The Effects of the X Chromosome on Intrinsic Functional Connectivity in the Human Brain: Evidence from Turner Syndrome Patients.

Turner syndrome (TS), a disorder caused by the congenital absence of one of the 2 X chromosomes in female humans, provides a valuable human "knockout model" for studying the functions of the X chromosome. At present, it remains unknown whether and how the loss of the X chromosome influences intrinsic functional connectivity (FC), a fundamental phenotype of the human brain. To address this, we performed resting-state functional magnetic resonance imaging and specific cognitive assessments on 22 TS patients and 17 age-matched control girls. A novel data-driven approach was applied to identify the disrupted patterns of intrinsic FC in TS. The TS girls exhibited significantly reduced whole-brain FC strength within the bilateral postcentral gyrus/intraparietal sulcus, angular gyrus, and cuneus and the right cerebellum. Furthermore, a specific functional subnetwork was identified in which the intrinsic FC between nodes was mostly reduced in TS patients. Particularly, this subnetwork is composed of 3 functional modules, and the disruption of intrinsic FC within one of these modules was associated with the deficits of TS patients in math-related cognition. Taken together, these findings provide novel insight into how the X chromosome affects the human brain and cognition, and emphasize an important role of X-linked genes in intrinsic neural coupling.