Identification of the Genomic Etiology of Unexplained Congenital Problems in Pediatric Patients: First Reported Case With Coffin-Siris Syndrome and Sialuria From India.

Coffin-Siris syndrome (CSS) (OMIM:614608) is a rare genetic disorder characterized by global developmental delay (GDD), speech impediment, coarse facial features, and hypoplastic or absent fifth fingernails/toenails. Genetic variants in the SMARCB1 gene are associated with CSS, benign tumors (schwannomas), and rhabdoid tumor predisposition syndrome. Genetic variants in the GNE gene are associated with the autosomal dominant sialuria (OMIM#269921), a rare inborn error of metabolism resulting in high levels of free sialic acid. Here we present case reports of two siblings: patient 1 (10 years) and patient 2 (2 years). While both siblings showed GDD and dysmorphic features such as hypotelorism and large ears, patient #1 exhibited additional phenotypes. Whole exome sequencing identified a heterozygous pathogenic variant, NM_003073.5:c.1096C>T (p.Arg366Cys), in the SMARCB1 gene in both siblings. In addition, patient 1 harbored a heterozygous likely pathogenic variant, NM_005476.7:c.2086G>A (p.Val696Met), in the GNE gene, which was absent in patient 2. The co-occurrence of the GNE variant may contribute to the increased severity of the phenotype in patient 1. This study is the first report worldwide of the co-occurrence of two extremely rare disorders. These findings highlight the complexity of genomic contributions while also emphasizing the value of genomic sequencing for congenital problems.