DLG3 Impairment Caused by Missense Variants in Non-Syndromic X-Linked Mental Retardation

Abstract X-lined intellectual disability (XLID), formerly known as X-lined mental retardation, is defined as genetically heterogeneous disorders with remarkable cognitive impairment and abnormal adaptive behaviour skills. This study demonstrates the Disc-large homolog 3 (DLG3) gene impairment in 2 different unrelated male probands. The results detected two missense mutations in the DLG3 gene, c.2267 G > A (p.Arg756Gln) and c.2359G > A p. (Gly787Ser) using by NGS. Both mutations were run in the PolyPhen2 program for mutation sensitivity check and showed to have 0.709 and 1, respectively. The familial transmission pattern of MR detected both mothers to be heterozygote. The mutations were shown to have caused non-syndromic XLMR (NS-XLMR) as both males did not show any abnormal facial or physiological features. Based on the IQ measurement, proband 1 and 2’ IQs were measured 40 and 33, and they were diagnosed with moderate and severe XLMR, respectively. Both affected males showed significant deterioration in neural development and behaviour abilities, which indicates the significant impact of the mutation on neurotransmitters and maintenance of NMDA receptors in neural functions. However, further molecular and functional studies are necessary to provide more conclusive evidence of the detailed abnormalities caused by the reported mutations.