Understanding early puberty
Scientists are struggling to find an explanation for the increasingly early onset of puberty. Up until recently, it was thought that early puberty may be caused by a high-fat diet, lack of physical exercise or exposure to certain chemicals but now scientists believe that there may be a genetic explanation.
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According to a study published in the journal Paediatrics1 in April 1997, girls are reaching puberty much earlier. The average age for breast development and the appearance of pubic hair is just over 9 years for Caucasian girls and 8 years for African-Americans. This study, conducted on 17,077 girls, revealed that puberty begins considerably earlier than previously thought, leading paediatricians to reconsider their definition of precocious puberty.
More recently, a study carried out by the University of Bristol2 on 14,000 children reached the same conclusions. At the age of eight, one in six girls showed early signs of puberty compared to one in 100 a generation ago. This research is particularly significant as the early appearance of (secondary) sex characteristics is considered a risk factor for breast cancer.
What causes early puberty?
There are a number of different, and often rather surprising, hypotheses to explain this phenomenon. For example:
- Being overweight or obese due to a high-fat diet3
- Exposure to sex hormones or pheromones of unrelated adult males4
- Stress of a single-parent family5
- Increase in sexual images on television which fosters sexual maturity (just as the presence or smell of food causes salivation)6
- The exposure to volatile chemicals used in the manufacturing of various plastics that mimic the effects of oestrogen (female sex hormone)7.
But can environmental factors completely explain this early onset of puberty? Could there perhaps be other reasons why this game-console/sex-on- TV/hamburger-loving generation are reaching maturity so much earlier? Well, yes, according to Professor Fred Kadlubar who ascribes a genetic origin to the onset of puberty.
The gene responsible is not the one we originally thought
Professor Kadlubar presented his findings on a study, conducted on 192 girls aged 9-10, to the annual convention of the American Association for Cancer Research (AACR). His initial hypothesis was that the gene or genes controlling the levels of the female hormone oestrogen would be responsible for the onset of early puberty. However, the results of his study failed to establish any such link, despite the apparently sound scientific basis for his hypothesis.
Scientists discovered that it was another gene that was responsible; a gene that produces that a liver enzyme that breaks down testosterone. Ninety per cent of females with two copies of the genetic variation CYP3A4*1B/1B showed signs of breast development at the age of nine and a half, compared to 50% of those who only had one copy and 40% without this genetic variation. Unlike previous studies, these studies did not take account of ethnicity.
According to this study, it is the production of oestrogen, together with the reduction in the concentration of testosterone, caused by this gene, that are responsible for the hormonal changes which stimulate breast development. This finding is important because early puberty is considered a risk factor for breast cancer.
Early puberty a risk factor for breast cancer
Previous studies8 identified early puberty as a risk factor for breast cancer. Following on from this, there are several other areas that would also benefit from additional research.
In the future, would it be useful to carry out genetic screening so as to delay the onset of puberty in some girls? And should other potential risk factors, such as lack of exercise and a high-fat diet, be addressed at the same time? Does this gene similarly affect the sexual development of boys? Further research is needed before we can conclusively answer these questions.
Until then, however, researchers recommend restricting the amount of time spent watching television, encouraging children to play sport and cutting back on visits to fast food restaurants.
1 - Paediatrics 1997 Apr; 99 (4):505-12
2 - Paediatr Perinat Epidemiol 2001 Jan; 15 (1):74-87
3 - Pediatrics 2000 Jul; 106 (1): E14 - Br J Cancer 1999 Apr; 79 (11-12) :1907-11
4 - Child Dev 2000 Mar-Apr; 71 (2) :485-501
5 - Adolescence 2000 Winter; 35 (140) :799-811
6 - Nature. 1999 Oct 21; 401 (6755):763-4
7 - Proceedings of the AACR, Vol.42, March 2001
8 - Cancer Causes Control 2000 May; 11 (5):451-8
Copyright © 2010 Doctissimo
Posted 30.06.2010
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