NONO-related X-linked intellectual disability syndrome: Further clinical and molecular delineation.

The X-linked NONO gene encodes Non-Pou Domain-Containing Octamer-Binding Protein, a multifunctional member of the DBHS family involved in transcriptional regulation, RNA splicing and DNA repair. Pathogenic variants in NONO cause Intellectual Developmental Disorder, X-linked Syndromic (MIM #300967), characterised by intellectual disability, neurodevelopmental delay, cardiomyopathy, such as left ventricular non-compaction (LVNC), and congenital heart defects such as including atrial septal defect (ASD), ventricular septal defect (VSD), patent ductus arteriosus (PDA), and patent foramen ovale (PFO). This study reports three new patients with pathogenic hemizygous frameshift variants in NONO identified with exome sequencing, broadening the clinical presentation. The patients present with neurodevelopmental delay, macrocephaly, agenesis or hypoplasia of the corpus callosum and LVNC, confirming previous findings. These findings contribute to the understanding of the phenotypic diversity in patients with NONO pathogenic variants and highlight the need for further investigation of genotype-phenotype correlations, particularly with regard to early cardiac development, and prenatal presentations.