Spatial Visualization, Aptitude For

Stafford (1961), using the identical blocks test as a measure of spatial visualization, studied 104 fathers and mothers and their 58 teenage sons and 70 daughters. Males showed higher average scores than females in both the parental and offspring group. No correlation of scores existed between fathers and mothers and none between fathers and sons. The correlations between fathers and daughters, between mothers and sons, and between mothers and daughters was what would be expected on the assumption that the aptitude for visualizing space is an X-linked recessive trait. Garron (1970) pointed out that if spatial and numerical abilities are determined by an X-linked recessive gene, patients with Turner syndrome should show superior not inferior performance. Bock and Kolakowski (1973) presented further evidence for X-linked recessive inheritance. Uncertainty about X-linkage was introduced by the studies of Loehlin et al. (1978). Sherman (1978) reviewed the whole subject of sex-related cognitive differences and discounted a biologic basis for them. Specifically, she examined the suggestion of X-linked inheritance of mathematical problem solving and spatial visualization and concluded that the hypotheses 'are disconfirmed.' Sherman (1978), 'in order to increase the precision of expression,' made use in her book of the neuter pronouns 'tey,' 'ter' and 'tem' when the sex of the person was used in a generic sense. The three neologisms were conceived as the singular equivalents of they, their and them.

Smalley et al. (1989) examined performance on 6 spatial tests in 73 members of 4 generations of an extended kindred. Nonadditive genetic variance was substantial for 1 of the 6 tests, card rotations. Whether this nonadditive genetic variance was due to a major autosomal gene was equivocal in light of results from segregation and linkage analyses. There was no evidence for the genetic variance for mental rotations or hidden patterns, in contrast to previous findings suggesting major gene involvement (Ashton et al., 1979). Smalley et al. (1989) concluded that if spatial ability is due, in part, to an autosomal major gene, the gene has variable expression (reflected in different tests) or genetic heterogeneity is pronounced. The rationale for studying a single large kindred was the possibility of reducing genetic heterogeneity and increasing the power of linkage studies.

Turner syndrome (monosomy X) is associated with a characteristic neurocognitive profile that includes impaired visuospatial/perceptual abilities. Ross et al. (2000) used a molecular approach to identify a critical region of the X chromosome for neurocognitive aspects of Turner syndrome. Partial deletions of Xp in 34 females were mapped by FISH or by loss of heterozygosity of polymorphic markers. Discriminant function analysis optimally identified the Turner syndrome-associated neurocognitive phenotype. Only subjects missing approximately 10 Mb of distal Xp manifested the specified neurocognitive profile. The phenotype was seen with either paternally or maternally inherited deletions and with either complete or incomplete skewing of X inactivation. Fine mapping of informative deletions implicated a critical region of less than 2 Mb within the pseudoautosomal region (PAR1). Ross et al. (2000) concluded that the haploinsufficiency of a PAR1 gene or genes is the basis for susceptibility to the Turner syndrome neurocognitive phenotype. Females with nonmosaic deletions missing only distal Xp22.33, at a minimum, manifested the defined Turner syndrome-associated cognitive profile.