Specific learning disorders in sex chromosome aneuploidies: Neural circuits of literacy and mathematics

Sex chromosome aneuploidies (SCA) are associated with an increased risk for specific learning disorders (SLD). Individuals with Klinefelter Syndrome (KS) show an increased incidence of developmental dyslexia and individuals with Turner Syndrome (TS) are often affected by developmental dyscalculia. Accordingly, KS frequently coincides with verbal deficits, and TS with visual-spatial impairments. Though neurocognitive profiles of KS and TS are well-established, little is known about the neurobiology underling learning in SCA. This review summarizes current structural and functional magnetic resonance imaging (MRI) studies in KS and TS related to literacy and mathematical skills. It includes studies that focus on correlates between brain anatomy and cognition in SCA and on functional brain responses during learning-related tasks and at rest. We highlight important neural circuits that are related to domain-specific skills of literacy and mathematics. We discuss how identifying neuroendophenotypes of learning in SCA might contribute to developing a novel framework for SLD that accounts for potential genetic effects on learning, and from the X and Y chromosomes specifically. Future research directions are considered to establish clear brain-behavior relationships that might ultimately improve the treatment of SLD in SCA across development.