Context: Adults with Klinefelter's syndrome (KS) are known to present disturbances of language skills and delayed learning abilities.

Objectives: To assess brain morphometry in KS and to correlate eventual volumetric changes with performance on neuropsychological tests.

Patients: 18 KS adults and 20 age-matched controls.

Methods: All participants underwent prospectively double spin echo brain magnetic resonance imaging (MRI) and neuropsychological testing of verbal and nonverbal domains. On the axial stack of MRI slices, regional brain volumes were measured either by automated segmentation (full brain, total cerebrospinal fluid, ventricular volume) or manual drawing with help of a neuroanatomy atlas (frontal, temporal and parietal lobes, gray matter component of the lobes, cerebellar hemispheres, hippocampal complexes).

Results: KS patients performed significantly lower than controls on language-related tasks exploring verbal processing speed and verbal executive function. They were diagnosed with significant enlargement of ventricular volume and bilateral reduction of cerebellar hemispheres. Furthermore, after separation of participants according to handedness and after correction of regional brain volumes for atrophy, a significant reduction of left temporal lobe volume was found in KS, compared with controls. Ventricular volume was inversely correlated with cognitive function, while left temporal lobe volume was positively correlated with language-related tasks.

Conclusion: This study hypothesizes that supernumerary X-chromosome and/or congenital hypogonadism provoke structural alterations in the subcortical pathways involved in language processing, thus providing a neurobiological substrate for cognitive deficits in KS.