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A group of Babinga Pygmies from the Central African Republic have been analyzed for the acid phosphatase polymorphism with special reference to the ACPR allele. The frequency of this allele (17%) is one of the highest observed in Africa and is comparable only with those reported for the Khoikhoi and the San.
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Significant differences of taste thresholds for different sugars, salt, organic acids, and bitter products, observed in human populations in contrasted environments, are related to potential variations of traditional diet. In this respect, biochemical composition of the environment would be the major selective pressure for taste perception.
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Recent studies of African pygmies have concluded that the pattern of pygmy growth is similar to that of other Africans up to the time of puberty and that the short stature of adult pygmies is due primarily, if not solely, to the absence of accelerated adolescent growth. These conclusions are thought to be consistent with biochemical studies showing pygmies to have low levels of insulin-like growth factor 1 (IGF-1). All previous pygmy-growth studies have been of subjects of estimated, not known age. This paper reports the results of a mixed longitudinal growth study of Efe pygmy children of known age from birth to age 5 years. The mean adult stature of Efe pygmies is the shortest of any human population known, including other pygmy populations of central Africa. At birth, Efe were significantly smaller than neighbouring Lese Sudanic-speaking farmers and other rural Africans. During the first 5 years of life, Efe not only remained shorter than Lese controls at all ages, but the difference in stature between them increased. Unlike the Lese, Efe children showed a trend of increasingly negative z scores compared with the American reference population, from -2.71 (SD = 0.93) at 6 months to -4.16 (SD = 0.46) at age 5 years. These results indicate that suppression of pygmy growth does not occur solely at puberty, but from birth onward. Furthermore, they suggest that conclusions concerning the lack of an adolescent pygmy growth spurt have been premature and must await studies of older pygmy sub-adults of known age.
The hypothesis that Pygmies may differ from Caucasians in some aspects of the mechanics of locomotion was tested. A total of 13 Pygmies and 7 Caucasians were asked to walk and run on a treadmill at 4-12 km.h-1. Simultaneous metabolic measurements and three-dimensional motion analysis were performed allowing the energy expenditure and the mechanical external and internal work to be calculated. In Pygmies the metabolic energy cost was higher during walking at all speeds (P < 0.05), but tended to be lower during running (NS). The stride frequency and the internal mechanical work were higher for Pygmies at all walking (P < 0.05) and running (NS) speeds although the external mechanical work was similar. The total mechanical work for Pygmies was higher during walking (P < 0.05), but not during running and the efficiency of locomotion was similar in all subjects and speeds. The higher cost of walking in Pygmies is consistent with the allometric prediction for smaller subjects. The major determinants of the higher cost of walking was the difference in stride frequency (+9.45, SD 0.44% for Pygmies), which affected the mechanical internal work. This explains the observed higher total mechanical work of walking in Pygmies, even when the external component was the same. Most of the differences between Pygmies and Caucasians, observed during walking, tended to disappear when the speed was normalized as the Froude number. However, this was not the case for running. Thus, whereas the tested hypothesis must be rejected for walking, the data from running, do indeed suggest that Pygmies may differ in some aspects of the mechanics of locomotion.
Major metabolic effects of human growth hormone (HGH) were assessed in the African Babinga pygmy. Plasma free fatty acid (FFA) and glucose concentrations were measured in pygmies, HGH-deficient dwarfs, Bantu tribesmen, and Caucasian controls after each received 4 mg of HGH intravenously over a 20 min period. Pygmies had an early decrease of plasma FFA and glucose concentration, but did not exhibit a later lipolytic response. In neighboring Bantu tribesmen, American controls, and HGH-deficient dwarfs, both the early and late responses to intravenous HGH were present. The failure of plasma FFA concentration to increase in the pygmy after intravenous HGH was not due to a generalized defect in lipolysis since a normal lipolytic response was obtained with epinephrine (2 mug/min for 20 min).Pygmies, like HGH-deficient dwarfs, had significantly reduced insulin responses to both oral glucose and arginine. Insulin secretion was significantly reduced when compared with either Bantu tribesmen or American controls and was not altered by 2 wk of a high carbohydrate/high protein diet. HGH treatment in pygmies (5 mg b.i.d. for 5 days) failed to augment either glucose or arginine-induced insulin secretion. Glucagon consistently caused normal insulin secretion in HGH-deficient dwarfs and was, likewise, effective in each pygmy studied. In two offspring from different pygmy mothers and Bantu fathers, insulin responses to glucose were initially normal and increased in a normal manner after HGH treatment. In previous studies, HGH failed to reduce serum urea nitrogen concentration in pygmies. Sulfation factor was found to be normal. A consideration of the data in toto is consistent with a hypothesis that the metabolic findings in the pygmy may result from partial nonresponsiveness to either HGH or to a factor generated by HGH. This defect is not transmitted as either an autosomal or sex-linked dominant trait.
