Short stature and decreased serum growth hormone-binding protein in the Mountain Ok people of Papua New Guinea

Indirect evidence for the genetic determination of short stature in African Pygmies

Central African Pygmy populations are known to be the shortest human populations worldwide. Many evolutionary hypotheses have been proposed to explain this short stature: adaptation to food limitations, climate, forest density, or high mortality rates. However, such hypotheses are difficult to test given the lack of long-term surveys and demographic data. Whether the short stature observed nowadays in African Pygmy populations as compared to their Non-Pygmy neighbors is determined by genetic factors remains widely unknown. Here, we study a uniquely large new anthropometrical dataset comprising more than 1,000 individuals from 10 Central African Pygmy and neighboring Non-Pygmy populations, categorized as such based on cultural criteria rather than height. We show that climate, or forest density may not play a major role in the difference in adult stature between existing Pygmies and Non-Pygmies, without ruling out the hypothesis that such factors played an important evolutionary role in the past. Furthermore, we analyzed the relationship between stature and neutral genetic variation in a subset of 213 individuals and found that the Pygmy individuals' stature was significantly positively correlated with levels of genetic similarity with the Non-Pygmy gene-pool for both men and women. Overall, we show that a Pygmy individual exhibiting a high level of genetic admixture with the neighboring Non-Pygmies is likely to be taller. These results show for the first time that the major morphological difference in stature found between Central African Pygmy and Non-Pygmy populations is likely determined by genetic factors.

Altered growth patterns of a mountain Ok population of Papua New Guinea over 25 years of change

CONTEXT

The Mountain Ok (Mt Ok) people of Telefomin, who live at the interior of Papua New Guinea (PNG), were documented over 25 years ago to be one of the shortest populations on record, with average adult height below the fifth percentile (US). Serum Growth Hormone was detectable, Insulin-like Growth Factor-1 and serum indicators of protein nutritional status fell within the normal range, suggesting that these were not primary factors for their relative short stature.

OBJECTIVE

Since the Telefolmin people have experienced recent socioeconomic changes, they were re-evaluated in 2008, to examine height, weight, and body mass index (BMI), for insight into relative contributions of environment and other factors that modulate stature in children and adults.

STUDY DESIGN AND SETTING

Cross-sectional anthropometric data were collected from 474 individuals at Telefomin in 2008, and compared with anthropometric data from 342 individuals measured in 1983.

RESULTS

The height of Telefolmin subjects, below the fifth percentile in 1983, remained below the fifth percentile in 2008. Weight and BMI of peripubertal and adult age groups increased from 1983 to 2008. Male and female heights at peripubertal ages were significantly greater in 2008. Nevertheless, final adult height did not change significantly over the 25 years.

CONCLUSIONS

Recent socioeconomic changes appear to contribute to increased weight, BMI, and stature at younger ages in the Mt Ok at Telefomin. In contrast, unchanging adult stature may reflect a delay in the impact of socioeconomic changes, or genetic influences that modulate responsiveness to other growth regulators.

Diversity among African pygmies

Although dissimilarities in cranial and post-cranial morphology among African pygmies groups have been recognized, comparative studies on skull morphology usually pull all pygmies together assuming that morphological characters are similar among them and different with respect to other populations. The main aim of this study is to compare cranial morphology between African pygmies and non-pygmies populations from Equatorial Africa derived from both the Eastern and the Western regions in order to test if the greatest morphological difference is obtained in the comparison between pygmies and non-pygmies. Thirty three-dimensional (3D) landmarks registered with Microscribe in four cranial samples (Western and Eastern pygmies and non-pygmies) were obtained. Multivariate analysis (generalized Procrustes analysis, Mahalanobis distances, multivariate regression) and complementary dimensions of size were evaluated with ANOVA and post hoc LSD. Results suggest that important cranial shape differentiation does occur between pygmies and non-pygmies but also between Eastern and Western populations and that size changes and allometries do not affect similarly Eastern and Western pygmies. Therefore, our findings raise serious doubt about the fact to consider African pygmies as a homogenous group in studies on skull morphology. Differences in cranial morphology among pygmies would suggest differentiation after divergence. Although not directly related to skull differentiation, the diversity among pygmies would probably suggest that the process responsible for reduced stature occurred after the split of the ancestors of modern Eastern and Western pygmies.

