Vol. 06 Issue 1, Winter 2001
Ivelisse Colon, PhD, Doris Caro, PhD,
Carlos J. Bourdony, MD, FAAP, and Osvaldo Rosario, PhD
Puberty/Breast Development: When is Premature?
In humans, the onset of puberty is primarily assessed by the physical changes that occur in the genitalia of both sexes. In females, the physical signs associated with the onset of puberty are enlargement of the breasts, ovaries, and uterus, as well as the growth of pubic and axillary (armpit) hair with apocrine secretion (sweat with odor). The process by which puberty occurs is primarily regulated by the endocrine system through its chemical messengers, specifically the sexual hormones (Liwnicz, B.H. and R.G. Liwnicz, 1989). The onset of pubertal changes at an earlier age than expected may occur secondary to a varied group of disorders. When the cause of premature sexual development is unknown, the condition is considered idiopathic (having no known cause). Premature sexual development in the human female is presently defined as the appearance of any physical change characteristic of puberty with onset before eight years of age (Sippell, 1994; Stanhope, 2000). Hyperplasia (increased but non-cancerous growth) of breast tissue in newborns may be present during the first six months of life as a result of placental passage of maternal estrogenic hormones. When this condition persists beyond this period or occurs before eight years of age in females, it is known as premature or precocious thelarche (figure 1). The majority of cases occur before two years of age. Girls diagnosed with premature thelarche have one or both breasts enlarged without any other physical signs of the onset of puberty (Kulin and Muller, 1996; Stanhope, 2000).
Premature Thelarche in Puerto Rico
Since 1979, pediatric endocrinologists in Puerto Rico have detected an alarming increase in the number of patients with premature thelarche (Pérez, 1982; Bongiovanni, 1983). Among the hypotheses proposed to explain the observed premature sexual development in this US Caribbean island territory, the most controversial theory associated thelarche with the subject's diet. Sáenz et al. (1985) suggested that dairy and meat products were contaminated with anabolic estrogenic chemicals, which are used for increasing muscle mass in cattle and poultry. In 1985, studies conducted by the US Department of Agriculture, in conjunction with a scientific commission from the Puerto Rico Department of Health, led to the conclusion that no abnormal levels of the suspected chemicals were present in the approximately 800 samples of meat and dairy products that were analyzed (Montgomery, unpublished data). Other theories are still under consideration, such as the association with ovarian cysts, premature endogenous production of sexual hormones, and environmental contamination by pharmaceutical waste products. These theories do not establish a strong association with the majority of the cases reported (Freni-Titulaer, et al., 1986). Also, a genetic predisposition of Puerto Rican girls for developing premature thelarche is unlikely. Investigation of this ethnic group in the Philadelphia area did not reveal a similar pattern of early sexual development (Freni-Titulaer, et al., 1986). Moreover, other ethnic groups living in Puerto Rico are also affected by the condition (Freni-Titulaer, et al., 1986).
In 1987, the Puerto Rico Department of Health created by law the Premature Thelarche and Early Sexual Development (PTESD) Registry in response to the observed increase in cases (Commonwealth of Puerto Rico, 1989). This is the only world registry created for the study of premature sexual development in a human population. The objectives of this surveillance system are to define the epidemiologic, clinical, and etiologic aspects of the different manifestations of premature sexual development on the island. Although the registry was established in 1988, retrospective data to 1969 and prospective data to 2001 have been collected. In this time period, approximately 7,600 cases of premature sexual development have been registered, of which 70% are premature thelarche cases. Based on the data accumulated by the registry, the estimated annual average incidence rate of premature thelarche in Puerto Rican girls 6-24 months of age is eight cases per 1,000 live female births from 1984 to 1993 (Bourdony, 1998). This incidence is, to our knowledge, the highest ever reported. Compared to a study conducted in Minnesota (Van Winter, et al., 1990), this estimated incidence of premature thelarche in the Puerto Rican female population is 18.5 times higher. The actual incidence is much higher since only the cases diagnosed by some of the pediatric endocrinologists practicing in the island are being recorded by the Registry. The other 30% of registered cases consist of premature sexual hair, strong (apocrine) odor in both sexes, vaginal bleeding in females and prepubertal enlarged breasts (gynecomastia) in males. No studies have been conducted to define the clinical, epidemiologic, etiologic or prognostic characteristics of these conditions.
