scholarly journals The pathogenic p.(R391G) ABCC6 displays incomplete penetrance implying the necessity of an interacting partner for the development of pseudoxanthoma elasticum

2020 ◽  
Author(s):  
Flora Szeri ◽  
Agnes Miko ◽  
Nastassia Navasiolava ◽  
Ambrus Kaposi ◽  
Shana Verschuere ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Pseudoxanthoma Elasticum ◽  
Reference Population ◽  
Pathogenic Variant ◽  
Ectopic Calcification ◽  
Incomplete Penetrance ◽  
Sequence Variant ◽  
Primary Role ◽  
Inorganic Pyrophosphate ◽  
Pathogenic Variants

AbstractABCC6 encodes a transmembrane transporter playing a primary role in the efflux of ATP from hepatocytes to the bloodstream. ATP is then cleaved to AMP and inorganic pyrophosphate, a major inhibitor of ectopic calcification. Pathogenic variants of ABCC6 cause pseudoxanthoma elasticum, a multisystemic recessive ectopic calcification disease of variable severity. One of the mechanisms influencing the heterogeneity of a disorder is the penetrance of pathogenic variants. The penetrance of a sequence variant shows the proportion of individuals developing the expected phenotype in the presence of the variant. Incomplete penetrance indicates that the disease does not develop in all the cases when the pathogenic variant is present. Here, we investigated whether incomplete penetrance participates in the heterogeneity of pseudoxanthoma elasticum. By integrating the clinical and genetic data of 590 patients, we created the largest European pseudoxanthoma elasticum cohort. We identified two incomplete penetrant pathogenic variants, p.(V787I) and p.(R391G), based on their allele frequencies in our cohort and in the European reference population of gnomAD. The detailed characterization of the frequent p.(R391G) pathogenic variant suggested only 2% penetrance with an unaltered severity of the clinical phenotype. Based on our biochemical analysis, we hypothesize that the variant becomes deleterious only if an interacting partner is mutated simultaneously. These data point to new molecular mechanisms by revealing the potential existence of the first interacting partner of ABCC6. Our data are important for genetic counseling of pseudoxanthoma elasticum, suggesting a much lower disease heritability of these pathogenic variants.

scholarly journals ABCC6, Pyrophosphate and Ectopic Calcification: Therapeutic Solutions

2021 ◽  
Vol 22 (9) ◽  
pp. 4555
Author(s):  
Briana K. Shimada ◽  
Viola Pomozi ◽  
Janna Zoll ◽  
Sheree Kuo ◽  
Ludovic Martin ◽  
...  
Keyword(s):  
Soft Tissues ◽  
Genetic Disorders ◽  
Pseudoxanthoma Elasticum ◽  
Arterial Calcification ◽  
Ectopic Calcification ◽  
Direct Inhibition ◽  
Inorganic Pyrophosphate ◽  
Cardiovascular Tissues ◽  
Ectopic Mineralization

Pathological (ectopic) mineralization of soft tissues occurs during aging, in several common conditions such as diabetes, hypercholesterolemia, and renal failure and in certain genetic disorders. Pseudoxanthoma elasticum (PXE), a multi-organ disease affecting dermal, ocular, and cardiovascular tissues, is a model for ectopic mineralization disorders. ABCC6 dysfunction is the primary cause of PXE, but also some cases of generalized arterial calcification of infancy (GACI). ABCC6 deficiency in mice underlies an inducible dystrophic cardiac calcification phenotype (DCC). These calcification diseases are part of a spectrum of mineralization disorders that also includes Calcification of Joints and Arteries (CALJA). Since the identification of ABCC6 as the “PXE gene” and the development of several animal models (mice, rat, and zebrafish), there has been significant progress in our understanding of the molecular genetics, the clinical phenotypes, and pathogenesis of these diseases, which share similarities with more common conditions with abnormal calcification. ABCC6 facilitates the cellular efflux of ATP, which is rapidly converted into inorganic pyrophosphate (PPi) and adenosine by the ectonucleotidases NPP1 and CD73 (NT5E). PPi is a potent endogenous inhibitor of calcification, whereas adenosine indirectly contributes to calcification inhibition by suppressing the synthesis of tissue non-specific alkaline phosphatase (TNAP). At present, therapies only exist to alleviate symptoms for both PXE and GACI; however, extensive studies have resulted in several novel approaches to treating PXE and GACI. This review seeks to summarize the role of ABCC6 in ectopic calcification in PXE and other calcification disorders, and discuss therapeutic strategies targeting various proteins in the pathway (ABCC6, NPP1, and TNAP) and direct inhibition of calcification via supplementation by various compounds.

