Plasma homocysteine in patients with retinal vein occlusion

CENTRAL RETINAL VEIN OCCLUSION IN 12-YEAR-OLD GIRL WITH METHYLENETETRAHYDROFOLATE REDUCTASE MUTATION: A CASE REPORT AND REVIEW OF THE LITERATURE

PURPOSE

This case report describes a central retinal vein occlusion in a healthy 12-year-old girl who developed retinal neovascularization at 24 years of age. To the knowledge of the authors, this is the longest time between a reported pediatric central retinal vein occlusion event and neovascularization.

METHODS

The patient underwent a full history, physical examination, and laboratory workup to determine potential risk factors contributing to the vascular event. Fundus photographs, optical coherence tomography, and fluorescein angiography were performed throughout the patient's treatment course.

RESULTS

Family history was noncontributory, but laboratory testing revealed a mildly elevated homocysteine level and homozygous C677T mutation in methylenetetrahydrofolate reductase. As a result, she was started on folate supplementation. The patient has had no further ocular or systemic thrombotic events to date.

CONCLUSION

Pediatric patients presenting with central retinal vein occlusion should undergo a systemic workup and require long-term follow-up to avoid complications, such as intraocular hemorrhage, tractional retinal detachments, and neovascular glaucoma.

Prevention and Treatment of Retinal Vein Occlusion: The Role of Diet-A Review

Retinal vein occlusion (RVO) is the second most common retinal disorder. In comparison to diabetic retinopathy or age-related macular degeneration, RVO is usually an unexpected event that carries a greater psychological impact. There is strong evidence to suggest that cardiovascular diseases are the most common risk factors in this pathology and it has long been known that a higher consumption of fish, nuts, fruits, and vegetables has a protective effect against these types of conditions. In the last several years, interest in plant-based diets has grown in both the general population and in the scientific community, to the point to which it has become one of the main dietary patterns adopted in Western countries. The aim of this review is to investigate the potential impact of macro- and micronutrients on retinal vein occlusion.

Emerging applications of bioinformatics and artificial intelligence in the analysis of biofluid markers involved in retinal occlusive diseases: a systematic review

PURPOSE

To review the literature on the application of bioinformatics and artificial intelligence (AI) for analysis of biofluid biomarkers in retinal vein occlusion (RVO) and their potential utility in clinical decision-making.

METHODS

We systematically searched MEDLINE, Embase, Cochrane, and Web of Science databases for articles reporting on AI or bioinformatics in RVO involving biofluids from inception to August 2021. Simple AI was categorized as logistics regressions of any type. Risk of bias was assessed using the Joanna Briggs Institute Critical Appraisal Tools.

RESULTS

Among 10,264 studies screened, 14 eligible articles, encompassing 578 RVO patients, met the inclusion criteria. The use and reporting of AI and bioinformatics was heterogenous. Four articles performed proteomic analyses, two of which integrated AI tools such as discriminant analysis, probabilistic clustering, and string pathway analysis. A metabolomic study used AI tools for clustering, classification, and predictive modeling such as orthogonal partial least squares discriminant analysis. However, most studies used simple AI (n = 9). Vitreous humor sample levels of interleukin-6 (IL-6), vascular endothelial growth factor (VEGF), and aqueous humor levels of intercellular adhesion molecule-1 and IL-8 were implicated in the pathogenesis of branch RVO with macular edema. IL-6 and VEGF may predict visual acuity after intravitreal injections or vitrectomy, respectively. Metabolomics and Kyoto Encyclopedia of Genes and Genomes enrichment analysis identified the metabolic signature of central RVO to be related to lower aqueous humor concentration of carbohydrates and amino acids. Risk of bias was low or moderate for included studies.

CONCLUSION

Bioinformatics has applications for analysis of proteomics and metabolomics present in biofluids in RVO with AI for clinical decision-making and advancing the future of RVO precision medicine. However, multiple limitations such as simple AI use, small sample volume, inconsistent feasibility of office-based sampling, lack of longitudinal follow-up, lack of sampling before and after RVO, and lack of healthy controls must be addressed in future studies.