Hormones and body size evolution in papionin primates

This study examines the evolution of size differences among papionin primates by measuring hormones that regulate size growth during ontogeny and influence ultimate adult size (insulin-like growth factor-I (IGF-I), insulin-like growth factor binding protein-3 (IGFBP-3), growth hormone binding protein (GHBP), dehydroepiandrosterone sulfate (DHEAS), testosterone, estradiol). The analyses assess longstanding ideas about circulating hormone levels and body size. Importantly, because the consensus papionin molecular phylogeny implies at least two episodes of size increase, this study offers opportunities to determine whether or not similar hormone profiles regulate this apparent evolutionary convergence (i.e., do larger-bodied papionins have higher levels of growth-related hormones than smaller-bodied papionins?). Five hundred and sixty serum samples (from 161 individuals) from 11 papionin species were analyzed using a two-level approach to address this issue. One used mixed longitudinal samples from two papionin species to test whether, during growth, large- and small-bodied species have higher and lower hormone levels, respectively. The second compared multiple papionin species to assess whether or not hormone levels covary with size in adult animals. Result show that size and hormone levels do not covary consistently across papionins, either during growth or in adulthood. Specifically, some smaller-bodied papionin species have higher absolute hormone levels than larger-bodied species. Differences in some hormone levels appear to track phylogeny more closely than body size. In contrast to studies based on single species, we demonstrate that, while the hormones analyzed affect growth, absolute circulating hormone levels either during growth or adulthood may be decoupled from interspecific differences in body size.

Physiology and pathophysiology of growth hormone-binding protein: methodological and clinical aspects

Circulating GH is partly bound to a high-affinity binding protein (GHBP), which in humans is derived from cleavage of the extracellular domain of the GH receptor. The precise biological function GHBP is unknown, although a regulation of GH bioactivity appears plausible. GHBP levels are determined by GH secretory status, body composition, age, and sex hormones, but the cause-effect relationships remain unclarified. In addition to the possible in vivo significance of GHBP, the interaction between GH and GHBP has methodological implications for both GH and GHBP assays. The present review concentrates on methodological aspects of GHBP measurements, GHBP levels in certain clinical conditions with a special emphasis on disturbances in the GH-IGF axis, and discusses the possible relationship between plasma GHBP and GH receptor status in peripheral tissues.

Growth hormone binding protein, insulin-like growth factor-I and short stature in two pygmy populations from the Philippines

The molecular basis and biochemical mediators of genetic growth propensity and adult height achievement in the general population are largely unknown. Pygmies represent one extreme of the height spectrum that may provide important clues regarding this issue. Previous studies in pygmies from Africa and Papua-New Guinea have shown decreased serum levels of growth hormone binding protein (GHBP), the circulating ectodomain of the growth hormone receptor (GHR). By inference, a similar limitation in tissue GHR expression has been assumed to be responsible for the partial growth hormone (GH) resistance observed in African pygmies. It is not clear how generalizable this concept is to other populations. To address this question, we studied two pygmy populations from the Philippines (Aeta and Mamanwa people) that are unrelated to the African pygmies. Serum GHBP and IGF-I levels were significantly decreased in both pygmy populations, compared to normal-statured Philippino controls. The results, together with previous observations in African and New Guinean pygmies, indicate that short stature is associated with low serum GHBP levels in pygmy populations of diverse origins and in different parts of the world. This strengthens the tentative postulate that the GHBP/GHR system plays an important role in the genetic and perhaps nutritional determination of adult stature in humans. Molecular genetic studies of the GHR gene in various pygmy populations may shed further light on the mystery of pygmy short stature.

