Niels E Skakkebaek

Publications of Niels E Skakkebaek

• Lower birth weight and increased body fat at school age in children prenatally exposed to modern pesticides: a prospective study.

  Authors: Christine Wohlfahrt-Veje, Katharina M Main, Ida M Schmidt, Malene Boas, Tina K Jensen, Philippe Grandjean, Niels E Skakkebæk, Helle R Andersen

  Environmental health : a global access science source. 09/2011; 10:79.

  Endocrine disrupting chemicals have been hypothesized to play a role in the obesity epidemic. Long-term effects of prenatal exposure to non-persistent pesticides on body composition have so far notEndocrine disrupting chemicals have been hypothesized to play a role in the obesity epidemic. Long-term effects of prenatal exposure to non-persistent pesticides on body composition have so far not been investigated. The purpose of this study was to assess possible effects of prenatal exposure to currently used pesticides on children's growth, endocrine and reproductive function. In a prospective study of 247 children born by women working in greenhouses in early pregnancy, 168 were categorized as prenatally exposed to pesticides. At three months (n = 203) and at 6 to 11 years of age (n = 177) the children underwent a clinical examination and blood sampling for analysis of IGF-I, IGFBP3 and thyroid hormones. Body fat percentage at age 6 to 11 years was calculated from skin fold measurements. Pesticide related associations were tested by linear multiple regression analysis, adjusting for relevant confounders. Compared to unexposed children birth weight and weight for gestational age were lower in the highly exposed children: -173 g (-322; -23), -4.8% (-9.0; -0.7) and medium exposed children: -139 g (-272; -6), -3.6% (-7.2; -0.0). Exposed (medium and highly together) children had significantly larger increase in BMI Z-score (0.55 SD (95% CI: 0.1; 1.0) from birth to school age) and highly exposed children had 15.8% (0.2; 34.6) larger skin folds and higher body fat percentage compared to unexposed. If prenatally exposed to both pesticides and maternal smoking (any amount), the sum of four skin folds was 46.9% (95% CI: 8.1; 99.5) and body fat percentage 29.1% (95% CI: 3.0; 61.4) higher. There were subtle associations between exposure and TSH Z-score -0.66(-1.287; -0.022) and IGF-I Z-score (girls: -0.62(-1.0; -0.22), boys: 0.38(-0.03; 0.79)), but not IGFBP3. Occupational exposure to currently used pesticides may have adverse effects in spite of the added protection offered to pregnant women. Maternal exposure to combinations of modern, non-persistent pesticides during early pregnancy was associated with affected growth, both prenatally and postnatally. We found a biphasic association with lower weight at birth followed by increased body fat accumulation from birth to school age. We cannot rule out some residual confounding due to differences in social class, although this was adjusted for. Associations were stronger in highly exposed than in medium exposed children, and effects on body fat content at school age was potentiated by maternal smoking in pregnancy.

• Sperm counts, data responsibility, and good scientific practice.

  Authors: Niels E Skakkebaek, Anna-Maria Andersson, Anders Juul, Tina Kold Jensen, Kristian Almstrup, Jorma Toppari, Niels Jørgensen

  Epidemiology (Cambridge, Mass.). 09/2011; 22(5):620-1.

• Proceedings of the 7th Copenhagen Workshop on Testicular Carcinoma in situ and Germ Cell Cancer, 13-15 October 2010.

  Authors: Ewa Rajpert-De Meyts, Kenneth M Grigor, Niels E Skakkebaek

  International journal of andrology. 08/2011; 34(4 Pt 2):e1.

• Pathogenesis of testicular carcinoma in situ and germ cell cancer: still more questions than answers.

  Authors: Ewa Rajpert-De Meyts, Niels E Skakkebaek

  International journal of andrology. 08/2011; 34(4 Pt 2):e2-6.

• Klinefelter syndrome: the forgotten syndrome: basic and clinical questions posed to an international group of scientists.

  Authors: Anders Juul, Lise Aksglaede, Katrine Bay, Ken M Grigor, Niels E Skakkebaek

  Acta paediatrica (Oslo, Norway : 1992). 06/2011; 100(6):791-2.

• Clinical and biological parameters in 166 boys, adolescents and adults with nonmosaic Klinefelter syndrome: a Copenhagen experience.

  Authors: Lise Aksglaede, Niels E Skakkebaek, Kristian Almstrup, Anders Juul

  Acta paediatrica (Oslo, Norway : 1992). 03/2011; 100(6):793-806.

