Growth during puberty in the XYY boy.

The availability of a cohort of eight unselected XYY boys identified by newborn cytogenetic screening has enabled their growth to be studied longitudinally in comparison with controls from the same population. While no difference had been found in dimensions at birth, increased height velocity in childhood resulted in the XYY boys being 7.6 cm taller at the onset of their pubertal growth spurt. Increased intensity of growth at puberty with a peak height velocity of 10.6 cm/year contributed to their adult height of 188.1 cm. XYY boys showed twice the male-female difference in height implying that genes on the Y chromosome exert a quantitative effect on the sexual dimorphism of growth.