Mitochondrial DNA variability of West New Guinea populations

This paper reports human mitochondrial DNA variability in West New Guinea (the least known, western side of the island of New Guinea), not yet described from a molecular perspective. The study was carried out on 202 subjects from 12 ethnic groups, belonging to six different Papuan language families, representative of both mountain and coastal plain areas. Mitochondrial DNA hypervariable region 1 (HVS 1) and the presence of the 9-bp deletion (intergenic region COII-tRNA(Lys)) were investigated. HVS 1 sequencing identified 73 polymorphic sites defining 89 haplotypes; the 9-bp deletion, which is considered a marker of Austronesian migration in the Pacific, was found to be absent in the whole West New Guinea study sample. Statistical analysis applied to the resulting haplotypes reveal high heterogeneity and an intersecting distribution of genetic variability in these populations, despite their cultural and geographic diversity. The results of subsequent phylogenetic approaches subdivide mtDNA diversity in West New Guinea into three main clusters (groups I-III), defined by sets of polymorphisms which are also shared by some individuals from Papua New Guinea. Comparisons with worldwide HVS 1 sequences stored in the MitBASE database show the absence of these patterns outside Oceania and a few Indonesian subjects, who also lack the 9-bp deletion. This finding, which is consistent with the effects of genetic drift and prolonged isolation of West New Guinea populations, lead us to regard these patterns as New Guinea population markers, which may harbor the genetic memory of the earliest human migrations to the island.

Initial characterization of the GH-IGF axis and nutritional status of the Ati Negritos of the Philippines

BACKGROUND AND OBJECTIVE

The Ati Negritos are a Pygmy-like aboriginal population from the Philippines with physical characteristics of short stature, dark skin and woolly, kinked hair. Their final height, components of their GH-IGF axis and various nutritional markers are described. SUBJECTS, DESIGN AND MEASUREMENTS: Auxological data and sera for the components of the GH-IGF axis and nutritional parameters were collected from 9 adult Ati Negritos in their native environment and 10 Filipinos in Sydney.

RESULTS

The height SDS (- 3.66 +/- 1.1 vs. - 1.01 +/- 1.2), weight SDS (- 2.30 +/- 1.6 vs. 0.10 +/- 0.7), and BMI SDS (- 1.4 +/- 1.8 vs. - 0.2 +/- 0.5) between the two groups were significantly different (P < 0.01). The mean height of the 6 male Ati Negritos was 149 +/- 7 and 144 +/- 3 cm for the females and are comparable with the African Pygmies and the Mountain Ok people of Papua New Guinea. The Ati Negritos showed lower growth hormone binding protein (GHBP), insulin-like growth factor I (IGF-I), insulin-like growth factor binding protein 3 (IGFBP-3), acid labile subunit (ALS), zinc, albumin, ferritin, iron, iron saturation and much higher insulin-like growth factor binding protein 2 (IGFBP-2) and plasma transferrin concentrations. No differences were noted in random growth hormone (GH), plasma insulin-like growth factor II (IGF-II), nor in their plasma concentrations of prealbumin, thyroid stimulating hormone (TSH) and free thyroxine (T4).

CONCLUSION

Perturbations of both the GH-IGF-I axis and nutritional markers exist in the Ati Negritos. These findings may be determinants of their stature; however, the aetiology of these changes remains to be fully elucidated.

Quantitative growth hormone secretion and final adult height

OBJECTIVE

The relationship of quantitative GH secretion to height, growth velocity and puberty is complex and has been the subject of extensive study in children. This study was designed to relate quantitative GH secretion to final height.

SUBJECTS

Twenty tall (> 183 cm, 90th centile for adult height) and 20 short (< 166 cm, 10th centile) postpubertal men who had recently completed linear growth (age range 18-27 years).

MEASUREMENTS

GH dynamics were studied on four occasions; insulin (0.15 units/kg, iv)-induced hypoglycaemia and GHRH (100 mg, iv) with and without the anticholinesterase, pyridostigmine (120 mg orally). Spontaneous nocturnal GH secretion was assessed by 20 minute sampling from 2100 h until 0600 h. GH was measured by IRMA. Analysis was by comparison of peak GH response and area under the curve (AUC). GH profiles were further analysed using the 'pulsar' programme.

RESULTS

The mean height in the tall group was 187.7 cm (range 183-197) compared to 163.5 cm (range 160-166) for the short group. No difference existed between groups in the GH response to hypoglycaemia or GHRH with and without pyridostigmine. Area under the curve, pulse number, length and amplitude for spontaneous nocturnal GH secretion showed no significant difference between the tall and short subjects. Serum IGF-I (mean 230.5 +/- 15. 4 vs. 230.6 +/- 18.9 microg/l) did not differ between the groups.

