Macrocytosis in Mitochondrial DNA Deletion Syndromes

Large single mtDNA (mitochondrial DNA) deletion syndrome is a rare inborn error of metabolism with variable heteroplasmy levels and clinical phenotype among affected individuals. Chronic progressive external ophthalmoplegia (CPEO) is the most common phenotype in adults with this form of mitochondrial disease [1-2]. The common CPEO clinical manifestations are ptosis and ophthalmoplegia. More variable phenotypic manifestations of CPEO (CPEO plus) include involvement of the peripheral nervous system and myopathy. Here, we describe a 62-year-old female with CPEO and the major mitochondrial DNA deletion present at 40% heteroplasmy, who had a coexistent previously undescribed CPEO phenotypic feature of persistent unexplained macrocytosis without anemia. Building on this case, we reviewed other major mtDNA deletion cases seen in our Adult Metabolic Diseases Clinic (AMDC) at the University of British Columbia, Vancouver, Canada from 2016 to 2022. The major mtDNA deletion cases (n=26) were compared with mtDNA missense variants identified in the clinic over the same period who acted as the comparison group (n=16). Of these, the most frequent diagnosis was maternally inherited diabetes and deafness (MIDD) and mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS). Ten out of 26 (38%) of mtDNA deletion patients had macrocytosis with elevated MCV (mean corpuscular volume), median (IQR, interquartile range) of 108fl (102-114fl). Seven of the patients with macrocytosis had no pertinent etiology. None of the comparison group had macrocytosis. There was a significant difference (P=0.000) between the MCV & MCH in the mtDNA deletion group compared to the comparison group. This communication sheds light on the association of macrocytosis with the mtDNA deletion syndrome. It would be of great interest to determine if the association is found in other mitochondrial disease clinic populations.

Re-evaluation of CBMN test reference values of persons continuously occupationally exposed to low doses of ionizing radiation in Serbia

When established, cytokinesis-block micronucleus (CBMN) test reference values should be periodically evaluated according to the recommendations of reference documents. The biodosimetry cytogenetic laboratory of the Serbian Institute of Occupational Health established the CBMN test reference range for people occupationally exposed to ionizing radiation in 2016. Since then, new occupationally exposed persons have been subjected to micronucleus testing, resulting in the need for re-evaluation of existing CBMN test values. The examined population comprised 608 occupationally exposed subjects - 201 from the previous laboratory database and 407 newly examined. Comparison of groups based on gender, age and cigarette consumption did not show significant differences, although certain CBMN values differed significantly between the old and new groups. Duration of occupational exposure, gender, age and smoking habit influenced micronuclei frequency in all three analyzed groups, while no relation was found between type of work and micronucleus test parameters. Since the mean values of all tested parameters in the new group of examinees are within previously established reference ranges, existing values can be used in further research.

Diagnostic yield from routine metabolic screening tests in evaluation of global developmental delay and intellectual disability

Global developmental delay and intellectual disability (GDD/ID) affect 3% of the paediatric population. Although inborn errors of metabolism (IEM) are not a common cause of GDD/ID, early therapeutic intervention can improve neurodevelopmental manifestations. In 2012, a first-tier test panel, including specialized metabolic and routine chemistry tests, was piloted to community-based paediatricians in British Columbia with aims to achieve earlier diagnosis of treatable IEM.

Objective

The aim of this retrospective review was to evaluate the diagnostic yield from these first-tier tests in the 7 years before (2006 to 2012) and after (2013 to 2019) implementation at the community paediatrician level.

Results

Prior and postimplementation diagnostic yield of an IEM from first-tier metabolic testing was 9 out of 986 (0.91%) and 11 out of 4,345 children (0.25%), respectively. Disorders of creatine metabolism and organic acidurias were the most frequently established diagnoses in both time periods. No diagnoses were established through acylcarnitine copper/ceruloplasmin, lactate, or ammonia testing. Twenty out of 24 patients had specific neurological or other red flag signs in addition to GDD/ID. Four boys diagnosed with an x-linked creatine transporter defect (CTD) had speech-language delay as the most prominent finding.