  Klinefelter syndrome (KS) is the most frequent sex chromosome disorder in males, but the phenotype varies greatly and is therefore highly under-diagnosed. We aimed at describing the phenotypicKlinefelter syndrome (KS) is the most frequent sex chromosome disorder in males, but the phenotype varies greatly and is therefore highly under-diagnosed. We aimed at describing the phenotypic characteristics throughout life from clinical follow-up of our large cohort of patients with KS. A retrospective observational study of 166 males with nonmosaic 47,XXY KS aged 0.3-80.3 years. Data on phenotype, growth, body composition, bone mineral density, sex hormones, lipids, glycosylated haemoglobin (HbA1C) and prostate-specific antigen were recorded. In addition, histological examination of testicular biopsies from 29 patients was performed. Patients with Klinefelter were taller already in childhood. All patients had smaller testicular volume and elevated luteinizing hormone (LH) and follicle-stimulating hormone levels in adulthood. Cryptorchidism was reported in 14%, gynaecomastia in 44%, and 36% required speech therapy or educational support. The abnormal biochemical parameters became evident after onset of puberty and correlated with histological findings of a gradual deterioration of seminiferous tubules and massive Leydig cell hyperplasia in adults. Our patients presented with a wide spectrum of the classical Klinefelter symptoms. In adulthood, two features were consistently present in every patient: small testes and high LH/testosterone ratio, often despite normal testosterone levels. Such biochemical parameters combined with small testes should lead to a suspicion of KS.

• Urinary excretion of phthalate metabolites in 129 healthy Danish children and adolescents: estimation of daily phthalate intake.

  Authors: Hanne Frederiksen, Lise Aksglaede, Kaspar Sorensen, Niels E Skakkebaek, Anders Juul, Anna-Maria Andersson

  Environmental research. 03/2011; 111(5):656-63.

  Phthalates are a group of chemicals with widespread use in the industrial production of numerous consumer products. They are suspected to be involved in male reproductive health problems and havePhthalates are a group of chemicals with widespread use in the industrial production of numerous consumer products. They are suspected to be involved in male reproductive health problems and have also been associated with several other health problems in children including obesity and asthma. To study the urinary excretion of phthalate metabolites in Danish children recruited from the general population, and to estimate the daily intake of phthalates in this segment of the population. One 24 h urine sample and to consecutive first morning urine samples were collected from 129 healthy Danish children and adolescents (range 6-21 yrs). The concentrations of 11 phthalate metabolites of 5 different phthalate diesters were analyzed by liquid chromatography-tandem mass spectrometry. The analyzed metabolites were detectable in almost all 24h urine samples. The median concentrations of monoethyl phthalate (MEP), monobenzyl phthalate (MBzP) and the sums of the two monobutyl phthalate isoforms (∑MBP(i+n)), metabolites of di-(2-ethylhexyl) phthalate (∑DEHPm) and of di-iso-nonyl phthalate (∑DiNPm) were 29, 17, 111, 107 and 31 ng/mL, respectively. The youngest children were generally more exposed to phthalates than older children and adolescents (except diethyl phthalate (DEP)). Boys were more exposed than girls. The median estimated daily intake of phthalate diesters was: 4.29 (dibutyl phthalate isoforms (DBP(i+n))), 4.04 (DEHP), 1.70 (DiNP), 1.09 (DEP) and 0.62 (butylbenzyl phthalate (BBzP)), all calculated as μg/kg body weight/24h. Between 40% and 48% of the absolute amount of phthalate metabolites excreted over 24h were excreted in first morning urine voids. Danish children are exposed simultaneously to multiple phthalates. The highest exposure levels were found for DBP(i+n) and DEHP, which in animal models are the known most potent anti-androgenic phthalates. The combined exposure to the two isoforms of DBP, which have similar endocrine-disrupting potencies in animal models, exceeded the TDI for di-n-butyl phthalate (DnBP) in several of the younger children.

• Response to the comment by M. Jensen et al.

  Authors: Jorma Toppari, Helena E Virtanen, Tina K Jensen, Katharina M Main, Niels E Skakkebaek

  Birth defects research. Part A, Clinical and molecular teratology. 02/2011; 91(2):127.

• Development: disorders of sex development-the tip of the iceberg?

  Authors: Anders Juul, Katharina M Main, Niels E Skakkebaek

  Nature reviews. Endocrinology. 01/2011; 7(9):504-5.