CONCLUSIONS

Quantitative GH secretion does not appear to be an important determinant of final height in healthy individuals.

Partial growth hormone insensitivity in childhood

There appears to be a continuum of GH-responsiveness, ranging from complete GH-resistance in Laron syndrome to normal GH-sensitivity. Partial GHI is suggested by findings at both ends of this spectrum; some patients with Laron-type dwarfism are less severely affected by their GHI than others (Savage et al, 1993; for a review, see Savage et al, 1995) and some short, non-GH-deficient, children have reduced responsiveness to GH. Among children with ISS, we have identified a subgroup where defects at the level of the GH receptor lead to a partial-GHI syndrome (Carlsson et al, 1994; Attie et al, 1995; Goddard et al, 1995). Partial-GHI may explain the growth failure in some children who do not meet the criteria for GHD. So far, the clinical evaluation of short children has been focused on the exclusion or demonstration of GHD. The diagnosis of GHD at present requires that stimulated or spontaneous GH concentrations should fail to reach a certain, arbitrarily determined level. This assumes that GH-sensitivity is equal in all subjects, with the exception of rare cases with Laron syndrome. The diagnosis of GHD is in itself controversial, and it has been suggested that GH testing should be supplemented by other measures such as auxological evaluation and measurement of other components of the GH/IGF-I axis (Rosenfeld et al, 1995). However, the fact that some short children have partial-GHI suggests that both GH secretion and GH responsiveness should be taken into consideration when investigating the cause of short stature (Figure 5). Many short children do not have GHD per se, but may be short due to inadequate GH stimulation because of reduced GH-sensitivity.

Serum growth hormone-binding protein is decreased in prepubertal children with idiopathic short stature

The causes for growth failure in children with idiopathic short stature (ISS) are not definitely established. Peripheral GH resistance due to changes at the level of the GH receptor has been suggested as one of the most probable explanation. In this study, we have selected a group of prepubertal children with ISS to evaluate the GHBP/receptor status by measuring the GH binding protein (GHBP) activity in plasma. Thirty prepubertal children with ISS (18 boys and 12 girls; age range: 4.79 to 11.33 yr) and twenty age-matched children with normal growth (11 boys and 9 girls) were studied. The ISS group presented growth retardation of -2.3 +/- 0.43 SD score (mean +/- SD) and normal GH secretion. Plasma IGF-I levels were below or in the low normal range (mean +/- SD: 136.3 +/- 62.3 micrograms/l, a concentration that was significantly different from IGF-I levels in the normal group (mean +/- SD: 187 +/- 57.5 micrograms/l p < 0.005). Plasma GHBP activity using a GH-binding/gel chromatography assay showed significantly lower values in ISS group (mean +/- SD: 7.17 +/- 1.5%) as compared with those of the control group (mean +/- SD: 12.02 +/- 2.04%; p < 0.001). There were no significant age- or sex-related differences in GHBP values in either group. The decreased GHBP levels observed in this group of children with ISS suggest that they may present a certain degree of GH insensitivity, probably due to a defect at the GH-receptor level.

Anthropometric characteristics and pulsatile growth hormone secretion patterns in premenopausal and postmenopausal women from Austria

The intercorrelations between 18 anthropometric variables, describing amount and distribution of subcutaneous fat tissue, and 12 growth hormone (GH) levels which had been obtained at intervals of 2 hours over a period of 24 hours, were tested in 25 premenopausal and 23 postmenopausal women from Austria. The 12 GH levels were included in the analyses because the GH shows typical pulsatile secretion patterns with peak values about midnight. Initially, premenopausal and postmenopausal women showed significantly different secretion patterns of GH; furthermore it became evident that the GH constantly correlated positively, however insignificantly, with stature height, but significantly negatively with all those measures describing amount and distribution of subcutaneous fat tissue. Beyond that the present paper indicates that age and menopausal status have a marked influence on GH secretion patterns. It became evident that, independent of menopausal status, typical association patterns between frequency of GH pulses per 24 hours, as well as the amplitude of the individual bursts and the amount of subcutaneous fat tissue, occur.

