We implicated the X-chromosome THOC2 gene, which encodes largest subunit of the highly-conserved TREX (Transcription-Export) complex, in a clinically variable neurodevelopmental disorder with intellectual disability as the core phenotype. To study how compromised function of this essential eukaryotic gene leads to NDD outcomes, we generated a clinically-relevant mouse model based on a hypomorphic Thoc2 exon 37-38 deletion variant of a patient with ID, speech delay, hypotonia, and microcephaly. The Thoc2 exon 37-38 deletion male (Thoc2/Y) mice recapitulate the core phenotypes of THOC2 syndrome including smaller size and weight, and significant deficits in spatial learning, working memory and sensorimotor functions. The Thoc2/Y mouse brain development is significantly impacted by compromised THOC2/TREX function resulting in R-loop accumulation, DNA damage and consequent cell death. Overall, we suggest that perturbed R-loop homeostasis, in stem cells and/or differentiated cells in mice and the patient, and DNA damage-associated functional alterations are at the root of THOC2 syndrome.