• OCT4 and downstream factors are expressed in human somatic urogenital epithelia and in culture of epididymal spheres.

  Authors: David M Kristensen, John E Nielsen, Mark Kalisz, Marlene D Dalgaard, Karine Audouze, Malene E Larsen, Grete K Jacobsen, Thomas Horn, Søren Brunak, Niels E Skakkebaek, Henrik Leffers

  Molecular human reproduction. 11/2010; 16(11):835-45.

  The transcription factor OCT4 plays a crucial role in the earliest differentiation of the mammalian embryo and in self-renewal of embryonic stem cells. However, it remains controversial whether thisThe transcription factor OCT4 plays a crucial role in the earliest differentiation of the mammalian embryo and in self-renewal of embryonic stem cells. However, it remains controversial whether this gene is also expressed in somatic tissues. Here, we use a combination of RT-PCR on whole and microdissected tissues, in situ hybridization, immunohistochemistry and western blotting to show that OCT4 and SOX2 together with downstream targets, UTF1 and REX1/ZFP42, are expressed in the human male urogenital tract. We further support these results by the analysis of DNA methylation of a region in the OCT4 promoter. In culture, human primary epididymal cells formed spheres that continued to express the investigated genes for at least 20 days. Transcriptomic analysis of cultured cells showed up-regulation of CD29, CD44 and CD133 that are normally associated with sphere-forming cancer stem cells. Furthermore, stimulation with retinoic acid resulted in down-regulation of OCT4 expression, however, without multilineage differentiation. Our results show that OCT4 and associated genes are expressed in somatic epithelial cells from the urogenital tract and that these cells can form spheres, a general marker of stem cell behaviour.

• Many putative endocrine disruptors inhibit prostaglandin synthesis.

  Authors: David M Kristensen, Maria L Skalkam, Karine Audouze, Laurianne Lesné, Christele Desdoits-Lethimonier, Hanne Frederiksen, Søren Brunak, Niels E Skakkebæk, Bernard Jégou, Jacob B Hansen, Steffen Junker, Henrik Leffers

  Environmental health perspectives. 11/2010; 119(4):534-41.

  Prostaglandins (PGs) play key roles in development and maintenance of homeostasis of the adult body. Despite these important roles, it remains unclear whether the PG pathway is a target for endocrineProstaglandins (PGs) play key roles in development and maintenance of homeostasis of the adult body. Despite these important roles, it remains unclear whether the PG pathway is a target for endocrine disruption. However, several known endocrine-disrupting compounds (EDCs) share a high degree of structural similarity with mild analgesics. Using cell-based transfection and transduction experiments, mass spectrometry, and organotypic assays together with molecular modeling, we investigated whether inhibition of the PG pathway by known EDCs could be a novel point of endocrine disruption. We found that many known EDCs inhibit the PG pathway in a mouse Sertoli cell line and in human primary mast cells. The EDCs also reduced PG synthesis in ex vivo rat testis, and this reduction was correlated with a reduced testosterone production. The inhibition of PG synthesis occurred without involvement of canonical PG receptors or the peroxisome proliferator-activated receptors (PPARs), which have previously been described as targets of EDCs. Instead, our results suggest that the compounds may bind directly into the active site of the cyclooxygenase (COX) enzymes, thereby obstructing the conversion of arachidonic acid to PG precursors without interfering with the expression of the COX enzymes. A common feature of the PG inhibitory EDCs is the presence of aromatic groups that may stabilize binding in the hydrophobic active site of the COX enzymes. Our findings suggest a hitherto unknown mode of action by EDCs through inhibition of the PG pathway and suggest new avenues to investigate effects of EDCs on reproductive and immunological disorders that have become increasingly common in recent decades.

• Cryptorchidism and hypospadias as a sign of testicular dysgenesis syndrome (TDS): environmental connection.

  Authors: Jorma Toppari, Helena E Virtanen, Katharina M Main, Niels E Skakkebaek

  Birth defects research. Part A, Clinical and molecular teratology. 10/2010; 88(10):910-9.

