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WEDNESDAY, July 23, 2014 (HealthDay News) -- The timing of a girl's first menstrual period may be determined by hundreds, and possibly thousands, of gene variations, a new study suggests.
Researchers have identified over 100 regions of DNA that are connected to the timing of menarche -- a woman's first menstrual period. The researchers hope these findings will shed light on the biology of a number of diseases ranging from type 2 diabetes to breast cancer.
"These findings will provide additional insights into how puberty timing is linked to the risk of disease in later life," said lead researcher John Perry, a senior scientist at the University of Cambridge MRC epidemiology unit, in the United Kingdom.
Earlier puberty has been linked to increased risks of some of the most common health problems today, including obesity, type 2 diabetes, heart disease and breast cancer. Although estrogen levels are thought to be involved, the full reasons for the connection between menarche and health conditions later in life aren't clear.
The new study found that some of the gene regions linked to menarche overlap with genes tied to hormone production, body weight, weight at birth, adulthood height and bone density -- among other things.
Perry and his colleagues report the findings in the July 23 online issue of Nature.
Combing through data on more than 180,000 women, the researchers found that girls vary widely in the age at which they start menstruating. Some start as early as age 8, while others start in high school. Exercise levels, nutrition and body weight are all influences, but there are probably many other factors involved, too, Perry pointed out.
"We identified over 100 regions of the genome that were associated with puberty timing," he said. "However, our analyses suggest there are likely to be thousands of gene variants -- and possibly genes -- involved."
The implication, Perry said, is that "puberty timing is a much more complex process than we might have originally thought."
Dr. Patricia Vuguin, a pediatric endocrinologist at Cohen Children's Medical Center in New Hyde Park, N.Y., agreed. "Many of these (genes) are completely novel and have never been associated with puberty before," said Vuguin, who was not involved in the study.
Right now, she noted, there is a lot of interest in the factors that influence the timing of puberty -- in part, because children these days are starting puberty at an earlier age, compared with a few decades ago.
The rising tide of childhood obesity is considered a key reason, but studies have found that it's not the whole story.
"But this (study) is saying, it's not that simple," Vuguin said. "It's not only about body fat, or about what you eat. It's much more complicated than that."
One of the big discoveries, according to Perry, was that a "special set" of genes, known as imprinted genes, may help govern puberty timing. With most genes, we inherit one copy from each parent, and both of those copies are active. Imprinted genes are different; only the copy from one parent is active, while the other is "silent."
Researchers have thought that imprinted genes were important only before birth, for fetal growth and development.
"Our study supports the idea that these genes continue to play a role in later-life health and disease," Perry said.
Both he and Vuguin described this study as a first step toward understanding the biology that links puberty timing and health later in life.
One of the limitations of the work is that all of the women were of European descent. But, Perry said he would expect the genes and underlying biology to be "very similar" in women of all races and ethnicities -- and his team is currently studying that question.
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