New Orleans Scientists attempting to figure out why some girls go through puberty at unusually young ages have found a surprising culprit a gene that speeds up the body's breakdown of the male sex hormone.
Many believe that the age of puberty the time when girls develop breasts and other sexual characteristics is decreasing. The most widely held explanation for this is growing childhood obesity, along with rich diets and lack of physical activity.
However, genes almost certainly play a role in the age of puberty, and many assumed that the most likely players in this scenario would be ones that control the body's production and use of estrogen.
Research released Sunday at a meeting of the American Association for Cancer Research suggests a more complicated interplay of hormones, since the body's supply of testosterone, the male hormone, seems to be a key influence on the timing of puberty.
Dr. Fred F. Kadlubar and colleagues from the Food and Drug Administration's National Center for Toxicological Research discovered the link in a study of 192 girls ages 9 and 10.
A study published four years ago found that about half of all black girls and 15 percent of whites begin to develop sexually by age 8. The average age of puberty is about 13 for whites and a year younger for blacks.
Typically, girls begin breast development about a year before their first period. Kadlubar's team looked for a link between genes and this change in the randomly chosen group of girls.
They examined several genes that control the body's use of estrogen but found no association with early puberty. To their surprise, though, they found a strong link when they tested the girls for a gene that controls the body's breakdown of testosterone.
They looked for a particular variation, called CYP1B1, in a gene that produces a liver enzyme. They found that 90 percent of the girls with two copies of this genetic variation had already begun breast development by age 9 1/2.
It has long been known that estrogen production increases and testosterone falls during this developmental landmark. Kadlubar said the CYP1B1 gene, by reducing testosterone levels, may trigger the cascade of hormones involved in the start of breast development.
Early puberty is a concern, because it increases the risk of breast cancer later in life.
Kadlubar said the enzyme he studied is critically important to the body's well-being, so doctors are unlikely ever to try tinkering with it.