Histiocytoid cardiomyopathy and microphthalmia with linear skin defects syndrome: phenotypes linked by truncating variants in NDUFB11

Variants in NDUFB11, which encodes a structural component of complex I of the mitochondrial respiratory chain (MRC), were recently independently reported to cause histiocytoid cardiomyopathy (histiocytoid CM) and microphthalmia with linear skin defects syndrome (MLS syndrome). Here we report an additional case of histiocytoid CM, which carries a de novo nonsense variant in NDUFB11 (ENST00000276062.8: c.262C > T; p.[Arg88*]) identified using whole-exome sequencing (WES) of a family trio. An identical variant has been previously reported in association with MLS syndrome. The case we describe here lacked the diagnostic features of MLS syndrome, but a detailed clinical comparison of the two cases revealed significant phenotypic overlap. Heterozygous variants in HCCS (which encodes an important mitochondrially targeted protein) and COX7B, which, like NDUFB11, encodes a protein of the MRC, have also previously been identified in MLS syndrome including a case with features of both MLS syndrome and histiocytoid CM. However, a systematic review of WES data from previously published histiocytoid CM cases, alongside four additional cases presented here for the first time, did not identify any variants in these genes. We conclude that NDUFB11 variants play a role in the pathogenesis of both histiocytoid CM and MLS and that these disorders are allelic (genetically related)

Ethnicity, consanguinity, and genetic architecture of hypertrophic cardiomyopathy

AIMS: Hypertrophic cardiomyopathy (HCM) is characterized by phenotypic heterogeneity that is partly explained by the diversity of genetic variants contributing to disease. Accurate interpretation of these variants constitutes a major challenge for diagnosis and implementing precision medicine, especially in understudied populations. The aim is to define the genetic architecture of HCM in North African cohorts with high consanguinity using ancestry-matched cases and controls. METHODS AND RESULTS: Prospective Egyptian patients (n = 514) and controls (n = 400) underwent clinical phenotyping and genetic testing. Rare variants in 13 validated HCM genes were classified according to standard clinical guidelines and compared with a prospective HCM cohort of majority European ancestry (n = 684). A higher prevalence of homozygous variants was observed in Egyptian patients (4.1% vs. 0.1%, P = 2 × 10-7), with variants in the minor HCM genes MYL2, MYL3, and CSRP3 more likely to present in homozygosity than the major genes, suggesting these variants are less penetrant in heterozygosity. Biallelic variants in the recessive HCM gene TRIM63 were detected in 2.1% of patients (five-fold greater than European patients), highlighting the importance of recessive inheritance in consanguineous populations. Finally, rare variants in Egyptian HCM patients were less likely to be classified as (likely) pathogenic compared with Europeans (40.8% vs. 61.6%, P = 1.6 × 10-5) due to the underrepresentation of Middle Eastern populations in current reference resources. This proportion increased to 53.3% after incorporating methods that leverage new ancestry-matched controls presented here. CONCLUSION: Studying consanguineous populations reveals novel insights with relevance to genetic testing and our understanding of the genetic architecture of HCM

Widespread translational control of fibrosis in the human heart by RNA-binding proteins

BACKGROUND: Fibrosis is a common pathology in many cardiac disorders and is driven by the activation of resident fibroblasts. The global post-transcriptional mechanisms underlying fibroblast-to-myofibroblast conversion in the heart have not been explored. METHODS: Genome-wide changes of RNA transcription and translation during human cardiac fibroblast activation were monitored with RNA sequencing and ribosome profiling. We then used an RNA-binding protein-based analyses to identify translational regulators of fibrogenic genes. The integration with cardiac ribosome occupancy levels of 30 dilated cardiomyopathy patients demonstrates that these post-transcriptional mechanisms are also active in the diseased fibrotic human heart. RESULTS: We generated nucleotide-resolution translatome data during the TGFβ1-driven cellular transition of human cardiac fibroblasts to myofibroblasts. This identified dynamic changes of RNA transcription and translation at several time points during the fibrotic response, revealing transient and early-responder genes. Remarkably, about one-third of all changes in gene expression in activated fibroblasts are subject to translational regulation and dynamic variation in ribosome occupancy affects protein abundance independent of RNA levels. Targets of RNA-binding proteins were strongly enriched in post-transcriptionally regulated genes, suggesting genes such as MBNL2 can act as translational activators or repressors. Ribosome occupancy in the hearts of patients with dilated cardiomyopathy suggested the same post-transcriptional regulatory network was underlying cardiac fibrosis. Key network hubs include RNA-binding proteins such as PUM2 and QKI that work in concert to regulate the translation of target transcripts in human diseased hearts. Furthermore, silencing of both PUM2 and QKI inhibits the transition of fibroblasts toward pro-fibrotic myofibroblasts in response to TGFβ1. CONCLUSIONS: We reveal widespread translational effects of TGFβ1 and define novel post-transcriptional regulatory networks that control the fibroblast-to-myofibroblast transition. These networks are active in human heart disease and silencing of hub genes limits fibroblast activation. Our findings show the central importance of translational control in fibrosis and highlight novel pathogenic mechanisms in heart failure

