Although prospective studies have shown that 47,XXX is also quite common (1/1,000 female births) [Nielsen and Wohlert, 1990; Ratcliffe, 1994], it is even more rarely recognized than 47,XXY, likely due to the mildness of the physical phenotypic characteristics. Similar to 47,XXY males, 47,XXX females also show increases in height beginning before puberty, and may have many of the same mild skeletal malformations such as clinodactyly and radio-ulnar synostosis. Behavioral characteristics commonly include increased risk for anxiety and impairment in executive function, such as impulsivity and difficulties with sustained attention and planning [Tennes et al., 1975]. The Denver prospective longitudinal study found that functional outcome in 47,XXX females was highly dependent on having strong social or familial support structures [Bender et al., 1999].
