An international team of researchers have identified two genes that are involved in determining when girls begin menstruation.
The researchers from the Peninsula Medical School, Exeter, Britain, along with researchers at institutions in Europe and the United States, studied 17,510 women from across the world, including women of European descent who had started menstruation between nine and 17 years of age.
The researchers say the two genes clarify the genetic control of female sexual maturation and point to regulatory mechanisms involved in human growth and development.
They believe the results of the new study could have ramifications for normal human growth and weight too, because early-age menstruation is also associated with shorter stature and increased body weight - experts say as a rule girls who achieve menstruation earlier in life tend to have greater body mass index (BMI) and a higher ratio of fat compared to those who begin menstruation later.
Reproductive lifespan is closely linked to the risk of developing conditions such as heart disease, breast cancer and osteoporosis and in the western world particularly, children are reaching puberty at younger and younger ages - some girls at the age of seven - the study provides the first evidence that common genetic variants influence the time at which women reach sexual maturation.
Experts suspect that the female sex hormone oestrogen which is produced at higher rates during a woman's reproductive life, raises the risk of these diseases, therefore, the earlier a woman goes through puberty, the more risk she may be at.
The study identified two genes on chromosomes nine and six and they say 1 in 20 females carry two copies of each of the gene variations which result in menstruation starting earlier - these girls will start menstruating approximately four and half months earlier than those with no copies of the gene variants.
Dr Anna Murray from the Peninsula Medical School, says the study provides the first evidence that common genetic variants influence the time at which women reach sexual maturation and also indicates a genetic basis for the associations between early menstruation and both height and BMI.
Dr Murray says the study brings the understanding of the processes involved in puberty and early growth nearer and what constitutes 'normal' growth and development.
Fellow author John Perry, also from the Peninsula Medical School, says understanding the biological mechanisms behind reproductive lifespan may also offer information about associated diseases that affect many women as they age such as diabetes, heart disease and breast cancer.
The research is published in Nature Genetics.