47,XYY is also not uncommon, estimated at 1/1,000 male births [Nielsen and Wohlert, 1990; Ratcliffe, 1994]. It was the object of intense interest in the 1970s, when studies appeared to find a higher number of individuals with 47,XYY in penal and psychiatric institutions than expected [Hook, 1973]. Although these studies were later recognized as having significant methodological flaws [Theilgaard, 1984; Gotz et al., 1999; Ike, 2000; [Weigmann, 2005], the idea that an additional Y chromosome will result in violent criminal behavior unfortunately continues to live on in popular perception [Ike, 2000]. 47,XYY does appear to be associated with an increased risk of behavioral and cognitive problems, including language and motor delay, disruptive behavior, impulsivity and poor attention, and impairment in social interaction, found in individuals diagnosed prenatally as well as those identified as part of postnatal evaluations [Bender et al., 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