Exploring an Environmental Connection
In the last decade, there has been a growing interest and concern for the study of the impact of man-made chemicals on wildlife and humans. These studies have suggested that synthetic and naturally occurring substances in the environment may affect the normal function of the endocrine system. These substances are also referred to as endocrine disrupting chemicals (EDCs). In wildlife, alterations in sexual reproductive behavior have been observed in areas of contamination with EDCs. For example, malformations in the sexual organs of alligators have been reported in Lake Apopka, Florida, where high concentrations of DDT and its degradation products have been detected (Guillette, et al., 1994; Vonier, et al., 1996). Feminization of male trout in the Great Lakes has been associated with the high levels of polychlorinated biphenyls (PCBs) in water samples (Colborn, et al., 1993). Other studies have indicated that many chemicals, including phthalate esters, may affect development and reproduction, including germ cells, sperm motility, chryptorchidism, and hypospadias in laboratory animals (Siddiqui and Srivastava, 1992; Fredricsson et al., 1993; Imajima, et al., 1997; Poon, et al., 1997; Arcadia, et al., 1998). The specific mechanisms by which these chemicals may affect human health are mostly unknown. Extrapolations to humans of the effect of these substances on wildlife are difficult. A limited number of reports (Mocarelli, et al., 1996; Weisglas-Kuperus, et al., 1995; Sattin, et al., 1984) in the scientific literature describe the accidental exposure of humans to chemicals such as lindane and other organochlorine pesticides, dioxins, and PCBs with known endocrine disrupting properties. The study of these exposures has led to the conclusion that these compounds can alter the female-to-male ratio in offspring (Mocarelli, et al., 1996) and cause learning disabilities, behavioral problems, suppression of the immune system, and gynecomastia (abnormal enlargement of the male mammary glands) in the exposed subjects (Weisglas-Kuperus, et al., 1995; Sattin, et al., 1984).
At present, the cause of the observed high incidence of premature sexual development in Puerto Rico is unknown, and the long-term consequences of the aberrant premature sexual development in this population are also unknown. Many of the chemicals that are classified as EDCs have been imported or produced in high quantities in Puerto Rico. Until 1988, a total of 450 million pounds of chlorinated pesticides were imported to the island (Quiñones, 1992). Although many of these pesticides are currently banned for use in US territories, these pesticides are known to bioaccumulate and to persist in the environment. Also, many of these substances such as phthalate esters, alkyl phenols, and surfactants are present in commercial products commonly used for packaging, storing, and preserving food (Ross, 1994). The environmental load of plasticizers in Puerto Rico is unknown, but is assumed to be significant because of the high level of consumption of dietary products in plastic containers imported to the island. Based on the high exposure to these substances in the general population in Puerto Rico and the fact that exposure of human fetuses, newborns, and young girls to exogenous estrogenic chemicals may lead to adverse effects in their sexual development, in 1997 we designed a study to search for known EDCs in the serum of Puerto Rican girls with premature thelarche and controls (Colón, et al., 2000). Significant high levels of phthalates [dimethyl, diethyl, dibutyl, and di-(2-ethylhexyl) and its major metabolite mono-(2-ethylhexyl) phthalate] were identified in 28 (68%) samples from thelarche patients. Of the control samples analyzed, only one showed significant levels of di-isooctyl phthalate. The phthalates that we identified have been classified as endocrine disruptors. This study suggests a possible association between plasticizers with known estrogenic and antiandrogenic activity, and the cause of premature breast development in a human female population.