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.
We measured the serum concentrations of insulin-like growth factors (IGF) I and II and testosterone in pygmy children, adolescents, and adults, as well as in controls, to determine more precisely the role of these factors in controlling growth. We had previously shown that growth hormone levels were normal in pygmies. Prepubertal pygmy children and controls did not differ in linear growth or in serum concentrations of IGF I and II. In pygmy adolescent boys, the mean (+/- SEM) serum concentration of IGF I was only one third that in control adolescents, who were similar to the pygmies in age and Tanner stage of development (154 +/- 22 vs. 435 +/- 37 ng per milliliter; P less than 0.01). A similar difference in IGF I concentration was observed in girls (278 +/- 18 vs. 570 +/- 25 ng per milliliter; P less than 0.01). IGF II and testosterone levels were normal in all groups. There was a significant difference in growth between controls and pygmies only during puberty. There was a marked acceleration of growth in the controls during adolescence, but such an acceleration was absent or blunted in the pygmies. These findings suggest that the short stature of adult pygmies is due primarily to a failure of growth to accelerate during puberty. We postulate that IGF I is the principal factor responsible for normal pubertal growth and that testosterone does not accelerate growth appreciably in the absence of an increase in the level of IGF I.
The cause of growth hormone resistance and short stature in African Pygmies in unknown. Low levels of insulin-like growth factor 1 that fail to respond to growth hormone suggest a possible deficiency of growth hormone receptors. The high-affinity growth hormone-binding protein is a fragment of the growth hormone receptor and may be an indicator of the number of receptors in tissues. We measured growth hormone-binding activity in plasma from 20 pygmies and 12 control subjects (7 white Americans and 5 non-Pygmy black Africans of normal stature). Growth hormone binding to the high-affinity binding protein was significantly reduced in the Pygmies as compared with the controls (mean +/- SD, 6.50 +/- 2.33 percent vs. 12.95 +/- 3.95 percent bound per 160 microliters of plasma; P less than 0.001); however, there was substantial overlap between the values for Pygmies and controls. Growth hormone binding to the low-affinity binding protein was similar in Pygmies and control subjects. We conclude that Pygmies have low levels of high-affinity growth hormone-binding protein in their plasma, which may indicate a reduced number of growth hormone receptors in their tissues. The finding may help explain the resistance to growth in Pygmies, but there may be additional reasons, related to the receptors or not, for their short stature.
The Eastern Pygmies from Zaire and Western Pygmies from Cameroon, Congo, and the Central African Republic represent the two principal groups of African Pygmies. In the "recent divergence" hypothesis in which Western Pygmies are thought to be the result of hybridization between the ancestors of Eastern Pygmies and Bantu farmers who penetrated the equatorial belt and came into contact with Pygmies around 2-3 kiloyears ago. On the basis of recent archaeological research in the tropical rain forest, we propose a "pre-Bantu divergence" hypothesis, which posits the separation between the ancestors of Eastern and Western Pygmies earlier than 18 kiloyears ago. In order to test the two hypotheses, we analyzed the variation of the hypervariable region 1 of the mitochondrial DNA in the Mbenzele, Western Pygmies of the Central African Republic, and compared our results with those of previous mtDNA and Y chromosome studies. Distribution, sequence variation, and age of haplogroups along with genetic distances among populations, estimates of divergence times, and simulations based on the coalescent approach were found to be congruent with the pre-Bantu divergence but failed to support the recent divergence hypothesis.
Efe Pygmies of northeast Zaire have the shortest mean adult stature of any population on earth. Although various alterations in the GH/insulin-like growth factor I (IGF-I) axis have been suggested, the basis for short stature in the Pygmy is unknown. We previously described IGF-I unresponsiveness in a T lymphoblast cell line derived from an Efe Pygmy, and studies in five additional lines have confirmed severe IGF-I resistance in these cells. We have now performed experiments to determine the molecular basis for the IGF-I resistance in these cells. We found markedly decreased cell surface expression of IGF-I receptors with normal ligand binding affinity. The Pygmy IGF-I receptors were not autophosphorylated and did not transmit a signal in response to physiological concentrations of IGF-I. There was a substantially decreased level of IGF-I receptor messenger ribonucleic acid in the Pygmy cells with a normal messenger ribonucleic acid half-life. The nucleotide sequence of the full-length IGF receptor complementary DNA in Pygmy 1 showed no significant variation. These results indicate decreased IGF-I receptor gene transcription and IGF-I receptor signaling as the primary variation in the Pygmy cell lines. The findings point to the IGF-I receptor as the locus governing short stature in the African Pygmy and suggest that human stature may be genetically controlled by expression of the IGF-I receptor.