Meier–Gorlin syndrome (MGS) is a rare genetic developmental disorder that causes primordial proportional dwarfism, microtia, absent or hypoplastic patellae and other skeletal anomalies. Overlapping skeletal symptoms make MGS difficult to diagnose clinically. We describe a 3-year-old boy with short stature, recurrent respiratory infections, short-rib dysplasia, tower head and facial dysmorphisms who was admitted to the Tomsk Genetic Clinic to verify a clinical diagnosis of Jeune syndrome. Clinical Exome sequencing revealed two variants (compound heterozygosity) in the ORC6 gene: c.2T>C(p.Met1Thr) and c.449+5G>A. In silico analysis showed the pathogenicity of these two mutations and predicted a decrease in donor splicing site strength for c.449+5G>A. An in vitro minigene assay demonstrated that variant c.449+5G>A causes a complete skipping of exon 4 in ORC6 gene. The parents asked for urgent prenatal testing for MGS for the next pregnancy, but it ended in a miscarriage. Thus, this case report may help to prevent MGS misdiagnosis in the future. We also performed in silico and functional analyses of ORC6 mutations and developed a restriction fragment length polymorphism and haplotype-based short-tandem-repeat assay for prenatal genetic testing for MGS. These findings should elucidate MGS aetiology and improve the quality of genetic counselling for affected families.

Defects in low-density lipoprotein receptor (LDLR) are associated with familial hypercholesterolemia (FH), manifested by atherosclerosis and cardiovascular disease. Defective LDLR in hepatocytes leads to increased blood cholesterol level that damage vascular cells, especially endothelial cells, through oxidative stress and inflammation. However, the distinctions between endothelial cells from individuals with normal and defective LDLR are not yet fully comprehended. In this study, we obtained and examined endothelial derivatives of induced pluripotent stem cells (iPSC) generated previously from conditionally healthy donors and compound heterozygous FH patients carrying pathogenic LDLR alleles. In normal iPSC-derived endothelial cells (iPSC-EC), we detected the LDLR protein predominantly in its mature form, while iPSC-EC from patients with FH display reduced level of mature LDLR and show abolished low-density lipoprotein uptake. RNA-seq of iPSC-EC with mutant LDLR revealed a unique transcriptome profile comprising downregulated genes related to monocarboxylic acid transport, exocytosis and cell adhesion, as well as upregulated signaling pathways of cell secretion and leukocyte activation. Overall, these findings suggest that LDLR defects increases susceptibility of endothelial cells to inflammation and oxidative stress. This, combined with elevated extrinsic cholesterol levels, may result in accelerated endothelial dysfunction, contributing to early progression of atherosclerosis and other cardiovascular pathologies related to FH.