New Delhi, Jul 1 (IANS): An international team of scientists has identified genes that can indirectly influence the age at which girls have their first period by accelerating weight gain in childhood.

The team led by the University of Cambridge studied the DNA of around 800,000 women from Europe, North America, China, Japan, and Korea.

Their results, published in the journal Nature Genetics, showed more than 1,000 variants -- small changes in DNA -- that influence the age of the first menstrual period. Around 600 of these variants were observed for the first time, the team said.

Normally periods occur between ages 10 to 15, but this has been getting earlier and earlier in recent decades.

While the reasons are not fully understood, the study found that 45 per cent of the discovered genetic variants affected puberty indirectly, by increasing weight gain in early childhood.

"Many of the genes we've found influence early puberty by first accelerating weight gain in infants and young children. This can then lead to potentially serious health problems in later life, as having earlier puberty leads to higher rates of overweight and obesity in adulthood," said Professor John Perry, at the varsity’s Medical Research Council (MRC) Epidemiology Unit.

The scientists also analysed rare genetic variants that are carried by very few people, but which can have large effects on puberty. For example, they found that one in 3,800 women carry variants in the gene ZNF483, which caused these women to experience puberty on average, 1.3 years later.

Dr. Katherine Kentistou, lead study investigator said that the team "identified six genes which all profoundly affect the timing of puberty".

Besides causing early onset of periods in girls, these genes often had "the same impact on the timing of puberty in boys".