From BBC News:
Scientists say they have begun to crack the genetic code that helps determine when a girl becomes a woman.
A UK-led team located two genes on chromosomes six and nine that appear to strongly influence the age at which menstruation starts.
The Nature Genetics study also provides a clue for why girls who are shorter and fatter tend to get their periods months earlier than classmates.
The genes sit right next to DNA controlling height and weight.
In collaboration with research institutions across Europe and the US, they studied 17,510 women from across the world, including women of European descent who reported reaching menstruation of between nine and 17 years of age.
When they split the women up according to the age they began menstruating, certain gene patterns appeared.
Scanning the whole genome enabled them to hone in on these differences and pinpoint the exact genes most likely accountable.
Three other papers, also published in Nature Genetics, throw up other candidate genes which appear to be involved in the onset of puberty.