Conclusions

The expansion of first-tier metabolic testing to community-based paediatricians in BC did not yield an increase in IEM diagnoses. A modified first-tier test panel should be offered to patients with GDD/ID, neurologic, and/or red flag signs. Urine creatine testing in boys with speech-language delay warrants consideration to detect CTD.

Congenital lactic acidosis, cerebral cysts and pulmonary hypertension in an infant with FOXRED1 related complex 1 deficiency

Mitochondrial complex I is encoded by 38 nuclear-encoded and 7 mitochondrial-encoded genes. FOXRED1 is one of the 13 additional nuclear genes known as assembly factors. So far, four patients have been described with complex I deficiency caused by autosomal recessive mutations in FOXRED1.

Here, we report the fifth patient with FOXRED1 related complex 1 deficiency presenting with prenatal onset of bilateral periventricular cysts, congenital lactic acidosis, and persistent life-limiting pulmonary hypertension. Whole exome sequencing identified a compound heterozygosity for a known pathogenic variant (c.612_615dupAGTG; p.A206SfsX15) (paternal) and a likely pathogenic variant (c.874G>A; p.Gly292Arg) (maternal). Deficiency of complex I was demonstrated by the absence of complex I on Blue Native Gel Electrophoresis and by a significantly reduced complex I enzyme activity in the patient's fibroblasts.

Compared with the previous known FOXRED1 cases, unique clinical features observed in our patient include bilateral periventricular cysts and severe pulmonary hypertension. Whole exome sequencing was instrumental in recognizing the underlying gene defect in this patient.

Congenital lactic acidosis, cerebral cysts and pulmonary hypertension in an infant with FOXRED1 related complex I deficiency

Mitochondrial complex I is encoded by 38 nuclear-encoded and 7 mitochondrial-encoded genes. FOXRED1 is one of the 13 additional nuclear genes known as assembly factors. So far, four patients have been described with complex I deficiency caused by autosomal recessive mutations in FOXRED1.

Here, we report the fifth patient with FOXRED1 related complex 1 deficiency presenting with prenatal onset of bilateral periventricular cysts, congenital lactic acidosis, and persistent life-limiting pulmonary hypertension. Whole exome sequencing identified a compound heterozygosity for a known pathogenic variant (c.612_615dupAGTG; p.A206SfsX15) (paternal) and a likely pathogenic variant (c.874G > A; p.Gly292Arg) (maternal). Deficiency of complex I was demonstrated by the absence of complex I on Blue Native Gel Electrophoresis and by a significantly reduced complex I enzyme activity in the patient's fibroblasts.

Compared with the previous known FOXRED1 cases, unique clinical features observed in our patient include bilateral periventricular cysts and severe pulmonary hypertension. Whole exome sequencing was instrumental in recognizing the underlying gene defect in this patient.

Gene Expression Profiling of Endoplasmic Reticulum Stress in Hepatitis C Virus-Containing Cells Treated with an Inhibitor of Protein Disulfide Isomerases

Protein disulfide isomerases (PDIs) catalyze disulfide bond formation between protein cysteine residues during protein folding in the endoplasmic reticulum (ER) lumen and are essential for maintaining ER homoeostasis. The life cycle of the hepatitis C virus (HCV) is closely associated with the ER. Synthesis and maturation of HCV proteins occur in the ER membrane and are mediated by multiple host cell factors that include also PDI. Here, we present a study investigating the effect of PDI inhibition on Huh7 human hepatoma cells harboring an HCV subgenomic replicon using the abscisic acid-derived PDI inhibitor origamicin. Transcriptional profiling shows that origamicin changed the expression levels of genes involved in the oxidative and ER stress responses and the unfolded protein response, as indicated by the upregulation of antioxidant enzymes and chaperone proteins, the downregulation of cell-cycle proteins, and induction of apoptosis-associated genes. Our data suggest that origamicin negatively impacts HCV replication by causing an imbalance in cellular homoeostasis and induction of stress responses. These insights suggest that inhibition of PDIs by low-molecular-weight inhibitors could be a promising approach to the discovery of novel antiviral compounds.

