Habib Bouazzi, Soufiane Bouaziz, Mohammad Khalid Alwasiyah, Carlos Trujillo and Arnold Munnich
X-Linked Intellectual Disability (XLID) is an extremely heterogeneous disorder for which many of the causative genes are still unknown. So far, more than one hundred genes of the X chromosome have been found to alter in males manifesting intellectual disability. OGT (O-linked N-acetyl-Glucosamine-Transferase) gene is well known to be involved in endocrine alterations by the resistance of insulin in muscles and adipocytes and therefore the initiation of diabetes. It is reported to be involved also in cancer, brain development, and neurodegenerative diseases. However, its implication in chromosome X-Linked Intellectual Disability (XLID) has not been pinpointed up until now. In this study, we consider a family of three brothers having a non-syndromic intellectual disability and developmental delay while developing a genetic diagnosis. In the present study, clinical investigations, and medical exams were performed according to the French bioethics law. We performed X-exome sequencing in two patients. Sanger sequencing was accomplished to confirm novel mutations. X-chromosome inactivation was executed in the mother. Affected boys had a severe intellectual disability and mild dysmorphic features. The heterozygous mother had mild cognitive impairment. Her X-chromosome inactivation pattern was not skewed. We identified a novel missense mutation (c. 1193G>A) in the OGT gene. This mutation was inherited by the affected males, and it segregated with the abnormal phenotype. It was predicted to be damaging by SIFT (score 0). The mother was heterozygous and the only normal son was not mutated. The pathological phenotype of our patients might be linked to the new missense mutation, however, more similar clinical cases and functional studies are required to conclude the correlation between the genotype and the phenotype.
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