Growth analysis in clinical genetics.

The number of genetic and environmental determinants of human growth is very large and their interplay is responsible for the enormously complex phenomenon of prenatal and postnatal growth and simultaneous differentiation in function. Genetic factors participate substantially in determining size at birth, but become more and increasingly important in the realization of inherent potential after the age of two years. Thus, prenatal growth is determined by a greater number of environmental factors than postnatal growth, including parity, pregnancy spacing, maternal age, size, blood pressure, race, health, smoking, alcohol intake, twinning, intrauterine constraint, etc. Galilei's scale effect sets the upper limit of human size, and our surface area determines our metabolic rate and to some extent our life span. Age and rate of pubertal maturation varies with sex, race, and health of the individual, and may be dramatically influenced by numerous environmental and genetic disturbances. One of the most consistent and dramatic effects of autosomal aneuploidy on development is permanent reduction of growth rate, beginning very early in embryonic development. This effect on growth can be interpreted as an abnormality of developmental homeostasis or canalization. Reduced buffering or canalization of growth has been demonstrated in the DS and constitutes most elegant confirmation of the Waddington-Shapiro hypothesis; it ought to be demonstrable also in most if not all of the gonosomal aneuploidies. Thus, an ultrasonographic analysis of embryonic and fetal growth ought to be normal practice in all, not just high--risk pregnancies, and serve as valuable indicator of fetal developmental abnormality if IUGR is found. Because of difference in prognosis and possible difference in obstetric management, ultrasonographers ought to make a distinction in practice between (proportionate) IUGR and (disproportionate) CSOS. Depending on age of onset and severity, reduced prenatal movement can lead to the fetal akinesia sequence including growth retardation of all or part of the fetus. Neurohypotrophy shows that normal innervation is required for normal growth and function of limbs.