Sialic acid catabolism by N-acetylneuraminate pyruvate lyase is essential for muscle function

Sialic acids are important components of glycoproteins and glycolipids essential for cellular communication, infection, and metastasis. The importance of sialic acid biosynthesis in human physiology is well illustrated by the severe metabolic disorders in this pathway. However, the biological role of sialic acid catabolism in humans remains unclear. Here, we present evidence that sialic acid catabolism is important for heart and skeletal muscle function and development in humans and zebrafish. In two siblings, presenting with sialuria, exercise intolerance/muscle wasting, and cardiac symptoms in the brother, compound heterozygous mutations [chr1:182775324C>T (c.187C>T; p.Arg63Cys) and chr1:182772897A>G (c.133A>G; p.Asn45Asp)] were found in the N-acetylneuraminate pyruvate lyase gene (NPL). In vitro, NPL activity and sialic acid catabolism were affected, with a cell-type-specific reduction of N-acetyl mannosamine (ManNAc). A knockdown of NPL in zebrafish resulted in severe skeletal myopathy and cardiac edema, mimicking the human phenotype. The phenotype was rescued by expression of wild-type human NPL but not by the p.Arg63Cys or p.Asn45Asp mutants. Importantly, the myopathy phenotype in zebrafish embryos was rescued by treatment with the catabolic products of NPL: N-acetyl glucosamine (GlcNAc) and ManNAc; the latter also rescuing the cardiac phenotype. In conclusion, we provide the first report to our knowledge of a human defect in sialic acid catabolism, which implicates an important role of the sialic acid catabolic pathway in mammalian muscle physiology, and suggests opportunities for monosaccharide replacement therapy in human patients.

Exome Sequencing and the Management of Neurometabolic Disorders

BACKGROUND

Whole-exome sequencing has transformed gene discovery and diagnosis in rare diseases. Translation into disease-modifying treatments is challenging, particularly for intellectual developmental disorder. However, the exception is inborn errors of metabolism, since many of these disorders are responsive to therapy that targets pathophysiological features at the molecular or cellular level.

METHODS

To uncover the genetic basis of potentially treatable inborn errors of metabolism, we combined deep clinical phenotyping (the comprehensive characterization of the discrete components of a patient's clinical and biochemical phenotype) with whole-exome sequencing analysis through a semiautomated bioinformatics pipeline in consecutively enrolled patients with intellectual developmental disorder and unexplained metabolic phenotypes.

RESULTS

We performed whole-exome sequencing on samples obtained from 47 probands. Of these patients, 6 were excluded, including 1 who withdrew from the study. The remaining 41 probands had been born to predominantly nonconsanguineous parents of European descent. In 37 probands, we identified variants in 2 genes newly implicated in disease, 9 candidate genes, 22 known genes with newly identified phenotypes, and 9 genes with expected phenotypes; in most of the genes, the variants were classified as either pathogenic or probably pathogenic. Complex phenotypes of patients in five families were explained by coexisting monogenic conditions. We obtained a diagnosis in 28 of 41 probands (68%) who were evaluated. A test of a targeted intervention was performed in 18 patients (44%).

CONCLUSIONS

Deep phenotyping and whole-exome sequencing in 41 probands with intellectual developmental disorder and unexplained metabolic abnormalities led to a diagnosis in 68%, the identification of 11 candidate genes newly implicated in neurometabolic disease, and a change in treatment beyond genetic counseling in 44%. (Funded by BC Children's Hospital Foundation and others.).

Structure-based mutagenic analysis of mechanism and substrate specificity in mammalian glycosyltransferases: porcine ST3Gal-I

Sialyltransferases (STs) play essential roles in signaling and in the cellular recognition processes of mammalian cells by selectively installing cell-surface sialic acids in an appropriate manner both temporally and organ-specifically. The availability of the first three-dimensional structure of a mammalian (GT29) sialyltransferase has, for the first time, allowed quantitative structure/function analyses to be performed, thereby providing reliable insights into the roles of key active site amino acids. Kinetic analyses of mutants of ST3Gal-I, in conjunction with structural studies, have confirmed the mechanistic roles of His302 and His319 as general acid and base catalysts, respectively, and have quantitated other interactions with the cytosine monophosphate-N-acetyl β-neuraminic acid donor substrate. The contributions of side chains that provide key interactions with the acceptor substrate, defining its specificity, have also been quantitated. Particularly important transition-state interactions of 2.5 and 2.7 kcal mol(-1) are found between the acceptor axial 4-hydroxyl and the conserved side chains of Gln108 and Tyr269, respectively. These results provide a basis for the engineering of mammalian STs to accommodate non-natural substrate analogs that should prove valuable as chemical biological probes of sialyltransferase function.