Vitamin B12 levels in patients with retinal vein occlusion and their relation with clinical outcome: a retrospective study

Retinal vein occlusion (RVO) is the second most common retinal vascular disorder, after diabetic retinopathy. Most patients suffering RVO develop some degree of visual loss consequent to retinal complications such as edema and microhemorrhages. Even if some risk factors for RVO have been identified, the clinical outcome of RVO remains highly unpredictable because studies investigating potential prognostic markers for visual improvement are lacking. Cyanocobalamin belongs to the group of B vitamins and plays a role in homocysteine metabolism; however, cyanocobalamin deficiency associates with an increase of some toxic bioproducts involved in endothelial injury and platelet activation independent of homocysteine levels. We retrospectively evaluated the levels of vitamin B12 at diagnosis in 203 patients with RVO, and in a parallel cohort of 120 age- and sex-matched patients without RVO from an internal medicine ward, and correlated them with visual outcome at follow-up (median time 150 days, IQR 30-210). In patients with RVO, vitamin B12 levels at diagnosis were significantly lower than in controls and independently predicted worse clinical outcome at multivariate analysis (OR 3.2; CIs 1.2-8.2; p = 0.015). Our data suggest the opportunity to prospectively evaluate the effect on visual outcome of cyanocobalamin supplementation in RVO patients.

Paracentral acute middle maculopathy (PAMM) associated with ulcerative colitis and coexisting hyperhomocysteinemia: A case report

Introduction:

Paracentral acute middle maculopathy (PAMM) is a tomographic finding of a retinal occlusive vascular disorders with different aetiologies. Despite the well documented triple association among hyper-homocysteine, retinal vein occlusion and PAMM, up to date no reports exist on the development of PAMM in young patients affected by ulcerative colitis (UC).

Case description:

A multimodal imaging study, including fundus photographs, optical coherence tomography (OCT) B-scans, OCT angiography (OCT-A) and fluorescein and indocyanine green angiography, was performed in a 32-years-old male complaining of acute-onset paracentral scotoma in the right eye. Fundus images demonstrated the typical dark gray area of retinal capillary ischemia, corresponding on OCT B-scans to the hyper-reflective plaques in the INL, and consistent with PAMM lesions.The deep capillary plexus (DCP) was normal on OCT-A. Fluorescein angiography revealed a concurrent branch retinal vein preocclusion and showed capillary drop out parafoveally. Patient’s anamnesis was negative except for a 15-years history of UC and use of acetylsalicylic acid (ASS). At the time of presentation, UC was quiescent, but new blood tests revealed concomitant high values of homocysteinemia requiring oral vitamin B12 and folate supplementation. Two months later PAMM lesions had disappeared on OCT B-scans and a retinal thinning at the level of the inner nuclear layer (INL) was visible. The DCP on OCT-A remained unchanged without any sign of capillary ischemia.

Conclusions:

Although no definitive evidence directly links UC with PAMM, the latter should be suspected in young patients affected by IBD with coexisting hyper-homocysteinemia and unexplained visual symptoms.

Lipid profile and serum folate, vitamin B12 and homocysteine levels in patients with retinal vein occlusion

BACKGROUND

Retinal vein occlusion (RVO) is mainly related with vascular risk factors (VRF).

OBJECTIVES

To analyze the lipid profile and serum folate, vitamin B₁₂ and homocysteine levels, in patients with RVO and a population-based control group.

PATIENTS AND METHODS

Case-control study. Patients with RVO were assessed during an 11-year period.