Influence of the high-affinity growth hormone (GH)-binding protein on plasma profiles of free and bound GH and on the apparent half-life of GH. Modeling analysis and clinical applications

The discovery of a specific high-affinity growth hormone (GH) binding protein (GH-BP) in plasma adds complexity to the dynamics of GH secretion and clearance. Intuitive predictions are that such a protein would damp sharp oscillations in GH concentrations otherwise caused by bursts of GH secretion into the blood volume, prolong the apparent half-life of circulating GH, and contribute a reservoir function. To test these implicit considerations, we formulated an explicit mathematical model of pulsatile GH secretion and clearance in the presence of absence of a specific high-affinity GH-BP. Simulation experiments revealed that the pulsatile mode of physiological GH secretion creates a highly dynamic (nonequilibrium) system, in which the half-life of free GH, its instantaneous secretion rate, and the GH-BP affinity and capacity all contribute to defining momentary levels of free, bound, and total GH, the percentage of GH bound to protein, and the percentage occupancy of GH-BP [corrected]. In contrast, the amount of free GH at equilibrium is specified only by the GH distribution volume and secretion rate and the half-life of free hormone. We conclude that the in vivo dynamics of GH secretion, trapping, and clearance from the circulation offer a variety of regulatory loci at which the time structure of free, bound, and total GH delivery to target tissues can be controlled physiologically.

Effect of growth hormone on the low level of growth hormone binding protein in idiopathic short stature

OBJECTIVE

Growth hormone receptor status was assessed in children with idiopathic short stature by evaluating plasma growth hormone-binding protein before and under GH therapy.

DESIGN

Among 22 children presenting idiopathic short stature, 15 were randomly selected to be treated with GH (1.2 IU/kg/week); they were studied before and under GH therapy. Untreated patients served as a control group for age and GH effect.

PATIENTS

Twenty-two prepubertal children, aged 5-11 years, were studied. They presented growth retardation of -2.8 +/- 0.1 SDS (mean +/- SEM). All had normal GH secretion and their mean IGF-I plasma level was normal.

MEASUREMENT

Growth hormone-binding protein was measured using high pressure liquid chromatography gel filtration. The specific binding of 125I-hGH to the growth hormone-binding protein was expressed as a percentage of the total radioactivity.

RESULTS

Specific binding of 125I-hGH to the high affinity growth hormone-binding protein was low with a mean +/- SEM value of 11.1 +/- 0.9% of radioactivity. In the treated group, growth hormone-binding protein increased significantly after 3 months of treatment; it reached 21.1 +/- 1.0% of radioactivity (mean +/- SEM) in the eight children who have been treated for 18 months. In the seven untreated children, the growth hormone-binding protein value increased to 16.2 +/- 1.1% after 18 months; this value is significantly lower than that found in the GH-treated children, demonstrating that the GH effect is greater than the age-related increase in the growth hormone-binding protein. A positive correlation was found between IGF-I plasma levels and growth hormone-binding protein and also between growth velocity and growth hormone-binding protein.

CONCLUSIONS

The low growth hormone-binding protein and the response to high doses of GH suggest partial GH resistance at the receptor level, in this group of children with idiopathic short stature.

Pseudohypopituitary syndromes

In a child with short stature, the finding of normal or elevated GH levels in the presence of low concentrations of IGF-I raises the following possibilities. (1) A modification of the GH molecule, which is still detected by RIA, but inactive biologically. Therefore, an RRA or bioassay for hGH should result in considerably lower GH measurements compared with RIA determinations in the same sample. As both bioassays as well as RRAs are not widely available and are hampered by several difficulties, few children with this presumptive diagnosis have been described. So far, it has not been possible to define a specific molecular defect in one of these patients. (2) Abnormalities of the GH receptor or postreceptor mechanisms lead to a GH insensitivity syndrome. Laron-type dwarfism is usually due to a deletion in the gene for hepatic GH receptors: the serum binding protein for GH is absent. In three additional populations, the Pygmies of Zaire, the little women of Loja in Ecuador and the Mountain Ok people in Papua New Guinea, alterations of GH receptor function have been described. Finally, some reports describe patients with normal or elevated serum levels of both growth hormone and IGF-I in whom resistance to IGF has been implied in the pathogenesis of small stature.