Project description:Matrix Gla protein (MGP) is a vitamin K-dependent post-translationally modified protein, highly expressed in vascular and cartilaginous tissues. It is a potent inhibitor of extracellular matrix mineralization. Biallelic loss of function variants in the MGP gene cause Keutel syndrome, an autosomal recessive disorder characterized by widespread calcification of various cartilaginous tissues and skeletal and vascular anomalies. In this study, we report four individuals from two unrelated families with two heterozygous variants in MGP, both altering the Cysteine 19 residue to phenylalanine or tyrosine. These individuals presented with a spondyloepiphyseal skeletal dysplasia characterized by short stature with a short trunk, diffuse platyspondyly, midface retrusion, progressive epiphyseal anomalies and brachytelephalangism. We investigated the cellular and molecular effects of one of the heterozygous deleterious variants (C19F) using both cell and genetically modified mouse models. Heterozygous ‘knock-in’ mice expressing C19F MGP recapitulated most of the skeletal anomalies observed in the affected individuals. We demonstrated that the main underlying mechanism leading to the observed skeletal dysplasia is endoplasmic reticulum stress-induced apoptosis of the growth plate chondrocytes. Our findings support that heterozygous variants in MGP altering Cys19 residue cause autosomal dominant spondyloepiphyseal dysplasia, a condition distinct from Keutel syndrome both clinically and molecularly.
Project description:Heterozygous pathogenic variants in POLR1A were identified as the cause of Acrofacial Dysostosis, Cincinnati-type in 2015. Craniofacial anomalies reminiscent of Treacher Collins syndrome were the predominant phenotype observed in the first 3 affected individuals. We have subsequently identified 17 additional individuals with 12 unique (11 novel) heterozygous variants in POLR1A and observed numerous additional phenotypes including developmental delay, infantile spasms, and structural cardiac defects. To understand the pathogenesis of this pleiotropy, we created an allelic series of POLR1A using a combination of in vivo (mouse) and in vitro models. We describe distinct spatiotemporal requirements for Polr1a during mouse embryogenesis and identify a requirement for Polr1a for survival of pre migratory and migratory neural crest cells, forebrain precursors, and the second heart field. We used CRISPR/Cas9 to recapitulate two human alleles in mouse, demonstrating pathogenicity of one and likely benign nature of the other. Our work greatly expands the phenotype of human POLR1A-related disorders, provides new evidence of reduced penetrance and variable expression of POLR1A heterozygous variants, and demonstrates a multi-faceted approach to characterize and define pathogenicity of variants.
Project description:Rare germline heterozygous missense variants of the BRCA1-Associated Protein 1 gene, BAP1, heterozygous missense variants cause a syndromic neurodevelopmental disorder
Project description:Lynch syndrome, caused by germline heterozygous mutations of the DNA mismatch repair genes MLH1, MSH2, MSH6 and PMS2, or deletions affecting the EPCAM gene upstream of MSH2, is characterized by a predisposition to early-onset colorectal and additional extracolonic cancers. An alternative but rare cause of Lynch syndrome is a constitutional epimutation of MLH1, which is characterized by promoter methylation and transcriptional silencing of a single allele in normal tissues. Worldwide, five families with autosomal dominant transmission of a constitutional MLH1 epimutation linked to an MLH1 haplotype with two single nucleotide variants (c.-27C>A and c.85G>T) have been identified. Array-based genotyping using Affymetrix SNP 6.0 data in four of these families revealed a shared haplotype extending across a ≤2.6 Mb region of chromosome 3p22 encompassing MLH1 and additional flanking genes, indicating common ancestry. Genomic DNA from 5 carriers of the c.-27C>A and c.85G>T variants was hybridized on Affymetrix SNP6.0 array according to manufacturer's procedures