Three Main Causes of Homocystinuria: CBS, cblC and MTHFR Deficiency. What do they Have in Common?

Propionic Acidemia, Methylmalonic Acidemia, and Cobalamin C Deficiency: Comparison of Untargeted Metabolomic Profiles

Methylmalonic acidemia (MMA), propionic acidemia (PA), and cobalamin C deficiency (cblC) share a defect in propionic acid metabolism. In addition, cblC is also involved in the process of homocysteine remethylation. These three diseases produce various phenotypes and complex downstream metabolic effects. In this study, we used an untargeted metabolomics approach to investigate the biochemical differences and the possible connections among the pathophysiology of each disease. The significantly changed metabolites in the untargeted urine metabolomic profiles of 21 patients (seven MMA, seven PA, seven cblC) were identified through statistical analysis (p < 0.05; log2FC > |1|) and then used for annotation. Annotated features were associated with different metabolic pathways potentially involved in the disease's development. Comparative statistics showed markedly different metabolomic profiles between MMA, PA, and cblC, highlighting the characteristic species for each disease. The most affected pathways were related to the metabolism of organic acids (all diseases), amino acids (all diseases), and glycine and its conjugates (in PA); the transsulfuration pathway; oxidative processes; and neurosteroid hormones (in cblC). The untargeted metabolomics study highlighted the presence of significant differences between the three diseases, pointing to the most relevant contrast in the cblC profile compared to MMA and PA. Some new biomarkers were proposed for PA, while novel data regarding the alterations of steroid hormone profiles and biomarkers of oxidative stress were obtained for cblC disease. The elevation of neurosteroids in cblC may indicate a potential connection with the development of ocular and neuronal deterioration.

METHYLATION-ASSOCIATED PATHWAYS IN MACULAR TELANGIECTASIA TYPE 2 AND OPHTHALMOLOGIC FINDINGS IN PATIENTS WITH GENETIC METHYLATION DISORDERS

PURPOSE

Serine (Ser) and glycine (Gly) levels were reported to differ between patients with macular telangiectasia type 2 (MacTel) compared with healthy controls. Because they are closely related to methylation metabolism, this report investigates methylation-associated metabolite levels in patients with MacTel and retinal changes in monogenetic methylation disorders.

METHODS

Prospective, monocentric study on patients with MacTel and healthy controls underwent a standardized protocol including a blood draw. Methylation-associated metabolite levels in plasma were determined using targeted quantitative metabolomics. Furthermore, patient records of cystathionine beta-synthase, methylenetetrahydrofolate reductase, and methylmalonic aciduria and homocystinuria type C protein (MMACHC) deficiency were screened for reported retinal changes.

RESULTS

In total, 29 patients with MacTel and 27 healthy controls were included. Patients with MacTel showed lower plasma Ser ( P = 0.02 and P = 0.01) and Gly ( P = 0.11 and P = 0.11) levels than controls. Principal component analyses revealed that methylation-associated metabolite, especially homocysteine, contributed to a distinct clustering of patients with MacTel. No retinal changes were seen in cystathionine beta-synthase (n = 1) and methylenetetrahydrofolate reductase (n = 2) deficiency, while two patients with MMACHC (n = 4) deficiency displayed extensive macular dystrophy.

CONCLUSION

Patients with MacTel show distinct clustering of methylation-associated metabolite compared with controls. Of the three homocystinurias, only MMACHC resulted in macular dystrophy, possibly due to distinct compensatory pathways.

A case of functional vitamin B12 deficiency after recreational nitrous oxide use

The recreational use of nitrous oxide as laughing gas becomes a real public health issue among adolescents and young adults. Chronic use is deleterious and can lead to severe neurological disorders. Nitrous oxide inactivates vitamin B12, and the functional defect of vitamin B12 plays a major role in the pathogenesis of nitrous oxide-related neurological disorders. Here we report the case of a 22-year-old woman who came to the hospital after an unexplained loss of consciousness. She exhibited typical features of vitamin B12 or folate deficiency such as macrocytic anemia and hypersegmented neutrophils. However, serum concentrations of folate and vitamin B12 were normal. In contrast, circulating concentrations of total homocysteine and methylmalonic acid were significantly increased. These results clearly indicated a defect in vitamin B12 functions. The reason for this defect was clarified when she revealed that she had been consuming nitrous oxide recreationally for over a year. The present case points out the challenges in diagnosing vitamin B12 deficiency in the context of nitrous oxide abuse due to normal concentrations of total serum vitamin B12 in a significant proportion of cases. The medical community should be aware of how difficult it can be to interpret B12 status in this specific population.