RESULTS

We included 368 patients and 325 controls of similar age and sex. HDL cholesterol and folate levels were lower (52 [43-63] mg/dL vs. 55 [46-66]; p = 0.016 and 7 [5-10] ng/mL vs. 9 [7-13]; p < 0.0001, respectively) and non-HDL cholesterol and homocysteine levels higher (148.9 ± 37.3 mg/dL vs. 142.9 ± 34.5; p = 0.03 and 13.4 [11.2-18.2] μmol/L vs. 11.1 [9.0-14.4]; p < 0.001) in patients with RVO than controls. Although total cholesterol, LDL-C, and triglyceride levels were higher and serum vitamin B₁₂ levels were lower in RVO patients, these differences did not reach statistical significance.

CONCLUSIONS

RVO-patients have lower serum HDL-C and folate levels and higher non-HDL-C and serum homocysteine levels than population-based controls of similar age and sex. In patients with RVO, apart from the lipid profile, determination of serum homocysteine, folate and vitamin B₁₂ levels might be useful, as well as the treatment of their alterations.

Vitamin B12 and Folate as Risk Factors for Retinal Vein Occlusion: A Meta-Analysis

PURPOSE

To evaluate the association between serum vitamin B12/folate and retinal vein occlusion (RVO).

METHODS

A comprehensive search of the PubMed database was performed, which identified 271 abstracts to be screened. Ten studies met our inclusion criteria and a meta-analysis of these comparative case-control studies was performed on the mean ± standard deviation serum vitamin B12 and folate levels, without language restrictions. Nine studies with 720 patients with RVO and 613 controls were included in the meta-analysis for vitamin B12, and 10 studies with 784 patients with RVO and 677 controls in the meta-analysis for folate.

RESULTS

There was no statistically significant difference between patients with RVO and controls in serum vitamin B12 levels (mean difference: - 40.25 pg/mL, p = 0.28), either central RVO (mean difference: - 18.24 pg/mL, p = 0.71) or branch RVO (mean difference: - 23.56 pg/mL, p = 0.48). On the contrary, the plasma folate level was significantly lower in RVO patients than in controls (mean difference: - 1.34 ng/mL, p = 0.001), as well as in patients with CRVO compared to controls (mean difference: - 1.48 ng/mL, p = 0.006), but not in BRVO patients (mean difference: - 0.72 ng/mL, p = 0.11).

CONCLUSIONS

RVO is associated with low serum folate levels, but not with serum vitamin B12 levels.

Perineuritis or infiltration of optic nerve sheath? A presentation of diffuse large B cell Gastric lymphoma

Optic perineuritis is an inflammatory disorder involving the optic nerve sheath. It is currently considered as a part of idiopathic orbital inflammatory disease which also includes dacryoadenitis, orbital myositis, superior orbital fissure, and cavernous sinus syndrome (Tolosa hunt syndrome). As it is idiopathic, it is considered a diagnosis of exclusion. Another important differential is optic nerve lymphoma. Isolated optic nerve lymphoma associated with systemic involvement has been described in literature. We report a case that presented as third nerve palsy but later on developed central retinal vein occlusion and was ultimately diagnosed as primary gastric lymphoma of diffuse large B cell type.

Methylenetetrahydrofolate reductase polymorphisms as risk factors for retinal venous occlusive disease: A literature review

The role of polymorphisms of methylenetetrahydrofolate reductase (MTHFR) gene in retinal vein occlusion (RVO) is a theme of discussion since the first reports of RVO in patients with MTHFR C677T mutation and without classic acquired risk factors for retinal vascular disease. The association between MTHFR polymorphisms and RVO has been studied over the last 20 years producing conflicting results. This review aims to summarize the literature concerning the role MTHFR polymorphisms as risk factors for RVO.

