Corin and Left Atrial Cardiomyopathy, Hypertension, Arrhythmia, and Fibrosis.

Two siblings presented with cardiomyopathy, hypertension, arrhythmia, and fibrosis of the left atrium. Each had a homozygous null variant in CORIN, the gene encoding atrial natriuretic peptide (ANP)-converting enzyme. A plasma sample obtained from one of the siblings had no detectable levels of corin or N-terminal pro-ANP but had elevated levels of B-type natriuretic peptide (BNP) and one of the two protein markers of fibrosis that we tested. These and other findings support the hypothesis that BNP cannot fully compensate for a lack of activation of the ANP pathway and that corin is critical to normal ANP activity, left atrial function, and cardiovascular homeostasis.

A common benign intronic deletion masking a pathogenic deep intronic PCCB variant - genome sequencing and RNA studies to the rescue.

Propionic acidemia (PA) is an autosomal recessive metabolic disorder caused by variants in PCCA or PCCB, both sub-units of the propionyl-CoA carboxylase (PCC) enzyme. PCC is required for the catabolism of certain amino acids and odd-chain fatty acids. In its absence, the accumulated toxic metabolites cause metabolic acidosis, neurologic symptoms, multi-organ dysfunction and possible death. The clinical presentation of PA is highly variable, with typical onset in the neonatal or early infantile period. We encountered two families, whose children were diagnosed with PA. Exome sequencing (ES) failed to identify a pathogenic variant, and we proceeded with genome sequencing (GS), demonstrating homozygosity to a deep intronic PCCB variant. RNA analysis established that this variant creates a pseudoexon with a premature stop codon. The parents are variant carriers, though three of them display pseudo-homozygosity due to a common large benign intronic deletion on the second allele. The parental presumed homozygosity merits special attention, as it masked the causative variant at first, which was resolved only by RNA studies. Arriving at a rapid diagnosis, whether biochemical or genetic, can be crucial in directing lifesaving care, concluding the diagnostic odyssey, and allowing the family prenatal testing in subsequent pregnancies. This study demonstrates the power of integrative genetic studies in reaching a diagnosis, utilizing GS and RNA analysis to overcome ES limitations and define pathogenicity. Importantly, it highlights that intronic deletions should be taken into consideration when analyzing genomic data, so that pseudo-homozygosity would not be misinterpreted as true homozygosity, and pathogenic variants will not be mislabeled as benign.

Unique Ataxia-Oculomotor Apraxia 2 (AOA2) in Israel with Novel Variants, Atypical Late Presentation, and Possible Identification of a Poison Exon.

AOA2 is a rare progressive adolescent-onset disease characterised by cerebellar vermis atrophy, peripheral neuropathy and elevated serum alpha-fetoprotein (AFP) caused by pathogenic bi-allelic variants in SETX, encoding senataxin, involved in DNA repair and RNA maturation. Sanger sequencing of genomic DNA, co-segregation and oxidative stress functional studies were performed in Family 1. Trio whole-exome sequencing (WES), followed by SETX RNA and qRT-PCR analysis, were performed in Family 2. Sanger sequencing in Family 1 revealed two novel in-frame SETX deletion and duplication variants in trans (c.7009_7011del; p.Val2337del and c.7369_7371dup; p.His2457dup). Patients had increased induced chromosomal aberrations at baseline and following exposure to higher mitomycin-C concentration and increased sensitivity to oxidative stress at the lower mitomycin-C concentration in cell viability test. Trio WES in Family 2 revealed two novel SETX variants in trans, a nonsense variant (c.568C > T; p.Gln190*), and a deep intronic variant (c.5549-107A > G). Intronic variant analysis and SETX mRNA expression revealed activation of a cryptic exon introducing a premature stop codon (p.Met1850Lysfs*18) and resulting in aberrant splicing, as shown by qRT-PCR analysis, thus leading to higher levels of cryptic exon activation. Along with a second deleterious allele, this variant leads to low levels of SETX mRNA and disease manifestations. Our report expands the phenotypic spectrum of AOA2. Results provide initial support for the hypomorphic nature of the novel in-frame deletion and duplication variants in Family 1. Deep-intronic variant analysis of Family 2 variants potentially reveals a previously undescribed poison exon in the SETX gene, which may contribute to tailored therapy development.

Extracellular Vesicular Transmission of miR-423-5p from HepG2 Cells Inhibits the Differentiation of Hepatic Stellate Cells.

Liver fibrosis (LF) is a major cause of morbidity and mortality worldwide. Hepatic stellate cells (HSCs) are the primary source of extracellular matrix in the liver and their activation is a central event in LF development. Extracellular vesicles (EVs) are intercellular communication agents, which play important roles in physiological processes in chronic liver diseases. The aim of this study was to examine the crosstalk between hepatocytes and HSCs mediated by hepatocyte-secreted EVs. EVs were purified from primary mouse hepatocytes, HepG2 cell lines, under normal or stressed conditions. The effect of EVs on primary HSCs (pHSCs) differentiation was evaluated by measuring of differentiation markers. In addition, their impact on the carbon tetrachloride (CCl4)-induced fibrosis mouse model was evaluated. The results demonstrated that HepG2-EVs regulate HSC differentiation and that under stress conditions, promoted pHSCs differentiation into the myofibroblast phenotype. The evaluation of miRNA sequences in the HepG2 secreted EVs demonstrated high levels of miR-423-5p. The examination of EV cargo following stress conditions identified a significant reduction of miR-423-5p in HepG2-EVs relative to HepG2-EVs under normal conditions. In addition, pHSCs transfected with miR-423-5p mimic and exhibit lower mRNA levels of alpha smooth muscle actin and Collagen type 1 alpha, and the mRNA expression level of genes targeted the family with sequence-similarity-3 (FAM3) and Monoacylglycerol lipase (Mgll). This study strengthened the hypothesis that EVs are involved in LF and that their cargo changes in stress conditions. In addition, miR-423-5p was shown to be involved in HSCs differentiation and hence, fibrosis development.