Cognition and the Sex Chromosomes: Studies in Turner Syndrome

Turner syndrome (TS) is a human genetic disorder involving females who lack all or part of one X chromosome. The complex phenotype includes ovarian failure, a characteristic neurocognitive profi le and typical physical features. TS features are associated not only with complete monosomy X but also with partial deletions of either the short (Xp) or long (Xq) arm (partial monosomy X). Impaired visual-spatial/perceptual abilities are characteristic of TS children and adults of varying races and socioeconomic status, but global developmental delay is uncommon. The cognitive phenotype generally includes normal verbal function with relatively impaired visual-spatial ability, attention, working memory, and spatially dependent executive function. The constellation of neurocognitive defi cits observed in TS is most likely multifactorial and related to a complex interaction between genetic abnormalities and hormonal defi ciencies. Furthermore, other determinants, including an additional genetic mechanism, imprinting, may also contribute to cognitive defi cits associated with monosomy X. As a relatively common genetic disorder with well-defi ned manifestations, TS presents an opportunity to in