HIV Evolution in Early Infection: Selection Pressures, Patterns of Insertion and Deletion, and the Impact of APOBEC

The pattern of viral diversification in newly infected individuals provides information about the host environment and immune responses typically experienced by the newly transmitted virus. For example, sites that tend to evolve rapidly across multiple early-infection patients could be involved in enabling escape from common early immune responses, could represent adaptation for rapid growth in a newly infected host, or could represent reversion from less fit forms of the virus that were selected for immune escape in previous hosts. Here we investigated the diversification of HIV-1 env coding sequences in 81 very early B subtype infections previously shown to have resulted from transmission or expansion of single viruses (n = 78) or two closely related viruses (n = 3). In these cases, the sequence of the infecting virus can be estimated accurately, enabling inference of both the direction of substitutions as well as distinction between insertion and deletion events. By integrating information across multiple acutely infected hosts, we find evidence of adaptive evolution of HIV-1 env and identify a subset of codon sites that diversified more rapidly than can be explained by a model of neutral evolution. Of 24 such rapidly diversifying sites, 14 were either i) clustered and embedded in CTL epitopes that were verified experimentally or predicted based on the individual's HLA or ii) in a nucleotide context indicative of APOBEC-mediated G-to-A substitutions, despite having excluded heavily hypermutated sequences prior to the analysis. In several cases, a rapidly evolving site was embedded both in an APOBEC motif and in a CTL epitope, suggesting that APOBEC may facilitate early immune escape. Ten rapidly diversifying sites could not be explained by CTL escape or APOBEC hypermutation, including the most frequently mutated site, in the fusion peptide of gp41. We also examined the distribution, extent, and sequence context of insertions and deletions, and we provide evidence that the length variation seen in hypervariable loop regions of the envelope glycoprotein is a consequence of selection and not of mutational hotspots. Our results provide a detailed view of the process of diversification of HIV-1 following transmission, highlighting the role of CTL escape and hypermutation in shaping viral evolution during the establishment of new infections

Role and possible mechanisms of clenbuterol in enhancing reverse remodelling during mechanical unloading in murine heart failure

Aims Combined left ventricular assist device (LVAD) and pharmacological therapy has been proposed to favour myocardial recovery in patients with end-stage heart failure (HF). Clenbuterol (Clen), a β2-adrenoceptor (β2-AR) agonist, has been used as a part of this strategy. In this study, we investigated the direct effects of clenbuterol on unloaded myocardium in HF. Methods and results Left coronary artery ligation or sham operation was performed in male Lewis rats. After 4–6 weeks, heterotopic abdominal transplantation of the failing hearts into normal recipients was performed to induce LV unloading (UN). Recipient rats were treated with saline (Sal) or clenbuterol (2 mg/kg/day) via osmotic minipumps (HF + UN + Sal or HF + UN + Clen) for 7 days. Non-transplanted HF animals were treated with Sal (Sham + Sal, HF + Sal) or clenbuterol (HF + Clen). LV myocytes were isolated and studied using optical, fluorescence, and electrophysiological techniques. Clenbuterol treatment improved in vivo LV function measured with echocardiography (LVEF (%): HF 35.9 ± 2 [16], HF + Clen 52.1 ± 1.4 [16]; P < 0.001; mean ± SEM [n]). In combination with unloading, clenbuterol increased sarcomere shortening (amplitude (µm): HF + UN + Clen 0.1 ± 0.01 [50], HF + UN + Sal 0.07 ± 0.01 [38]; P < 0.001) by normalizing the depressed myofilament sensitivity to Ca2+ (slope of the linear relationship between Ca2+ transient and sarcomere shortening hysteresis loop during relaxation (μm/ratio unit): HF + UN + Clen 2.13 ± 0.2 [52], HF + UN + Sal 1.42 ± 0.13 [38]; P < 0.05). Conclusion Clenbuterol treatment of failing rat hearts, alone or in combination with mechanical unloading, improves LV function at the whole-heart and cellular levels by affecting cell morphology, excitation–contraction coupling, and myofilament sensitivity to calcium. This study supports the use of this drug in the strategy to enhance recovery in HF patients treated with LVADs and also begins to elucidate some of the possible cellular mechanisms responsible for the improvement in LV function