  Cryptorchidism and hypospadias are common genital birth defects that affect 2-9% and 0.2-1% of male newborns, respectively. The incidence of both defects shows large geographic variation, and inCryptorchidism and hypospadias are common genital birth defects that affect 2-9% and 0.2-1% of male newborns, respectively. The incidence of both defects shows large geographic variation, and in several countries increasing trends have been reported. The conditions share many risk factors, and they are also interlinked to the risk of testis cancer and poor semen quality. Testicular Dysgenesis Syndrome (TDS) may underlie many cases of all these male reproductive health problems. Genetic defects in androgen production or action can cause both cryptorchidism and hypospadias, but these are not common. A monogenic reason for cryptorchidism or hypospadias has been identified only in a small proportion of all cases. Environmental effects appear to play a major role in TDS. Exposure to several persistent chemicals has been found to be associated with the risk of cryptorchidism, and exposure to anti-androgenic phthalates has been shown to be associated with hormonal changes predisposing to male reproductive problems. Despite progress in identification of endocrine-disrupting substances, we are still far from knowing all the risk factors for these birth defects, and advice for prevention must be based on precautionary principles.

• Proceedings of the 5th Copenhagen Workshop on endocrine disrupters: ubiquitous endocrine disrupters and possible human health effects. Preface.

  Authors: Anna-Maria Andersson, Katrine Bay, Kenneth M Grigor, Jorma Toppari, Niels E Skakkebaek

  International journal of andrology. 04/2010; 33(2):251.

• Genital anomalies in boys and the environment.

  Authors: Katharina M Main, Niels E Skakkebaek, Helena E Virtanen, Jorma Toppari

  Best practice & research. Clinical endocrinology & metabolism. 04/2010; 24(2):279-89.

  The prevalence of male reproductive disorders, such as testicular cancer and impaired semen quality, is increasing in many, albeit not all, countries. These disorders are aetiologically linked withThe prevalence of male reproductive disorders, such as testicular cancer and impaired semen quality, is increasing in many, albeit not all, countries. These disorders are aetiologically linked with congenital cryptorchidism and hypospadias by common factors leading to perinatal disruption of normal testis differentiation, the testicular dysgenesis syndrome (TDS). There is recent evidence that also the prevalence of genital malformations is increasing and the rapid pace of increase suggests that lifestyle factors and exposure to environmental chemicals with endocrine disrupting properties may play a role. Recent prospective studies have established links between perinatal exposure to persistent halogenated compounds and cryptorchidism, as well as between phthalates and anti-androgenic effects in newborns. Maternal alcohol consumption, mild gestational diabetes and nicotine substitutes were also identified as potential risk factors for cryptorchidism. It may be the cocktail effect of many simultaneous exposures that result in adverse effects, especially during foetal life and infancy.

• Vitamin D receptor and vitamin D metabolizing enzymes are expressed in the human male reproductive tract.

  Authors: Martin Blomberg Jensen, John E Nielsen, Anne Jørgensen, Ewa Rajpert-De Meyts, David Møbjerg Kristensen, Niels Jørgensen, Niels E Skakkebaek, Anders Juul, Henrik Leffers

  Human reproduction (Oxford, England). 02/2010; 25(5):1303-11.

  The vitamin D receptor (VDR) is expressed in human testis, and vitamin D (VD) has been suggested to affect survival and function of mature spermatozoa. Indeed, VDR knockout mice and VD deficient ratsThe vitamin D receptor (VDR) is expressed in human testis, and vitamin D (VD) has been suggested to affect survival and function of mature spermatozoa. Indeed, VDR knockout mice and VD deficient rats show decreased sperm counts and low fertility. However, the cellular response to VD is complex, since it is not solely dependent on VDR expression, but also on cellular uptake of circulating VD and presence and activity of VD metabolizing enzymes. Expression of VD metabolizing enzymes has not previously been investigated in human testis and male reproductive tract. Therefore, we performed a comprehensive analysis of the expression of VDR, VD activating (CYP2R1, CYP27A1, CYP27B1) and inactivating (CYP24A1) enzymes in the testis, epididymis, seminal vesicle (SV), prostate and spermatozoa. Tissue samples were obtained after orchiectomy (testis n = 13; epididymis n = 7), prostatectomy (prostate n = 5 and SVs n = 3) and semen samples obtained after ejaculation (n = 13). mRNA was detected with RT-PCR and expression of proteins was determined by immunohistochemistry. VDR and VD metabolizing enzymes were concomitantly expressed in round and elongated spermatids, vesicles within the caput epididymis, and glandular epithelium of cauda epididymis, SV and prostate. The expression pattern in ejaculated spermatozoa varied, although, concomitant expression of VDR, CYP2R1, CYP27B1 and CYP24A1 was observed in neck and midpiece in a subpopulation of mature spermatozoa. On the basis of the marked expression of VDR and the VD metabolizing enzymes in human testis, ejaculatory tract and mature spermatozoa, we suggest that VD is important for spermatogenesis and maturation of human spermatozoa.

