Likely Pathogenic/Pathogenic Variants in the Spliceosome Complex Genes SNRNP200, SF3B1, SF3B2, and SF3B4 Implicated in Nonsyndromic Orofacial Cleft.

The genetic basis of nonsyndromic orofacial cleft (NsOFC) remains elusive, although associations have been identified with various genetic loci. NsOFC has a less pronounced genetic background than syndromic orofacial cleft (SyOFC), albeit Mendelian inheritance has been identified. Our hypothesis was that genes related to spliceosome function may contribute to NsOFC pathophysiology, as they do for some syndromic cases. Exome sequencing was conducted on 224 unrelated NsOFC probands. We performed filtering and analyses of predicted pathogenicity of rare variants using Highlander. We focused on 26 genes encoding spliceosome proteins. Subsequently, bioinformatic tools, such as AlphaFold, and PyMol, were applied to generate three-dimensional structures to interpret the effects of the identified variants on protein structure and interaction domains. We found six likely damaging variants: three heterozygous missense variants in small nuclear ribonucleoprotein U5 200 kDa subunit (SNRNP200) in three multiplex NsOFC families, and two missense and one splice site variant in splicing factor 3b subunit 1 (SF3B1), 4 (SF3B4), and 2 (SF3B2) in two posterior CP families and a complete CP patient, respectively. These results suggest that variants in the spliceosome complex genes, observed in 2.7% of NsOFC cases in our cohort, may contribute to disease susceptibility as potential risk factors.