Klinefelter syndrome: A neurodevelopmental disease of the synapse.

Klinefelter syndrome (KS; 47,XXY) is the most common sex chromosome disorder, affecting approximately 1 in every 500 to 650 newborn males. Children with KS display a spectrum of phenotypic manifestations, including abnormal neurocognitive phenotypes. However, due to the limited research focusing on the central nervous system, our understanding of the neurobiology of KS at the cellular and molecular levels remains largely unclear. In this study, we utilized cortical organoids derived from pluripotent stem cells and transcriptomic analysis to explore the mechanisms underlying early brain developmental defects in KS patients. We demonstrate that KS organoids display altered neurogenesis, gliogenesis, and glutamate signaling pathways. We believe these early alterations contribute to the abnormal brain development and later cognitive phenotypes in KS patients.