1984b; Nielsen and Wohlert, 1990; Ratcliffe, 1999]. An increased risk of pervasive developmental disorders in 47,XYY males has also been identified [Bender et al., 1984b; Ratcliffe et al., 1990; Nicolson et al., 1998]. The most common somatic phenotypic trait is increased size, beginning before puberty, and extending into a larger pubertal growth spurt. Evidence regarding head circumference is mixed, with some studies reporting no differences from controls despite the increase in height [Ratcliffe et al., 1994], and others an increased head circumference [Nicolson et al., 1998; Geerts et al., 2003].