Hyperhomocysteinemia in acute hepatic porphyria (AHP) and implications for treatment with givosiran

INTRODUCTION

Homocysteine is a sulfur-containing amino acid formed in the intermediary metabolism of methionine. Amino acid metabolism and heme biosynthesis pathways are complexly intertwined. Plasma homocysteine elevation, hyperhomocysteinemia (HHcy), has been reported in patients with acute hepatic porphyria (AHP), a family of rare genetic disorders caused by defects in hepatic heme biosynthesis.

AREAS COVERED

This article summarizes published case series in which givosiran, a subcutaneously administered small interfering RNA approved for AHP treatment, appeared to exacerbate dysregulated homocysteine metabolism in patients with AHP. A comprehensive exploratory analysis of ENVISION trial data demonstrated that on a population level, givosiran increased homocysteine but with wide interpatient variations, and there is no proof of correlations between HHcy and changes in efficacy or safety of givosiran.

EXPERT OPINION

The strong correlation and co-increase of homocysteine and methionine suggest that HHcy associated with givosiran is likely attributable to the impaired trans-sulfuration pathway catalyzed by cystathionine β-synthase, which uses vitamin B6 as a cofactor. Data-based consensus supports monitoring total plasma homocysteine and vitamin B6, B12, and folate levels before and during givosiran treatment; supplementing with pyridoxine/vitamin B6 in patients with homocysteine levels >100 μmol/L; and involving patients with homocysteine levels >30 μmol/L in decisions to supplement.

Genes Responsible for H2S Production and Metabolism Are Involved in Learning and Memory in Drosophila melanogaster

The gasotransmitter hydrogen sulfide (H₂S) produced by the transsulfuration pathway (TSP) is an important biological mediator, involved in many physiological and pathological processes in multiple higher organisms, including humans. Cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) enzymes play a central role in H₂S production and metabolism. Here, we investigated the role of H₂S in learning and memory processes by exploring several Drosophila melanogaster strains with single and double deletions of CBS and CSE developed by the CRISPR/Cas9 technique. We monitored the learning and memory parameters of these strains using the mating rejection courtship paradigm and demonstrated that the deletion of the CBS gene, which is expressed predominantly in the central nervous system, and double deletions completely block short- and long-term memory formation in fruit flies. On the other hand, the flies with CSE deletion preserve short- and long-term memory but fail to exhibit long-term memory retention. Transcriptome profiling of the heads of the males from the strains with deletions in Gene Ontology terms revealed a strong down-regulation of many genes involved in learning and memory, reproductive behavior, cognition, and the oxidation–reduction process in all strains with CBS deletion, indicating an important role of the hydrogen sulfide production in these vital processes.

RESEARCH OF INDICATORS OF OXIDATIVE STRESS IN THE KIDNEYS OF IMMATURE RATS WITH HYPERHOMOCYSTEINEMIA

Purpose: Hyperhomocysteinemia in children can develop as a result of genetic defects, endocrine abnormalities or under the influence of dietary factors. An elevated level of homocysteine is considered a risk factor for the progression of chronic kidney disease. The aim of the work was to investigate the indicators of oxidative stress in the homogenate of the kidneys of immature rats in control and with hyperhomocysteinemia. Methods: The concentration of reduced and oxidized glutathione, the activity of superoxide dismutase, catalase and nitric oxide synthase were determined. The model of hyperhomocysteinemia was reproduced on one-month-old male rats, which were kept on a standard vivarium diet. The experimental group was intragastrically administered by D,L-thiolactone homocysteine hydrochloride in a 1% starch solution at a dose of 200 mg/kg of body weight 1 per day for 8 weeks. The corresponding volume of 1% starch solution was injected into the control group of animals. The activity of superoxide dismutase, catalase and nitric oxide synthase were determined spectrophotometrically. Concentration of reduced and oxidized glutathione by fluorometric method. Results: It was established that upon hyperhomocysteinemia the concentration of reduced glutathione, the activity of superoxide dismutase, catalase, and nitric oxide synthase was decreased against the background of an increase in the concentration of oxidized glutathione in the homogenate of the kidneys of immature rats. Conclusions: The obtained results indicate that in the kidneys of immature rats, the development of oxidative stress occurs in the direction characteristic of adult animals. The obtained results indicate that in the kidneys of immature rats the development of oxidative stress resembles the adult animals. The obtained results showed a decrease in the concentration of reduced glutathione and the activity of antioxidant defense enzymes which may indicate the development of pathological processes in the kidneys

Long-term outcome of a patient with Transcobalamin deficiency caused by the homozygous c.1115_1116delCA mutation in TCN2 gene: a case report

BACKGROUND

Transcobalamin deficiency is a rare autosomal recessive inborn error of cobalamin transport (prevalence: < 1/1000000) which clinically manifests in early infancy.

