A Novel CCMS Model Reveals a Critical Intronic Sequence in the Snrpb Gene that is Required for Normal Development

Pathogenic variants in SNRPB, a common core spliceosomal factor, cause Cerebrocostomandibular Syndrome (CCMS). Most CCMS-associated variants result in increased inclusion of a PTC-containing alternative exon 2 (AE2). Using CRISPR/Cas9 we generated two mutant mice that carried a 46bp or a 61bp deletion upstream of Snrpb AE2. Mice and embryos carrying the 46bp deletion are normal. Whereas heterozygous and homozygous mutant embryos carrying the 61bp deletion (Δ61) exhibited smaller heads, micrognathia, malformations in the bones of the craniofacial region and ribs, and reduced survival, at low penetrance. Embryos homozygous for Δ61 showed a tendency towards increased inclusion of AE2 and reduced levels of Snrpb. In addition, this deletion increased the penetrance and severity of defects in Snrpbncc and Snrpbmes mutant embryos. Our findings indicate that this intronic region is important for SNRPB regulation in mice and should be investigated in CCMS patients that do not carry mutations in SNRPB coding exons.