scholarly journals ABCC6 deficiency promotes dyslipidemia and atherosclerosis

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Christopher Brampton ◽  
Viola Pomozi ◽  
Li-Hsieh Chen ◽  
Ailea Apana ◽  
Sara McCurdy ◽  
...  
Keyword(s):  
Cholesterol Efflux ◽  
Molecular Mechanisms ◽  
Physiological Role ◽  
Hdl Cholesterol ◽  
Intima Media Thickness ◽  
Pseudoxanthoma Elasticum ◽  
Carotid Intima Media Thickness ◽  
Cholesterol Homeostasis ◽  
Plasma Lipoproteins ◽  
Ectopic Calcification

AbstractABCC6 deficiency promotes ectopic calcification; however, circumstantial evidence suggested that ABCC6 may also influence atherosclerosis. The present study addressed the role of ABCC6 in atherosclerosis using Ldlr−/− mice and pseudoxanthoma elasticum (PXE) patients. Mice lacking the Abcc6 and Ldlr genes were fed an atherogenic diet for 16 weeks before intimal calcification, aortic plaque formation and lipoprotein profile were evaluated. Cholesterol efflux and the expression of several inflammation, atherosclerosis and cholesterol homeostasis-related genes were also determined in murine liver and bone marrow-derived macrophages. Furthermore, we examined plasma lipoproteins, vascular calcification, carotid intima-media thickness and atherosclerosis in a cohort of PXE patients with ABCC6 mutations and compared results to dysmetabolic subjects with increased cardiovascular risk. We found that ABCC6 deficiency causes changes in lipoproteins, with decreased HDL cholesterol in both mice and humans, and induces atherosclerosis. However, we found that the absence of ABCC6 does not influence overall vascular mineralization induced with atherosclerosis. Decreased cholesterol efflux from macrophage cells and other molecular changes such as increased pro-inflammation seen in both humans and mice are likely contributors for the phenotype. However, it is likely that other cellular and/or molecular mechanisms are involved. Our study showed a novel physiological role for ABCC6, influencing plasma lipoproteins and atherosclerosis in a haploinsufficient manner, with significant penetrance.

scholarly journals Pathogenic variants in the AFG3L2 proteolytic domain cause SCA28 through haploinsufficiency and proteostatic stress-driven OMA1 activation

2019 ◽  
Vol 56 (8) ◽  
pp. 499-511 ◽  
Author(s):  
Susanna Tulli ◽  
Andrea Del Bondio ◽  
Valentina Baderna ◽  
Davide Mazza ◽  
Franca Codazzi ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Protein Quality ◽  
Mitochondrial Protein ◽  
Pathogenic Variant ◽  
Mitochondrial Fusion ◽  
Spinocerebellar Ataxia Type ◽  
Mitochondrial Morphology ◽  
Pathogenic Variants ◽  
Control Objective ◽  
Mitochondrial Calcium Uptake