CASE PRESENTATION

We describe the case of a 31 years old woman who at the age of 30 days presented with the classical clinical and laboratory signs of an inborn error of vitamin B₁₂ metabolism. Family history revealed a sister who died at the age of 3 months with a similar clinical syndrome and with pancytopenia. She was started on empirical intramuscular (IM) cobalamin supplements (injections of hydroxocobalamin 1 mg/day for 1 week and then 1 mg twice a week) and several transfusions of washed and concentrated red blood cells. With these treatments a clear improvement in symptoms was observed, with the disappearance of vomiting, diarrhea and normalization of the full blood count. At 8 years of age injections were stopped for about two and a half months causing the appearance of pancytopenia. IM hydroxocobalamin was then restarted sine die. The definitive diagnosis could only be established at 29 years of age when a genetic evaluation revealed the homozygous c.1115_1116delCA mutation of TCN2 gene (p.Q373GfsX38). Currently she is healthy and she is taking 1 mg of IM hydroxocobalamin once a week.

CONCLUSIONS

Our case report highlights that early detection of TC deficiency and early initiation of aggressive IM treatment is likely associated with disease control and an overall favorable outcome.

Methylenetetrahydrofolate reductase polymorphisms as genetic markers to predict homocysteinemia and clinical severity in sickle cell disease

Aim: The present study observed the relationship between the methylenetetrahydrofolate reductase genotypes and clinical outcome in children with sickle cell disorder. Methodology: A total of 249 children were recruited for the study and evaluated clinically for calculating severity score, homocysteine levels and C677T and A1298C genotyping. Results: The frequencies of variant genotypes were 28.1% CT/TT677 and 69.1% AC/CC1298. Plasma homocysteine was significantly elevated in variant groups (p < 0.001). Both the genotypes accorded significant association with homocysteinemia (p < 0.001). Vascular crisis (p = 0.04), frequency of hospitalization (p < 0.001) and severity score (p = 0.02) revealed association with C677T and not with A1298C. The CT/TT677 genotypes showed 3.39-times (p = 0.032) increase in a higher score for severity. Conclusion: C677T depicted significant association with clinical severity in study population.

Molecular and biochemical investigations of inborn errors of metabolism-altered redox homeostasis in branched-chain amino acid disorders, organic acidurias, and homocystinuria

India, resembling other developing nations, is confronting a hastening demographic switch to non-communicable diseases. Inborn errors of metabolism (IEM) constitute a varied heterogeneous group of disorders with variable clinical appearance, primarily in the pediatric populace. Congenital deformities and genetic disorders are significant for mortality throughout the world, and the Indian scenario is not very different. IEMs are a group of monogenic issues described by dysregulation of the metabolic networks that bring about development and homeostasis. Incipient evidence focuses on oxidative stress and mitochondrial dysfunction as significant contributors to the multiorgan modifications are detected in a few IEMs. The amassing of toxic metabolites in organic acidurias, respiratory chain, and fatty acid oxidation ailments inhibit mitochondrial enzymes and processes, bringing about elevated levels of reactive oxygen species (ROS). In different IEMs, as in homocystinuria, various sources of ROS have been suggested. In patients' samples along with cellular and experimental animal models, a few investigations have recognized substantial increments in ROS levels alongside diminishes in antioxidant defenses, relating with oxidative damage to proteins, lipids as well as DNA. Elevated ROS levels interrupt redox signaling pathways controlling biological processes such as cell development, differentiation, or apoptosis; however, few investigations explore these processes in IEMs. This review depicts the mitochondrial dysfunction, oxidative stress, redox signaling in branched-chain amino acid disorders, further organic acidurias, and homocystinuria, alongside the latest research investigating the proficiency of antioxidants in addition to mitochondria-targeted therapies as therapeutic components in these diseases.