Glucose and Insulin Metabolism in Twins: Influence of Zygosity and Birth Weight

The Foetal Origins of Adult Disease: Interpreting the Evidence From Twin Studies

Twin studies have a contribution to make to the debate concerning the foetal origins of adult disease. Twins are growth retarded compared to singletons and experience post-natal catch-up growth. However, there is no evidence that twins are at increased risk of cardiovascular disease. Studying whether discordance in size at birth within monozygotic twin pairs is predictive of discordance in later life disease should help resolve whether the association between size at birth and later disease is due to common genetic factors. Results from studies of blood pressure in childhood and adult life looking at these within twin effects are far from conclusive. There are, however, methodological problems in the interpretation of these results, not least of which is the relatively small numbers of twin pairs studied. Studies exploring the effect of zygosity and chorion type on later disease provide may provide a useful extension of the research agenda. In summary, twin studies to date have raised more questions about the foetal origins hypothesis than they have resolved.

G/A polymorphism at -258 of the hepatic glucokinase promoter is not associated with decreased birth weight in preterm neonates

BACKGROUND

A high percentage of preterm neonates are born small for gestational age (SGA). These children show a high morbidity and mortality after birth and often develop insulin resistance with ensuing impaired glucose metabolism in adulthood. Since insulin is important for intrauterine growth, fetal insulin resistance might also influence birth weight of preterm neonates.

OBJECTIVES

A common polymorphism in the promoter region of the human hepatic glucokinase (-258) is associated with a decreased promoter activity, an enhanced insulin secretion, and hypertension and hepatic insulin resistance in adults. In this pilot study we wanted to investigate whether the G/A polymorphism at -258 of the hepatic glucokinase promoter has an effect on birth weight of preterm neonates and therefore might constitute a genotype leading to low birth weight and metabolic defects.

METHODS

We enrolled 106 preterm neonates in our study. 44 of them were SGA and 62 AGA neonates. We extracted DNA from a buccal swab and identified the polymorphism by PCR-ARMS.

RESULTS

We found no difference in the prevalence of the polymorphism in either groups.

CONCLUSION

The polymorphism at -258 of the fetal hepatic glucokinase promoter is most probably not of a major relevance in the pathophysiology of low birth weight in preterm neonates.

Low birth weight, nephron number, and kidney disease

More and more evidence is emerging that highlights the far-reaching consequences of prenatal (intrauterine) programming on organ function and adult disease. In humans, low birth weight (LBW) occurs more frequently in disadvantaged communities among whom there is often a disproportionately high incidence of adult cardiovascular disease, hypertension, diabetes mellitus, and kidney disease. Indeed, many epidemiologic studies have found an inverse association between LBW and higher blood pressures in infancy and childhood, and overt hypertension in adulthood. Multiple animal models have demonstrated the association of LBW with later hypertension, mediated, at least in part, by an associated congenital nephron deficit. Although no direct correlation has been shown between nephron number and birth weight in humans with hypertension, nephron numbers were found to be lower in adults with essential hypertension, and glomeruli tend to be larger in humans of lower birth weight. An increase in glomerular size is consistent with hyperfiltration necessitated by a reduction in total filtration surface area, which suggests a congenital nephron deficit. Hyperfiltration manifests clinically as microalbuminuria and accelerated loss of renal function, the prevalence of which are higher among adults who had been of LBW. A kidney with a reduced nephron number has less renal reserve to adapt to dietary excesses or to compensate for renal injury, as is highlighted in the setting of renal transplantation, where smaller kidney to recipient body-weight ratios are associated with poorer outcomes, independent of immunologic factors. Both hypertension and diabetes are leading causes of end-stage renal disease worldwide, and their incidences are increasing, especially in underdeveloped communities. Perinatal programming of these 2 diseases, as well as of nephron number, may therefore have a synergistic impact on the development of hypertension and kidney disease in later life. Existing evidence suggests that birth weight should be used as a surrogate marker for future risk of adult disease. Although the ideal solution to minimize morbidity would be to eradicate LBW, until this panacea is realized, it is imperative to raise awareness of its prognostic implications and to focus special attention toward early modification of risk factors for cardiovascular and renal disease in individuals of LBW.