Among the observations that may arise to explain the results that we have obtained in our study is the possible contamination during collection or analysis of the patient samples. It is well known that phthalates are ubiquitous in the environment and such contamination can occur unless particular care is observed to avoid it. With this possibility in mind, the experimental procedures were designed to assure that all the control samples were obtained, stored, handled and analyzed in exactly the same conditions as the patient samples. The presence of EDC phthalates were not observed in the control samples. Had the source of the EDC phthalates in the patient samples been due to contamination, these too would have been detected in the controls. In addition, synthetic serum matrix samples, known commercially as Monitrol, were used as blanks to monitor the overall procedure. No contamination was observed in these blanks. In addition to the evidence from the controls and the blanks previously described, to further discard possible contamination, metabolites of the phthalates were also analyzed and detected in the study samples. Had contamination of the samples been the source, the metabolites would not be detected since the metabolites are formed when phthalates esters are internalized in the patient.
Where Do We Go From Here?
The findings of this study cannot be interpreted as the specific cause of premature thelarche in Puerto Rican girls. It may well be that the etiology of the various manifestations of premature sexual development (including thelarche) on this island is multifactorial. Further research should be performed to clarify if phthalate esters by themselves, or in association with other endogenous or exogenous estrogenic compounds, are capable of inducing precocious sexual development in animals and humans.
In the last century, the average age of menarche in the US and Europe has decreased by two to three months per decade, probably as a result of improved nutrition and living conditions (Marshall and Tanner, 1989). In a study conducted by the American Academy of Pediatrics in 1997 that included 17,077 girls, Herman-Giddens et al. (Herman-Giddens, et al., 1997) reported that girls in the United States are developing pubertal characteristics at younger ages than previously reported, but the age of menarche was not significantly reduced. These authors concluded that "the possibility that the increasing use of certain plastics and insecticides that degrade into substances that have estrogen-related physiological effects on living things should be investigated in relation to the earliest onset of puberty". Is the observation of premature sexual development in Puerto Rico a more prominent manifestation of a wider US or world phenomenon? The answer to this important hypothesis awaits confirmation by future research.
There is growing concern that premature thelarche may not be the homogeneous or benign medical condition that it was once considered (Stanhope, 2000). A descriptive analysis of 1,196 cases from Puerto Rico revealed that 73% of the girls (under two years of age) had "classical" thelarche as compared to the rest (two to eight years of age) which conformed more to an atypical variant as classified by Stanhope (Stanhope, 2000; Larriuz, 1998). This study also revealed that in Puerto Rico, girls under two years of age with premature thelarche have a hormonal profile characterized by increased LH (luteinizing hormone) and estradiol (one of the naturally-occurring estrogens) levels. This finding suggests some degree of endogenous activation of the mechanisms of puberty in this cohort, in the absence of all the physical characteristics of complete sexual development. The possible association of early exposure to estrogens in young girls and development of breast cancer later in life is currently under scientific scrutiny. The long-term sequelae of premature thelarche have not been adequately studied and defined. Preliminary data suggest several possible complications like progression to central precocious puberty, ovarian cyst formation, and development of benign or malignant tumors of the breast (Stanhope, 2000). The possible associations of other physical or psychological sequelae to thelarche cases in Puerto Rico have not been adequately studied. Unfortunately, the problem of premature sexual development in Puerto Rican children is not a priority health issue for the island's health authorities, pediatric professional associations and health research centers. This may explain why, although this important public health observation has been known for more than two decades, its etiology, long term consequences, and prevention still await elucidation. Is the increased occurrence of premature sexual development in Puerto Rico (and in particular premature thelarche) a natural phenomenon, a public health catastrophe induced by environmental man-made toxicants, or a combination of these two factors? The elucidation of this biologic enigma should prove to be of important scientific and public health value for improving the health care of children in Puerto Rico, but also for further understanding the future of sexual development in humans.
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Address correspondence to:
Dr. Osvaldo Rosario
Department of Chemistry, University of Puerto Rico
P.O. Box 23346
San Juan, Puerto Rico 00931-3346
Telephone: (787) 764-0000, ext. 7367
Fax: (787) 763-6899