BackgroundSpinocerebellar ataxia type 28 (SCA28) is a dominantly inherited neurodegenerative disease caused by pathogenic variants in AFG3L2. The AFG3L2 protein is a subunit of mitochondrial m-AAA complexes involved in protein quality control. Objective of this study was to determine the molecular mechanisms of SCA28, which has eluded characterisation to date.MethodsWe derived SCA28 patient fibroblasts carrying different pathogenic variants in the AFG3L2 proteolytic domain (missense: the newly identified p.F664S and p.M666T, p.G671R, p.Y689H and a truncating frameshift p.L556fs) and analysed multiple aspects of mitochondrial physiology. As reference of residual m-AAA activity, we included SPAX5 patient fibroblasts with homozygous p.Y616C pathogenic variant, AFG3L2+/− HEK293 T cells by CRISPR/Cas9-genome editing and Afg3l2−/− murine fibroblasts.ResultsWe found that SCA28 cells carrying missense changes have normal levels of assembled m-AAA complexes, while the cells with a truncating pathogenic variant had only half of this amount. We disclosed inefficient mitochondrial fusion in SCA28 cells caused by increased OPA1 processing operated by hyperactivated OMA1. Notably, we found altered mitochondrial proteostasis to be the trigger of OMA1 activation in SCA28 cells, with pharmacological attenuation of mitochondrial protein synthesis resulting in stabilised levels of OMA1 and OPA1 long forms, which rescued mitochondrial fusion efficiency. Secondary to altered mitochondrial morphology, mitochondrial calcium uptake resulted decreased in SCA28 cells.ConclusionOur data identify the earliest events in SCA28 pathogenesis and open new perspectives for therapy. By identifying similar mitochondrial phenotypes between SCA28 cells and AFG3L2+/− cells, our results support haploinsufficiency as the mechanism for the studied pathogenic variants.

scholarly journals The Role of MicroRNAs in Arrhythmogenic Cardiomyopathy: Biomarkers or Innocent Bystanders of Disease Progression?

2020 ◽  
Vol 21 (17) ◽  
pp. 6434
Author(s):  
Maria Bueno Marinas ◽  
Rudy Celeghin ◽  
Marco Cason ◽  
Gaetano Thiene ◽  
Cristina Basso ◽  
...  
Keyword(s):  
Gene Expression Regulation ◽  
Phenotypic Variability ◽  
Incomplete Penetrance ◽  
Primary Role ◽  
Arrhythmogenic Cardiomyopathy ◽  
Small Noncoding Rnas ◽  
Early Disease Detection ◽  
Pathogenic Variants ◽  
Fatty Replacement ◽  
Genes Encoding

Arrhythmogenic cardiomyopathy (AC) is an inherited cardiac disease characterized by a progressive fibro-fatty replacement of the working myocardium and by life-threatening arrhythmias and risk of sudden cardiac death. Pathogenic variants are identified in nearly 50% of affected patients mostly in genes encoding for desmosomal proteins. AC incomplete penetrance and phenotypic variability advocate that other factors than genetics may modulate the disease, such as microRNAs (miRNAs). MiRNAs are small noncoding RNAs with a primary role in gene expression regulation and network of cellular processes. The implication of miRNAs in AC pathogenesis and their role as biomarkers for early disease detection or differential diagnosis has been the objective of multiple studies employing diverse designs and methodologies to detect miRNAs and measure their expression levels. Here we summarize experiments, evidence, and flaws of the different studies and hitherto knowledge of the implication of miRNAs in AC pathogenesis and diagnosis.

scholarly journals Unsuspected somatic mosaicism for FBN1 gene contributes to Marfan syndrome

2021 ◽  
Author(s):  
Pauline Arnaud ◽  
Hélène Morel ◽  
Olivier Milleron ◽  
Laurent Gouya ◽  
Christine Francannet ◽  
...  
Keyword(s):  
Marfan Syndrome ◽  
Somatic Mosaicism ◽  
Variant Calling ◽  
Copy Number Variations ◽  
Pathogenic Variant ◽  
Single Nucleotide Variants ◽  
Bioinformatics Analyses ◽  
Single Nucleotide ◽  
Fbn1 Gene ◽  
Pathogenic Variants

