Several weeks ago, I commented on the ways new diagnoses and definitions have changed our view of autism, and how the statistics about autistic disorders have been affected by the way we define them. Today I want to discuss another phenomenon of development that looks different depending on the way we define it. This aspect of development is "precocious puberty" , the markedly early maturation of reproductive organs and secondary sexual characteristics to the adult levels that make reproduction possible. I should note that the treatment of precocious puberty, when it is needed, is naturally a medical issue; however, understanding of the timing of puberty is based on research in developmental science. How early is early?
Reproductive maturity does not occur overnight (thank goodness!), and there is usually a period of puberty, the run-up to maturity, that lasts a year or more. This period of time involves developmental changes such as spurts in height and later in weight and the growth of hair in the groin and armpits. In boys, the penis and scrotum grow larger. Girls begin with a series of changes in the breast area: an elevated area around the nipple, called the "breast bud", followed by increased development of breast tissue. The beginning of menstruation follows breast development and depends in part on the proportion of fat in the girl's body which must reach the amazing level of 22% before menstruation begins.
The average ages at reproductive maturity are a little under 13 years for girls and a little under 15 years for boys in the United States. Keep in mind: when we say "average", we mean a number we calculate by adding up, for example, the ages of a large group of girls at the time of their first menstruations, and dividing that sum by the number of girls. It's very possible that no one of those girls will have had her first period at exactly the age which is the average. It's certainly true that most of the girls will have had their first periods at quite different ages than the average. If we made a graph of the ages of all the girls at first menstruation, we would see the familiar "bell-shaped" distribution, with many of the girls close to the average age, and fewer with ages at first menstruation that are either much higher or much lower than the average.
Once we do the arithmetic to find the average and describe the age distribution, we now have a more difficult problem: to decide the normal range, and to define precocious puberty as reproductive maturation that occurs earlier than the lowest age in that normal range. For many years, precocious puberty in girls was defined as involving breast development before age 8. (As you can well imagine, defining and assessing development in boys is not quite so easy, so much of the work on this matter has studied girls.) However, more recent studies (Kaplowitz, P. . Precocious puberty in girls and the risk of a central nervous system abnormality: The elusive search for diagnostic certainty: Commentary. "Pediatrics", Vol. 109, pp. 139-141) have reported that early development of breast tissue is not as uncommon as we might expect. One author reported that by 8 years of age 25% of girls of African ancestry and 8% of girls of European ancestry have some breast tissue.
Although there are clear social and psychological concerns about precocious puberty, the most serious reason for paying attention to early development is the possibility that this growth is driven by abnormalities in the child's central nervous system. However, Kaplowitz, the author mentioned earlier, referred to a French study in which girls under 6 who showed signs of precocious puberty were compared to girls between 6 and 8. About 6% of the younger children did have some central nervous system problem, but only 2% of those over 6 had. This suggests that girls showing precocious puberty between 6 and 8 years of age probably do not need further evaluation for nervous system problems. Precocious puberty in boys, defined as development before age 9, is quite rare (1 in 10,000 in the United States), but when it does occur is much more often associated with central nervous system problems that need treatment.
As you can see, the diagnosis of a child with precocious puberty would depend on the definition used in the diagnosis. The old definition of precocious puberty in girls as involving development before age 8 would make for more diagnoses among girls between 6 and 8 than the more recent view, whereas diagnoses among girls younger than 6 would not be affected.
Incidentally, there have been some reports that adopted children are more likely to experience precocious puberty. In one case known to me, an adoptive mother managed to treat her 12-year-old adopted daughter with the drug Lupron, although the girl's pediatrician had assured her that puberty at that age is far from precocious; I hope this woman's misunderstanding did not come from popular beliefs about adoption spread by Internet discussion. Some research on this matter has suggested that precocious puberty is more common among children who have experienced rapid growth catch-up following an earlier period of malnutrition, but it is also possible that in the absence of birth records such children's ages have been underestimated because of their small size and skeletal differences. A recent longitudinal study, following children over some years of growth, found no cases of precocious puberty in 36 children adopted from Romanian orphanages (Lemare, L., & Audet, K. (2006). A longitudinal study of the physical growth of postinstitutionalized Romanian adoptees. "Paediatrics and Child Health", Vol. 11, pp. 85-91).