N-Methyl-D-aspartate receptor activation, novel mechanism of homocysteine-induced blood-retinal barrier dysfunction

Elevated levels of amino acid homocysteine (Hcy) recognized as hyperhomocysteinemia (HHcy) was reported in several human visual disorders, such as diabetic retinopathy (DR) and age-related macular degeneration (AMD). Breakdown of blood-retinal barrier (BRB) is concomitant with vision loss in DR and AMD. We previously reported that HHcy alters BRB. Here, we tested the hypothesis that HHcy alters BRB via activation of N-methyl-D-aspartate receptor (NMDAR). Human retinal endothelial cells subjected to high level of Hcy and mouse model of HHcy were used. We injected Hcy intravitreal and used a mouse model of HHcy that lacks cystathionine-β-synthase (CBS). RT-PCR, western blot, and immunofluorescence showed that retinal endothelial cells (RECs) express NMDAR at the gene and protein levels both in vitro and in vivo and this was increased by HHcy. We assessed BRB function and retinal morphology using fluorescein angiogram and optical coherence tomography (OCT) under HHcy with and without pharmacological inhibition of NMDAR by (MK801) or in mice lacking endothelial NMDAR (NMDARE-/- mouse). Additionally, retinal albumin leakage and tight junction proteins ZO-1 and occludin were assessed by western blotting analysis. Inhibition or elimination of NMDAR was able to improve the altered retinal hyperpermeability and morphology under HHcy as indicated by significant decrease in retinal albumin leakage and restoration of tight junction proteins ZO-1 and occludin. Our findings underscore a potential role for endothelial NMDAR in mediating Hcy-induced breakdown of BRB and subsequently as a potential therapeutic target in retinal diseases associated with HHcy such as DR and AMD. KEY MESSAGES: • Elevated levels of homocysteine (Hcy) are defined as hyperhomocysteinemia (HHcy). • HHcy is implicated in diabetic retinopathy and age-related macular degeneration. • HHcy alters BRB via activation of N-methyl-D-aspartate receptor.

Diabetic Retinopathy: Mitochondria Caught in a Muddle of Homocysteine

Diabetic retinopathy is one of the most feared complications of diabetes. In addition to the severity of hyperglycemia, systemic factors also play an important role in its development. Another risk factor in the development of diabetic retinopathy is elevated levels of homocysteine, a non-protein amino acid, and hyperglycemia and homocysteine are shown to produce synergistic detrimental effects on the vasculature. Hyperhomocysteinemia is associated with increased oxidative stress, and in the pathogenesis of diabetic retinopathy, oxidative stress-mitochondrial dysfunction precedes the development of histopathology characteristic of diabetic retinopathy. Furthermore, homocysteine biosynthesis from methionine forms S-adenosyl methionine (SAM), and SAM is a co-substrate of DNA methylation. In diabetes, DNA methylation machinery is activated, and mitochondrial DNA (mtDNA) and several genes associated with mitochondrial homeostasis undergo epigenetic modifications. Consequently, high homocysteine, by further affecting methylation of mtDNA and that of genes associated with mtDNA damage and biogenesis, does not give any break to the already damaged mitochondria, and the vicious cycle of free radicals continues. Thus, supplementation of sensible glycemic control with therapies targeting hyperhomocysteinemia could be valuable for diabetic patients to prevent/slow down the development of this sight-threatening disease.

Retinal vein occlusion and chronic kidney disease: A meta-analysis

OBJECTIVES

We performed this meta-analysis to assess the correlation of retinal vein occlusion (RVO) and chronic kidney disease (CKD).

METHODS

We searched PubMed, Embase, Web of Science and Cochrane Library for population-based studies reporting the CKD as associated factor to RVO, central retinal vein occlusion (CRVO) or branch retinal vein occlusion (BRVO). Then we pooled the data for analysis.

RESULTS

After screening potential literature, 12 eligible studies with 23,656,214 individuals were finally included in quantitative synthesis. The pooled prevalence (95% confidence interval [CI]) of CKD in RVO group was 10.9% (95% CI: 6.6%, 15.1%). The pooled prevalence of any RVO in end stage renal disease (ESRD) group was 1.8% (95% CI: 1.6%, 2.1%). The prevalence of CKD was significantly higher in subjects diagnosed with RVO than non-RVO participants (odds ratio [OR]: 3.30; 95% CI: 2.28, 4.76; p < 0.001). CRVO subjects had a higher prevalence of CKD than BRVO patients (OR: 2.17; 95% CI: 1.28, 4.66; p = 0.004). In a similar manner, compared to non-ESRD subjects, ESRD patients had significantly higher prevalence of RVO (OR: 2.19; 95% CI: 1.97, 2.43; p < 0.001), CRVO (OR: 2.61; 95% CI: 2.17, 3.15; p < 0.001) and BRVO (OR: 2.01; 95% CI: 1.76, 2.30; p < 0.001).

