Background Inverse correlations have been reported between birth weight and
the Metabolic Syndrome (abdominal obesity, insulin resistance, hyperinsuli
nemia, glucose intolerance, dyslipidemia, and hypertension). These correlat
ions are thought to reflect primarily nutritional inadequacies during fetal
and early life. We explored familial influences on these correlations.
Methods Using birth weight data on 602 subjects from 65 pedigrees, we parti
tioned phenotypic correlations into familial and non-familial. The former a
re usually regarded as reflecting primarily genetic influences, although th
ey may also reflect environmental influences that are shared by family memb
ers, and the latter reflect random environmental influences.
Results A consistent pattern of positive familial and inverse non-familial
correlations were observed. The strongest familial correlations were betwee
n birth weight and fasting insulin (r=0.58, p=0.002), leptin (r=0.48, p=0.0
21), split proinsulin (r=0.51, p=0.090), and heart rate (r=0.39, p=0.037).
An inverse familial correlation was observed with HDL cholesterol (r=-0.28,
p=0.018). Non-familial correlations were weaker and only two subscapular-t
o-triceps skinfold ratio and fasting insulin - were statistically significa
nt.
Conclusion Since the familial and non-familial correlations were in opposit
e directions, we attribute the former to the pleiotropic effects of genes.
Specifically, we conclude that genes that increase birth weight also worsen
the Metabolic Syndrome in adult life. Since the inverse correlations repor
ted in the literature reflect mainly cohorts born in the early part of the
20th century, improved maternal nutrition since then may have allowed the e
xpression of genetic influences in our participants, all of whom were born
after 1950. Copyright (C) 2000 John Wiley & Sons, Ltd.