Abstract Purpose Individuals with mosaic pathogenic variants in the FBN1 gene are mainly described in the course of familial screening. In the literature, almost all these mosaic individuals are asymptomatic. In this study, we report the experience of our team on more than 5,000 Marfan syndrome (MFS) probands. Methods Next-generation sequencing (NGS) capture technology allowed us to identify five cases of MFS probands who harbored a mosaic pathogenic variant in the FBN1 gene. Results These five sporadic mosaic probands displayed classical features usually seen in Marfan syndrome. Combined with the results of the literature, these rare findings concerned both single-nucleotide variants and copy-number variations. Conclusion This underestimated finding should not be overlooked in the molecular diagnosis of MFS patients and warrants an adaptation of the parameters used in bioinformatics analyses. The five present cases of symptomatic MFS probands harboring a mosaic FBN1 pathogenic variant reinforce the fact that apparently asymptomatic mosaic parents should have a complete clinical examination and a regular cardiovascular follow-up. We advise that individuals with a typical MFS for whom no single-nucleotide pathogenic variant or exon deletion/duplication was identified should be tested by NGS capture panel with an adapted variant calling analysis.

scholarly journals Disruption of Abcc6 Transporter in Zebrafish Causes Ocular Calcification and Cardiac Fibrosis

2020 ◽  
Vol 22 (1) ◽  
pp. 278
Author(s):  
Jianjian Sun ◽  
Peilu She ◽  
Xu Liu ◽  
Bangjun Gao ◽  
Daqin Jin ◽  
...  
Keyword(s):  
Vitamin K ◽  
Cardiac Fibrosis ◽  
Clinical Manifestations ◽  
Pseudoxanthoma Elasticum ◽  
Matrix Gla Protein ◽  
Ectopic Calcification ◽  
Transcription Activator ◽  
Multisystem Disorder ◽  
Ectopic Mineralization ◽  
Extensive Calcification

Pseudoxanthoma elasticum (PXE), caused by ABCC6/MRP6 mutation, is a heritable multisystem disorder in humans. The progressive clinical manifestations of PXE are accompanied by ectopic mineralization in various connective tissues. However, the pathomechanisms underlying the PXE multisystem disorder remains obscure, and effective treatment is currently available. In this study, we generated zebrafish abcc6a mutants using the transcription activator-like effector nuclease (TALEN) technique. In young adult zebrafish, abcc6a is expressed in the eyes, heart, intestine, and other tissues. abcc6a mutants exhibit extensive calcification in the ocular sclera and Bruch’s membrane, recapitulating part of the PXE manifestations. Mutations in abcc6a upregulate extracellular matrix (ECM) genes, leading to fibrotic heart with reduced cardiomyocyte number. We found that abcc6a mutation reduced levels of both vitamin K and pyrophosphate (PPi) in the serum and diverse tissues. Vitamin K administration increased the gamma-glutamyl carboxylated form of matrix gla protein (cMGP), alleviating ectopic calcification and fibrosis in vertebrae, eyes, and hearts. Our findings contribute to a comprehensive understanding of PXE pathophysiology from zebrafish models.

scholarly journals Quantitative Approach to Fragmented QRS in Arrhythmogenic Cardiomyopathy: From Disease towards Asymptomatic Carriers of Pathogenic Variants

2020 ◽  
Vol 9 (2) ◽  
pp. 545 ◽  
Author(s):  
Rob W. Roudijk ◽  
Laurens P. Bosman ◽  
Jeroen F. van der Heijden ◽  
Jacques M. T. de Bakker ◽  
Richard N. W. Hauer ◽  
...  
Keyword(s):  
Early Stage ◽  
Pathogenic Variant ◽  
Observer Agreement ◽  
Arrhythmogenic Cardiomyopathy ◽  
Fragmented Qrs ◽  
Early Disease Detection ◽  
Pathogenic Variants ◽  
Disease Penetrance ◽  
Ecg Leads ◽  
And Control