CONCLUSION

The prevalence of CKD increases in RVO patients, especially in CRVO. And in turn, the prevalence of RVO also increases in ESRD patients. The data support a correlation of RVO and CKD.

MEK Inhibitor-Associated Central Retinal Vein Occlusion Associated with Hyperhomocysteinemia and MTHFR Variants

Background

Central retinal vein occlusion (CRVO) is a visually threatening event that has rarely been observed in patients taking MEK1/2 inhibitors and that may necessitate permanent discontinuation of a potentially efficacious therapy. We investigated the clinical characteristics of CRVO in patients on mitogen-activated protein kinase kinase (MEK) inhibition to better understand their predisposing factors and clinical course.

Case Series

This was a single-center, retrospective cohort study (between December 2006 and September 2018). Three of 546 patients enrolled in 46 prospective trials involving treatment with MEK inhibitors at Memorial Sloan Kettering Cancer Center were identified as having CRVO. Clinical examination and course, multimodal ophthalmic imaging, and serum laboratory results (including homocysteine levels and genetic variants of methylene tetrahydrofolate reductase [MTHFR]) were reviewed for the 3 affected patients. All 3 patients with MEK inhibitor-associated CRVO had elevated serum homocysteine and gene variants of MTHFR (1 homozygous for A1298C, 1 heterozygous for A1298C, and 1 homozygous for C677T). Following intravitreous injections of anti-VEGF and discontinuation of drug, all patients regained vision to their baseline.

Discussion

MEK inhibitor-associated CRVO is a rare event which can exhibit visual recovery after drug cessation and intravitreous anti-VEGF injections. In this cohort, it was associated with hyperhomocysteinemia and genetic mutations in MTHFR, suggesting a potential role for hyperhomocysteinemia screening prior to initiation of MEK inhibitor therapy.

Hydrogen sulfide intervention in cystathionine-β-synthase mutant mouse helps restore ocular homeostasis

AIM

To investigate the applications of hydrogen sulfide (H₂S) in eye-specific ailments in mice.

METHODS

Heterozygous cystathionine-β-synthase (CBS^+/-) and wild-type C57BL/6J (WT) mice fed with or without high methionine diet (HMD) were administered either phosphate buffered saline (PBS) or the slow-release H₂S donor: GYY4137. Several analyses were performed to study GYY4137 effects by examining retinal lysates for key protein expressions along with plasma glutamate and glutathione estimations. Intraocular pressure (IOP) was monitored during GYY4137 treatment; barium sulfate and bovine serum albumin conjugated fluorescein isothiocyanate (BSA-FITC) angiographies were performed for examining vasculature and its permeability post-treatment. Vision-guided behavior was also tested employing novel object recognition test (NORT) and light-dark box test (LDBT) recordings.

RESULTS

CBS deficiency (CBS^+/-) coupled with HMD led disruption of methionine/homocysteine (Hcy) metabolism leading to hyperhomocysteinemia (HHcy) in CBS^+/- mice as reflected by increased Hcy, and s-adenosylhomocysteine hydrolase (SAHH) levels. Unlike CBS, cystathionine-γ lyase (CSE), methylenetetrahydrofolate reductase (MTHFR) levels which were reduced but compensated by GYY4137 intervention. Heightened oxidative and endoplasmic reticulum (ER) stress responses were mitigated by GYY4137 effects along with enhanced glutathione (GSH) levels. Increased glutamate levels in CBS^+/- strain were prominent than WT mice and these mice also exhibited higher IOP that was lowered by GYY4137 treatment. CBS deficiency also resulted in vision-guided behavioral impairment as revealed by NORT and LDBT findings. Interestingly, GYY4137 was able to improve CBS^+/- mice behavior together with lowering their glutamate levels. Blood-retinal barrier (BRB) appeared compromised in CBS^+/- with vessels' leakage that was mitigated in GYY4137 treated group. This corroborated the results for occludin (an integral plasma membrane protein of the cellular tight junctions) stabilization.

