A comparative study of cognitive traits in human sex chromosome aneuploids and sterile and fertile euploids

Neurobehavioral phenotype of Klinefelter syndrome

A defined genetic syndrome with neurobehavioral components offers an unusual paradigm for the correlation of genetic defects with neurodevelopmental abnormalities. The power of the combination of detailed behavioral, neuroanatomical, and genetic studies has been demonstrated in studies of other conditions involving the sex chromosomes, such as Fragile X syndrome (Mazzocco [2000] Ment Retard Develop Disabil Res Rev. 6:96-106) and Turner syndrome (Ross [2000] Ment Retard Develop Disabil Res Rev. 6:135-141). Although the behavioral and neurologic difficulties that have been identified in Klinefelter syndrome (KS) are in most cases milder than the consequences of many other genetic syndromes, the deficits in KS cause significant morbidity, representing a more common, but poorly understood, subtype of those with learning disabilities. Both as children and as adults, KS subjects appear to offer a powerful genetic model for the study of language and language-based learning disabilities. Although it has been proposed that the language-based learning difficulties of KS boys are similar to those of nonaneuploidic dyslexics [Bender et al., 1986; Geschwind et al., 1998], this is not yet well established. The co-morbid frontal-executive dysfunction observed in KS is also a likely contributor to learning difficulties and, perhaps, social cognition, in many KS patients. It is also proposed that altered left-hemisphere functioning, whether causing, or due to, altered functional and anatomical cerebral dominance, is at the core of KS subjects' language problems. Although X chromosomal loci can provide only part of the picture, the study of KS subjects, a population with a relatively homogeneous etiology for dyslexia/dysphasia and frontal-executive dysfunction, offers many advantages over such a study in the general population, in which both dyslexia and attentional disorders are quite genetically heterogeneous [Decker and Bender, 1988; Pennington, 1990; Grigorenko et al., 1997; Geschwind et al., 1998]. Furthermore, the interaction of genetic factors and hormonal influences in the cognitive phenotypes described remains an unexplored area for future investigation. MRDD Research Reviews 2000;6:117-124.

Can spatial deficits in Turner's syndrome be explained by focal CNS dysfunction or atypical speech lateralization?

The spatial impairments of Turner's Syndrome were examined by administering perceptual, constructional, and nonverbal memory tasks to 11 probands and 22 controls matched for phenotypic sex, age, education, and hand preference. Visual imperception was more pronounced than constructional apraxia. Deficits in attention span were present, but they were not restricted to the visual modality or to nonverbal stimuli. Further neuropsychological tests of focal brain dysfunction and speech lateralization revealed slightly increased somatosensory thresholds of the left palm, attenuated manual asymmetry, and diminished right-visual-field superiority on letter identification. Different measures of spatial ability correlated with the somatosensory scores, the manual scores, and the speech representation scores, but the latter three variables showed no significant interrelationships. It is concluded that a unitary explanation in terms of focal CNS dysfunction or atypical speech representation can not account for the pattern of neuropsychological deficits seen in Turner's Syndrome.

Perceptual abnormalities in patients with chromatin negative gonadal dysgenesis and hypogonadotropic hypogonadism

The performance of 16 adult patients with chromatin negative gonadal dysgenesis was compared with that of normal men and women, and with patients with hypogonadotropic hypogonadism on a series of perceptual tasks chosen to assess speed and spatial abilities. The tasks included reaction time, embedded figures, rod and frame, size estimation, category width, broken figures, hidden figures, and incidental noticing. Male and female patients with hypogonadotropic hypogonadism and patients with 45,X showed significantly higher rod and frame scores than either normal males or females. Patients with 45,X also revealed higher set indexes on the reaction time test, narrower categories, and more difficulty with visual organization. Comparison with the hypogonadotropic hypogonadal patients suggested that perceptual speed seemed influenced more by genetic factors whereas visual spatial ability and the use of perceptual context appeared more related to hormonal factors.