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Insulin-like growth factors in pygmies. The role of puberty in determining final stature
Insights
Short stature in pygmies is linked to lower insulin-like growth factor I (IGF I) levels during puberty. This suggests IGF I is crucial for pubertal growth acceleration, not testosterone alone.
Area of Science:
- Endocrinology
- Human Growth and Development
- Pediatrics
Background:
- Pygmies exhibit short stature, but their growth hormone levels are normal.
- Previous research indicated normal growth hormone in pygmy populations.
Purpose of the Study:
- To investigate the role of insulin-like growth factors (IGF I and II) and testosterone in the growth patterns of pygmies.
- To determine the precise factors contributing to the short stature observed in pygmy adults.
Main Methods:
- Serum concentrations of IGF I, IGF II, and testosterone were measured in pygmy and control children, adolescents, and adults.
- Linear growth and pubertal development (Tanner stage) were assessed and compared between groups.
Main Results:
- Prepubertal pygmy children showed no differences in growth or IGF levels compared to controls.
- Adolescent pygmies (boys and girls) had significantly lower serum IGF I concentrations than controls.
- Growth acceleration during puberty was observed in controls but was absent or blunted in pygmies.
Conclusions:
- The short stature of adult pygmies is primarily due to a lack of growth acceleration during puberty.
- Insulin-like growth factor I (IGF I) appears to be the principal mediator of normal pubertal growth.
- Testosterone does not significantly accelerate growth in the absence of elevated IGF I levels.
Abstract:
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.