CONCLUSION

Findings reveal that HHcy-induced glutamate excitotoxicity, oxidative damage, ER-stress and vascular permeability alone or together can compromise ocular health and that GYY4137 could serve as a potential therapeutic agent for treating HHcy induced ocular disorders.

Acute retinal vein occlusion and cystic fibrosis

Background

The ocular manifestations of cystic fibrosis typically present with surface irritation or nyctalopia due to Vitamin A deficiency, however, there have been two previous reports of patients with cystic fibrosis that developed retinal vein occlusions. These reports hypothesized that either elevated fibrinogen levels due to chronic infections or elevated homocysteine levels have predisposed patients with cystic fibrosis to develop retinal vein occlusions.

Case presentation

We present a case of a 35-year-old male with cystic fibrosis complicated by chronic sinusitis with no history of organ transplantation or chronic pulmonary infections who presented with an acute branch retinal vein occlusion in his left eye with associated macular edema. Evaluation revealed an elevated fibrinogen level, while the rest of his workup was relatively unremarkable including a normal homocysteine level. His vision remained 20/20 throughout his care and he did not require treatment of his macular edema.

Conclusions

Patients with cystic fibrosis are at an increased risk of developing retinal vein occlusions likely due to a variety of systemic thrombogenic factors rather than a single risk factor which had been reported previously. Elevated fibrinogen levels in these patients may not be due to chronic infections, but inherent to the cystic fibrosis.

The metabolism and significance of homocysteine in nutrition and health

An association between arteriosclerosis and homocysteine (Hcy) was first demonstrated in 1969. Hcy is a sulfur containing amino acid derived from the essential amino acid methionine (Met). Hyperhomocysteinemia (HHcy) was subsequently shown in several age-related pathologies such as osteoporosis, Alzheimer's disease, Parkinson's disease, stroke, and cardiovascular disease (CVD). Also, Hcy is associated with (but not limited to) cancer, aortic aneurysm, hypothyroidism and end renal stage disease to mention some. The circulating levels of Hcy can be increased by defects in enzymes of the metabolism of Met, deficiencies of vitamins B6, B12 and folate or by feeding Met enriched diets. Additionally, some of the pharmaceuticals currently in clinical practice such as lipid lowering, and anti-Parkinsonian drugs are known to elevate Hcy levels. Studies on supplementation with folate, vitamins B6 and B12 have shown reduction in Hcy levels but concomitant reduction in certain associated pathologies have not been definitive. The enormous importance of Hcy in health and disease is illustrated by its prevalence in the medical literature (e.g. > 22,000 publications). Although there are compelling data in favor of Hcy as a modifiable risk factor, the debate regarding the significance of Hcy mediated health effects is still ongoing. Despite associations between increased levels of Hcy with several pathologies being well documented, whether it is a causative factor, or an effect remains inconclusive. The present review though not exhaustive, is focused on several important aspects of Hcy metabolism and their relevance to health.

Retinal vein occlusion and paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disorder associated with increased risk for thrombosis and reduced life expectancy. Retinal vein occlusion (RVO) is a frequent cause of vision loss but its relationship with PNH has not been studied systematically. Patients followed up for RVO in our ophthalmology department were screened for the presence of a PNH clone in peripheral blood by means of flow cytometry. The presence of other well-documented risk factors for RVO was also analyzed. In a series of 110 patients (54 males, median age of 67) we found no evidence of PNH. Most patients (97/110) had cardiovascular risk factors and/or hyperhomocysteinemia (67/110). Inherited thrombophilias were rare (three confirmed cases). Therefore, PNH does not appear to play a role in the development of RVO. However, this finding does not necessarily apply to young patients and/or those with no conventional risk factors for RVO, due to the low number of patients in these subgroups in our population.