Review of retrospective dosimetry techniques for external ionising radiation exposures

The current focus on networking and mutual assistance in the management of radiation accidents or incidents has demonstrated the importance of a joined-up approach in physical and biological dosimetry. To this end, the European Radiation Dosimetry Working Group 10 on 'Retrospective Dosimetry' has been set up by individuals from a wide range of disciplines across Europe. Here, established and emerging dosimetry methods are reviewed, which can be used immediately and retrospectively following external ionising radiation exposure. Endpoints and assays include dicentrics, translocations, premature chromosome condensation, micronuclei, somatic mutations, gene expression, electron paramagnetic resonance, thermoluminescence, optically stimulated luminescence, neutron activation, haematology, protein biomarkers and analytical dose reconstruction. Individual characteristics of these techniques, their limitations and potential for further development are reviewed, and their usefulness in specific exposure scenarios is discussed. Whilst no single technique fulfils the criteria of an ideal dosemeter, an integrated approach using multiple techniques tailored to the exposure scenario can cover most requirements.

Structure and mechanism of the lipooligosaccharide sialyltransferase from Neisseria meningitidis

The first x-ray crystallographic structure of a CAZY family-52 glycosyltransferase, that of the membrane associated α2,3/α2,6 lipooligosaccharide sialyltransferase from Neisseria meningitidis serotype L1 (NST), has been solved to 1.95 Å resolution. The structure of NST adopts a GT-B-fold common with other glycosyltransferase (GT) families but exhibits a novel domain swap of the N-terminal 130 residues to create a functional homodimeric form not observed in any other class to date. The domain swap is mediated at the structural level by a loop-helix-loop extension between residues Leu-108 and Met-130 (we term the swapping module) and a unique lipid-binding domain. NST catalyzes the creation of α2,3- or 2,6-linked oligosaccharide products from a CMP-sialic acid (Neu5Ac) donor and galactosyl-containing acceptor sugars. Our structures of NST bound to the non-hydrolyzable substrate analog CMP-3F((axial))-Neu5Ac show that the swapping module from one monomer of NST mediates the binding of the donor sugar in a composite active site formed at the dimeric interface. Kinetic analysis of designed point mutations observed in the CMP-3F((axial))-Neu5Ac binding site suggests potential roles of a requisite general base (Asp-258) and general acid (His-280) in the NST catalytic mechanism. A long hydrophobic tunnel adjacent to the dimer interface in each of the two monomers contains electron density for two extended linear molecules that likely belong to either the two fatty acyl chains of a diglyceride lipid or the two polyethylene glycol groups of the detergent Triton X-100. In this work, Triton X-100 maintains the activity and increases the solubility of NST during purification and is critical to the formation of ordered crystals. Together, the mechanistic implications of the NST structure provide insight into lipooligosaccharide sialylation with respect to the association of substrates and the essential membrane-anchored nature of NST on the bacterial surface.

Arabidopsis histone deacetylase 6: a green link to RNA silencing

Epigenetic reprogramming is at the base of cancer initiation and progression. Generally, genome-wide reduction in cytosine methylation contrasts with the hypermethylation of control regions of functionally well-established tumor suppressor genes and many other genes whose role in cancer biology is not yet clear. While insight into mechanisms that induce aberrant cytosine methylation in cancer cells is just beginning to emerge, the initiating signals for analogous promoter methylation in plants are well documented. In Arabidopsis, the silencing of promoters requires components of the RNA interference machinery and promoter double-stranded RNA (dsRNA) to induce a repressive chromatin state that is characterized by cytosine methylation and histone deacetylation catalysed by the RPD3-type histone deacetylase AtHDA6. Similar mechanisms have been shown to occur in fission yeast and mammals. This review focuses on the connections between cytosine methylation, dsRNA and AtHDA6-controlled histone deacetylation during promoter silencing in Arabidopsis and discusses potential mechanistic similarities of these silencing events in cancer and plant cells.

