UNTIL recently specific behavioral deviations, other than mental deficiency, were not known to be associated with numerical chromosomal aberrations. The delineation of the "extra Y syndrome," however, has brought to the fore once more questions concerning observable genetic differences and their relationship to behavior.
The first XYY genotype was described in a 44-year-old man without physical abnormalities, whose psychological and behavioral characteristics were not recorded.1,2 By the time Balodimos et al3 reported their XYY karyotype, 11 other genotypes with an extra Y chromosome had already been published, giving rise to the statement that XYY males showed no consistent physical or mental stigmata, although the incidence of gonadal abnormalities was considered to be high. It was symptomatic of things to come that in this very paper an addendum was printed informing the readers that seven instances of the XYY karyotype had just been discovered among 197 mentally subnormal patients