Fragmented QRS complexes (fQRS) are common in patients with arrhythmogenic cardiomyopathy (ACM). A new method of fQRS quantification may aid early disease detection in pathogenic variant carriers and assessment of prognosis in patients with early stage ACM. Patients with definite ACM (n = 221, 66%), carriers of a pathogenic ACM-associated variant without a definite ACM diagnosis (n = 57, 17%) and control subjects (n = 58, 17%) were included. Quantitative fQRS (Q-fQRS) was defined as the total amount of deflections in the QRS complex in all 12 electrocardiography (ECG) leads. Q-fQRS was scored by a single observer and reproducibility was determined by three independent observers. Q-fQRS count was feasible with acceptable intra- and inter-observer agreement. Q-fQRS count is significantly higher in patients with definite ACM (54 ± 15) and pathogenic variant carriers (55 ± 10) compared to controls (35 ± 5) (p < 0.001). In patients with ACM, Q-fQRS was not associated with sustained ventricular arrhythmia (p = 0.701) at baseline or during follow-up (p = 0.335). Both definite ACM patients and pathogenic variant carriers not fulfilling ACM diagnosis have a higher Q-fQRS than controls. This may indicate that increased Q-fQRS is an early sign of disease penetrance. In concealed and early stages of ACM the role of Q-fQRS for risk stratification is limited.

scholarly journals Pendred Syndrome in Two Galician Families: Insights into Clinical Phenotypes through Cellular, Genetic, and Molecular Studies

2008 ◽  
Vol 93 (1) ◽  
pp. 267-277 ◽  
Author(s):  
Fernando Palos ◽  
María E. R. García-Rendueles ◽  
David Araujo-Vilar ◽  
Maria Jesús Obregon ◽  
Rosa Maria Calvo ◽  
...  
Keyword(s):  
Outcome Measures ◽  
Molecular Mechanisms ◽  
Novel Mutation ◽  
Thyroid Tissue ◽  
Iodine Uptake ◽  
Incomplete Penetrance ◽  
Pendred Syndrome ◽  
Iodothyronine Deiodinase ◽  
Large Goiter ◽  
Iodine Retention

Abstract Context: We studied two families from Galicia (northwest Spain) with Pendred syndrome (PS) and unusual thyroid phenotypes. In family A, the proposita had a large goiter and hypothyroxinemia but normal TSH and free T3 (FT3). In family B, some affected members showed deafness but not goiter. Objective: Our objective was to identify the mutations causing PS and molecular mechanisms underlying the thyroid phenotypes. Interventions: Interventions included extraction of DNA and of thyroid tissue. Patients: Propositi and 10 members of the two families participated in the study. Main Outcome Measures: Main outcome measures included SLC26A4 gene analysis, deiodinase activities in thyroid tissue, and c.416–1G→A effects on SLC26A4 splicing. In addition, a primary PS thyrocyte culture, T-PS2, was obtained from propositus B and compared with another culture of normal human thyrocytes, NT, by Western blotting, confocal microscopy, and iodine uptake kinetics. Results: Proposita A was heterozygous for c.578C→T and c.279delT, presented with goiter, and had normal TSH and FT3 but low FT4 attributable to high type 1 and type 2 iodothyronine deiodinase activities in the goiter. Propositus B bore c.279delT and a novel mutation c.416–1G→A; some deaf relatives were homozygous for c.416–1G→A but did not present goiter. The c.279delT mutation was associated with identical haplotype in the two families. T-PS2 showed truncated pendrin retained intracellularly and high iodine uptake with low efflux leading to iodine retention. Conclusions: c.279delT is a founder mutation in Galicia. Proposita A adapted to poor organification by increasing deiodinase activities in the goiter, avoiding hypothyroidism. Lack of goiter in subjects homozygous for c.416–1G→A was due to incomplete penetrance allowing synthesis of some wild-type pendrin. Intracellular iodine retention, as seen in T-PS2, could play a role in thyroid alterations in PS.

scholarly journals Clinical and molecular characterization of patients fulfilling Chompret criteria for Li-Fraumeni syndrome in Southern Brazil