• Assessment of Circulating Sex Steroid Levels in Prepubertal and Pubertal Boys and Girls by a Novel Ultrasensitive Gas Chromatography-Tandem Mass Spectrometry Method.

  Authors: Frédérique Courant, Lise Aksglaede, Jean-Philippe Antignac, Fabrice Monteau, Kaspar Sorensen, Anna-Maria Andersson, Niels E Skakkebaek, Anders Juul, Bruno Le Bizec

  The Journal of clinical endocrinology and metabolism. 11/2009;

  Context: Estrogens and androgens play key roles for pubertal onset and sexual maturation. Most currently used immunoassays are not sensitive enough to accurately measure the low circulating levels ofContext: Estrogens and androgens play key roles for pubertal onset and sexual maturation. Most currently used immunoassays are not sensitive enough to accurately measure the low circulating levels of sex steroids in children without any signs of puberty. However, this does not exclude that sex steroids have important biological roles in prepubertal children. Objectives: To accurately determine levels of sex steroid hormones and their metabolites in serum of healthy children before any physical signs of puberty and to evaluate possible sex differences. Main Outcome Measures: Total (unconjugated plus conjugated) serum levels of 17beta-testosterone, 17alpha-testosterone, 5alpha-dihydrotestosterone, 5beta-dihydrotestosterone, androsterone, etiocholanolone, estradiol, and estrone measured by an ultrasensitive method based on gas chromatography-tandem mass spectrometry in samples from 81 healthy schoolchildren (42 boys) without any signs of puberty. For comparison, 48 pubertal children were studied. Results: 17beta-Estradiol levels in prepubertal boys were undetectable or extremely low (median < 3.7 pmol/liter), whereas levels in prepubertal girls were significantly higher (median 9.6 pmol/liter, P < 0.001). Among the older prepubertal children (>8 yr), girls had significantly higher androsterone (4.07 vs. 1.45 nmol/liter, P < 0.05), etiocholanolone (5.45 vs. 1.95 nmol/liter, P < 0.0001), 5alpha-dihydrotestosterone (0.11 vs. <0.10 nmol/liter, P < 0.01), and 17beta-testosterone concentrations (0.69 vs. 0.47 nmol/liter, P < 0.05) compared with similarly aged prepubertal boys. Conclusion: Using an accurate and sensitive method, we found significantly higher levels of estrogens as well as androgen metabolites in prepubertal girls compared with age-matched boys. The higher prepubertal sex steroid levels in girls may contribute to their earlier onset of puberty including pubic hair development.

• Analysis of gene expression profiles of microdissected cell populations indicates that testicular carcinoma in situ is an arrested gonocyte.

  Authors: Si Brask Sonne, Kristian Almstrup, Marlene Dalgaard, Agnieszka Sierakowska Juncker, Daniel Edsgard, Ludmila Ruban, Neil J Harrison, Christian Schwager, Amir Abdollahi, Peter E Huber, Søren Brunak, Lise Mette Gjerdrum, Harry D Moore, Peter W Andrews, Niels E Skakkebaek, Ewa Rajpert-De Meyts, Henrik Leffers

  Cancer research. 07/2009; 69(12):5241-50.

  Testicular germ cell cancers in young adult men derive from a precursor lesion called carcinoma in situ (CIS) of the testis. CIS cells were suggested to arise from primordial germ cells or gonocytes.Testicular germ cell cancers in young adult men derive from a precursor lesion called carcinoma in situ (CIS) of the testis. CIS cells were suggested to arise from primordial germ cells or gonocytes. However, direct studies on purified samples of CIS cells are lacking. To overcome this problem, we performed laser microdissection of CIS cells. Highly enriched cell populations were obtained and subjected to gene expression analysis. The expression profile of CIS cells was compared with microdissected gonocytes, oogonia, and cultured embryonic stem cells with and without genomic aberrations. Three samples of each tissue type were used for the analyses. Unique expression patterns for these developmentally very related cell types revealed that CIS cells were very similar to gonocytes because only five genes distinguished these two cell types. We did not find indications that CIS was derived from a meiotic cell, and the similarity to embryonic stem cells was modest compared with gonocytes. Thus, we provide new evidence that the molecular phenotype of CIS cells is similar to that of gonocytes. Our data are in line with the idea that CIS cells may be gonocytes that survived in the postnatal testis. We speculate that disturbed development of somatic cells in the fetal testis may play a role in allowing undifferentiated cells to survive in the postnatal testes. The further development of CIS into invasive germ cell tumors may depend on signals from their postpubertal niche of somatic cells, including hormones and growth factors from Leydig and Sertoli cells.

