, indicating that both genetic factors and common environmental factors contribute to variation in AAM. A further twin analysis was implemented to more accurately account for the censored observations. A linkage analysis is carried out on the 600 individuals in the sample for which marker data was available, and results of the genetic linkage analysis will be presented.