PLoS ONE ◽  
2021 ◽  
Vol 16 (9) ◽  
pp. e0251639
Author(s):  
Camila Matzenbacher Bittar ◽  
Yasminne Marinho de Araújo Rocha ◽  
Igor Araujo Vieira ◽  
Clévia Rosset ◽  
Tiago Finger Andreis ◽  
...  
Keyword(s):  
Soft Tissue Sarcomas ◽  
Pathogenic Variant ◽  
Southern Brazil ◽  
Premenopausal Breast Cancer ◽  
Li Fraumeni Syndrome ◽  
Cancer Predisposition Syndrome ◽  
Pathogenic Variants ◽  
Li Fraumeni ◽  
Group B ◽  
Adrenocortical Carcinomas

Li-Fraumeni syndrome (LFS) is an autosomal dominant cancer predisposition syndrome caused by pathogenic germline variants in the TP53 gene, characterized by a predisposition to the development of a broad spectrum of tumors at an early age. The core tumors related to LFS are bone and soft tissue sarcomas, premenopausal breast cancer, brain tumors, adrenocortical carcinomas (ACC), and leukemias. The revised Chompret criteria has been widely used to establish clinical suspicion and support TP53 germline variant testing and LFS diagnosis. Information on TP53 germline pathogenic variant (PV) prevalence when using Chompret criteria in South America and especially in Brazil is scarce. Therefore, the aim of this study was to characterize patients that fulfilled these specific criteria in southern Brazil, a region known for its high population frequency of a founder TP53 variant c.1010G>A (p.Arg337His), as known as R337H. TP53 germline testing of 191 cancer-affected and independent probands with LFS phenotype identified a heterozygous pathogenic/likely pathogenic variant in 26 (13.6%) probands, both in the DNA binding domain (group A) and in the oligomerization domain (group B) of the gene. Of the 26 carriers, 18 (69.23%) were R337H heterozygotes. Median age at diagnosis of the first tumor in groups A and B differed significantly in this cohort: 22 and 2 years, respectively (P = 0.009). The present study shows the clinical heterogeneity of LFS, highlights particularities of the R337H variant and underscores the need for larger collaborative studies to better define LFS prevalence, clinical spectrum and penetrance of different germline TP53 pathogenic variants.

scholarly journals A Novel Missense Variant in the Gene PPP2R5D Causes a Rare Neurodevelopmental Disorder with Increased Phenotype

2021 ◽  
Vol 2021 ◽  
pp. 1-7
Author(s):  
Lulu Yan ◽  
Ru Shen ◽  
Zongfu Cao ◽  
Chunxiao Han ◽  
Yuxin Zhang ◽  
...  
Keyword(s):  
De Novo ◽  
Genetic Disorder ◽  
Neurodevelopmental Disorder ◽  
Three Dimensional ◽  
Missense Variant ◽  
Pathogenic Variant ◽  
Dimensional Structure ◽  
Chinese Family ◽  
Speech Impairment ◽  
Pathogenic Variants

PPP2R5D-related neurodevelopmental disorder, which is mainly caused by de novo missense variants in the PPP2R5D gene, is a rare autosomal dominant genetic disorder with about 100 patients and a total of thirteen pathogenic variants known to exist globally so far. Here, we present a 24-month-old Chinese boy with developmental delay and other common clinical characteristics of PPP2R5D-related neurodevelopmental disorder including hypotonia, macrocephaly, intellectual disability, speech impairment, and behavioral abnormality. Trio-whole exome sequencing (WES) and Sanger sequencing were performed to identify the causal gene variant. The pathogenicity of the variant was evaluated using bioinformatics tools. We identified a novel pathogenic variant in the PPP2R5D gene (c.620G>T, p.Trp207Leu). The variant is located in the variant hotspot region of this gene and is predicted to cause PPP2R5D protein dysfunction due to an increase in local hydrophobicity and unstable three-dimensional structure. We report a novel pathogenic variant of PPP2R5D associated with PPP2R5D-related neurodevelopmental disorder from a Chinese family. Our findings expanded the phenotypic and mutational spectrum of PPP2R5D-related neurodevelopmental disorder.

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