• Do perfluoroalkyl compounds impair human semen quality?

  Authors: Ulla Nordström Joensen, Rossana Bossi, Henrik Leffers, Allan Astrup Jensen, Niels E Skakkebaek, Niels Jørgensen

  Environmental health perspectives. 07/2009; 117(6):923-7.

  BACKGROUND: Perfluoroalkyl acids (PFAAs) are found globally in wildlife and humans and are suspected to act as endocrine disruptors. There are no previous reports of PFAA levels in adult men fromBACKGROUND: Perfluoroalkyl acids (PFAAs) are found globally in wildlife and humans and are suspected to act as endocrine disruptors. There are no previous reports of PFAA levels in adult men from Denmark or of a possible association between semen quality and PFAA exposure. OBJECTIVES: We investigated possible associations between PFAAs and testicular function. We hypothesized that higher PFAA levels would be associated with lower semen quality and lower testosterone levels. METHODS: We analyzed serum samples for levels of 10 different PFAAs and reproductive hormones and assessed semen quality in 105 Danish men from the general population (median age, 19 years). RESULTS: Considerable levels of perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), and perfluorohexane sulfonic acid were found in all young men (medians of 24.5, 4.9, and 6.6 ng/mL, respectively). Men with high combined levels of PFOS and PFOA had a median of 6.2 million normal spermatozoa in their ejaculate in contrast to 15.5 million among men with low PFOS-PFOA (p = 0.030). In addition, we found nonsignificant trends with regard to lower sperm concentration, lower total sperm counts, and altered pituitary-gonadal hormones among men with high PFOS-PFOA levels. CONCLUSION: High PFAA levels were associated with fewer normal sperm. Thus, high levels of PFAAs may contribute to the otherwise unexplained low semen quality often seen in young men. However, our findings need to be corroborated in larger studies.

• Is there a problem with male reproduction?

  Authors: Ulla Nordström Joensen, Niels E Skakkebaek, Niels Jørgensen

  Nature clinical practice. Endocrinology & metabolism. 04/2009; 5(3):144-5.

• Early puberty in internationally adopted girls: hormonal and clinical markers of puberty in 276 girls examined biannually over two years.

  Authors: Grete Teilmann, Jørgen H Petersen, Magdalena Gormsen, Karen Damgaard, Niels E Skakkebaek, Tina Kold Jensen

  Hormone research. 01/2009; 72(4):236-46.

  BACKGROUND AND AIMS: Retrospective studies have indicated that internationally adopted girls are at high risk of developing precocious puberty. Hypothetically, this could be due to selection bias.BACKGROUND AND AIMS: Retrospective studies have indicated that internationally adopted girls are at high risk of developing precocious puberty. Hypothetically, this could be due to selection bias. The aim of this study was to determine age at reaching pubertal milestones in healthy internationally adopted girls in a prospective, clinical study. METHODS: A longitudinal cohort study including 276 randomly recruited internationally adopted girls. At baseline, age ranged from 4 to 13 years. Participants were followed with biannual examinations over a period of 2 years. Examinations included height, weight, Tanner staging, blood sampling and bone age assessment. Age distribution at entering pubertal stages B2-B5 (breast development), PH1-PH5 (pubic hair development) and menarche was estimated by probit analysis. Data were compared to a reference population of Danish-born girls, studied cross-sectionally. RESULTS: Mean age at B2+ was 9.5 years (95% prediction interval 7.1-12.0 years) and mean age at menarche was 12.1 (10.2-14.0) years in adopted girls, which was significantly lower compared to the reference group (p < 0.0003). 16% of adopted girls entered stage B2 before 8 years of age. The puberty-related rise in LH, FSH and estradiol was detected at earlier ages in adopted girls compared to the reference group. CONCLUSION: Internationally adopted girls have a significantly higher risk of precocious pubertal maturation compared to Danish-born girls.