Analysis of MTHFR, CBS, Glutathione, Taurine, and Hydrogen Sulfide Levels in Retinas of Hyperhomocysteinemic Mice

Purpose

Hyperhomocysteinemia (Hhcy) is implicated in certain retinal neurovascular diseases, although whether it is causative remains uncertain. In isolated ganglion cells (GCs), mild Hhcy induces profound death, whereas retinal phenotypes in Hhcy mice caused by mutations in remethylation (methylene tetrahydrofolatereductase [Mthfr+/-]) or transsulfuration pathways (cystathionine β-synthase [Cbs+/-]) demonstrate mild GC loss and mild vasculopathy. The current work investigated compensation in vivo of one pathway for the other, and, because the transsulfuration pathway yields cysteine necessary for formation of glutathione (GSH), taurine, and hydrogen sulfide (H2S), they were analyzed also.

Methods

Retinas isolated from wild-type (WT), Mthfr+/-, and Cbs+/- mice (12 and 22 weeks) were analyzed for methylene tetrahydrofolate reductase (MTHFR), cystathionine-β-synthase (CBS), and cystathionase (CTH) RNA/protein levels. Retinas were evaluated for levels of reduced:oxidized GSH (GSH:GSSG), Slc7a11 (xCT), taurine, taurine transporter (TAUT), and H2S.

Results

Aside from decreased CBS RNA/protein levels in Cbs+/- retinas, there were minimal alterations in remethylation/transsulfuration pathways in the two mutant mice strains. Glutathione and taurine levels in Mthfr+/- and Cbs+/- retinas were similar to WT, which may be due to robust levels of xCT and TAUT in mutant retinas. Interestingly, levels of H2S were markedly increased in retinas of Mthfr+/- and Cbs+/- mice compared with WT.

Conclusions

Ganglion cell loss and vasculopathy observed in Mthfr+/- and Cbs+/- mouse retinas may be milder than expected, not because of compensatory increases of enzymes in remethylation/transsulfuration pathways, but because downstream transsulfuration pathway products GSH, taurine, and H2S are maintained at robust levels. Elevation of H2S is particularly intriguing owing to neuroprotective properties reported for this gasotransmitter.

Retinal vein thrombosis: The Internist's role in the etiologic and therapeutic management

Retinal vein occlusion is a common and important cause of vision loss. In general, knowledge about this condition is scant within an internist's practice but the condition is relevant because of its association with other chronic ailments. A diagnosis of RVO should prompt the investigation of conditions needing chronic management in these patients. In this review we summarize the clinical presentation of RVO, its classification, associated risk factors, and treatment focused in the internist's scope of practice.

Homocysteine, methylenetetrahydrofolate reductase C677T polymorphism, and risk of retinal vein occlusion: an updated meta-analysis

Background

To evaluate the role of plasma total homocysteine (tHcy) and homozygosity for the thermolabile variant of the methylenetetrahydrofolate reductase (MTHFR) C677T genotype in the risk of retinal vein occlusion (RVO).

Methods

Relevant studies were selected through an extensive search of PubMed, EMBASE, and the Web of Science databases. Summary weighted mean differences (WMDs) or odds ratios (ORs) and 95% confidence intervals (CI) were calculated with a random-effects model.

Results

Forty-two studies with 6445 participants were included in this updated systematic review and meta-analysis. The mean plasma tHcy level in the RVO patients was significantly higher than in the controls (WMD =2.13 μmol/L; 95% CI: 1.29 to 2.98, P < 0.001), but there was evidence of between-study heterogeneity (P < 0.001). No significant association between MTHFR C677T genotype and RVO was found under all genetic models.

Conclusion

There was some evidence that plasma tHcy is associated with an increased risk of RVO. There was no evidence to suggest an association between homozygosity for the MTHFR C677T genotype and RVO.