A New Family with X-Linked Intellectual Disability 90: A Case Report of a Novel DLG3 Variant and Literature Review.

Introduction: X-linked intellectual disability (XLID) is a highly heterogeneous disease. Apart from Fragile X, other diseases that cause XLID are quite rare. The DLG3 gene variants cause XLID90.

Case presentation: This study presents 2 patients diagnosed with XLID90 after identifying a novel variant in the DLG3 gene through whole exome sequencing analysis. Both patients had autism spectrum disorder, intellectual disability, and dysmorphism. Additionally, an arachnoid cyst, which has not been previously reported in XLID90, was also detected in the patients. XLID90 has neither specific clinical findings nor dysmorphic features. Therefore, a detailed literature review is essential for clearly elucidating the phenotype. Here, one hundred and two XLID90 cases from 18 publications reporting pathogenic variants in the DLG3 gene were reviewed to investigate the detailed clinical findings among these patients. The literature review has shown that ID is more frequently observed in patients with truncating variants, while seizures are more commonly seen in patients with non-truncating variants.

Conclusion: This study will provide homogeneous healthcare to patients and allow for appropriate genetic counseling.