A small-molecule probe for hepatitis C virus replication that blocks protein folding

The hepatitis C virus (HCV) is a growing global health problem. Small molecules that interfere with host-viral interactions can serve as powerful tools for elucidating the molecular mechanisms of pathogenesis and defining new strategies for therapeutic development. Using a cell-based screen involving subgenomic HCV replicons, we identified the ability of 18 different abscisic acid (ABA) analogs, originally developed as plant growth regulators, to inhibit HCV replication. Three of these were further studied. One compound, here named origamicin, showed antiviral activity through the inhibition of host proteins involved in protein folding. Origamicin could therefore be an important tool for studying the maturation of both host and viral proteins. Herein we demonstrate an application for molecular scaffolds based on ABA for mammalian cell targets involved in protein folding.

Peroxisome proliferator-activated receptor alpha antagonism inhibits hepatitis C virus replication

Hepatitis C virus (HCV) is a global health problem and a leading cause of liver disease. Here, we demonstrate that the replication of HCV replicon RNA in Huh-7 cells is inhibited by a peroxisome proliferator-activated receptor (PPAR) antagonist, 2-chloro-5-nitro-N-(pyridyl)benzamide (BA). Downregulation of PPARgamma with RNA interference approaches had no effect on HCV replication in Huh-7 cells, whereas PPARalpha downregulation inhibited HCV replication. Fluorescence and coherent anti-Stokes Raman scattering (CARS) microscopy demonstrate a clear buildup of lipids upon treatment with BA. These observations are consistent with the misregulation of lipid metabolism, phospholipid secretion, cholesterol catabolism, and triglyceride clearance events associated with the inhibition of PPARalpha. The inhibition of HCV replication by BA may result from disrupting lipidation of host proteins associated with the HCV replication complex or, more generally, by disrupting the membranous web where HCV replicates.

Exploring New Chemical Space by Stereocontrolled Diversity-Oriented Synthesis

Natural products that act as highly specific, small-molecule protein-binding agents and as modulators of protein-protein interactions are highly complex and exhibit functional groups with three-dimensional and stereochemical diversity. The complex three-dimensional display of chiral functional groups appears to be crucial for exhibiting specificity in protein binding and in differentiating between closely related proteins. The development of methods that allow a high-throughput access to three-dimensional, skelatally complex, polycyclic compounds having few asymmetric diversity sites is essential and a highly challenging task. In the postgenomic chemical biology age, in which there is a great desire to understand protein-protein interactions and to dissect protein networking-based signaling pathways by small molecules, the need for developing "stereocontrolled, diversity-oriented synthesis" methods to generate natural product-like libraries is of utmost importance.

[Significance of serum creatinine levels in respiratory insufficiency conditions]

Analyses of creatinema in the cases of global respiratory failure was performed in this paper. The patients with global respiratory failure treated in General Hospital in TeSanj have been followed. For all patients laboratory analyses have been performed on the admimtion and in the time of clinical status improvement, including creatinin level, K, Na, Hb, Htc, and blood gas analyses with mesurement of pO2 pCO2 pH, BE, saturation of the blood with oxgen, BE and HCO3-. Creatinine level have been considered in coleration of body mass index, and general nutritional status. The dinamic source of creatinine level in the blood have been followed, in relation of parameters of respiratory status. The statistical significance in relation of creatinine level with the respiratory status was registrated. With the improvement of respiratory status and laboratory analyses related to respiratory status, decrease of creatinin level was registrated. Because of that the therapy given to the patients with respiratory failure could influence on potassium level, the relation of creatinnemia and potassium level in the blood wasn't considered. The high creatinin level couldn't be explained with the initial renal failure, but as the sign of metbolic adaptation to hypoxemic and hypoxyc situation on the body. The registration of high creatinine level in the situations of global respiratory failure could be the guidelines for the choice of the antibiotics for these patients, mostly for potentially nephrotoxic antibiotics, like aminoglicosides, and theirs combinations. The decision and evaluation of benefit and toxicity of antibiotics for these situations could be easier.