Cystathionine Beta-synthase Gene Research Articles

The role of the mitochondrial trans-sulfuration in cerebro-cardio renal dysfunction during trisomy down syndrome.

One in 700 children is born with the down syndrome (DS). In DS, there is an extra copy of X chromosome 21 (trisomy). Interestingly, the chromosome 21 also contains an extra copy of the cystathionine beta synthase (CBS) gene. The CBS activity is known to contribute in mitochondrial sulfur metabolism via trans-sulfuration pathway. We hypothesize that due to an extra copy of the CBS gene there is hyper trans-sulfuration in DS. We believe that understanding the mechanism of hyper trans-sulfuration during DS will be important in improving the quality of DS patients and towards developing new treatment strategies. We know that folic acid "1-carbon" metabolism (FOCM) cycle transfers the "1-carbon" methyl group to DNA (H3K4) via conversion of s-adenosyl methionine (SAM) to s-adenosyl homocysteine (SAH) by DNMTs (the gene writers). The demethylation reaction is carried out by ten-eleven translocation methylcytosine dioxygenases (TETs; the gene erasers) through epigenetics thus turning the genes off/on and opening the chromatin by altering the acetylation/HDAC ratio. The S-adenosyl homocysteine hydrolase (SAHH) hydrolyzes SAH to homocysteine (Hcy) and adenosine. The Hcy is converted to cystathionine, cysteine and hydrogen sulfide (H2S) via CBS/cystathioneγ lyase (CSE)/3-mercaptopyruvate sulfurtransferase (3MST) pathways. Adenosine by deaminase is converted to inosine and then to uric acid. All these molecules remain high in DS patients. H2S is a potent inhibitor of mitochondrial complexes I-IV, and regulated by UCP1. Therefore, decreased UCP1 levels and ATP production can ensue in DS subjects. Interestingly, children born with DS show elevated levels of CBS/CSE/3MST/Superoxide dismutase (SOD)/cystathionine/cysteine/H2S. We opine that increased levels of epigenetic gene writers (DNMTs) and decreased in gene erasers (TETs) activity cause folic acid exhaustion, leading to an increase in trans-sulphuration by CBS/CSE/3MST/SOD pathways. Thus, it is important to determine whether SIRT3 (inhibitor of HDAC3) can decrease the trans-sulfuration activity in DS patients. Since there is an increase in H3K4 and HDAC3 via epigenetics in DS, we propose that sirtuin-3 (Sirt3) may decrease H3K4 and HDAC3 and hence may be able to decrease the trans-sulfuration in DS. It would be worth to determine whether the lactobacillus, a folic acid producing probiotic, mitigates hyper-trans-sulphuration pathway in DS subjects. Further, as we know that in DS patients the folic acid is exhausted due to increase in CBS, Hcy and re-methylation. In this context, we suggest that folic acid producing probiotics such as lactobacillus might be able to improve re-methylation process and hence may help decrease the trans-sulfuration pathway in the DS patients.

Staged, Hybrid Repair Of Bilateral Common Femoral, Profunda, Superficial Femoral, And Popliteal Artery Aneurysms

We report a case of a 69-year-old man with asymptomatic aneurysms of the aorto-ilio-femoropopliteal arteries. CTA showed right side diameters of CFA 3 cm, SFA 2.1 cm, profunda 2.5 cm, popliteal 3.2 cm, and left side CFA 2.6 cm, SFA 2.1 cm, profunda 3.8 cm, popliteal 4.2 cm. Given risk of thrombo-embolic complications, extent of artery disease, and patient preference for limited open surgery, a staged, hybrid approach was utilized. He underwent left-sided bifurcated Dacron interposition graft from the EIA to the SFA and profunda with reimplantation of the largest profunda branch. A Viabahn stent was placed from the SFA anastomosis to P3, sized using IVUS. The right side was addressed seven weeks later with a shorter bifurcated interposition graft from the right EIA to SFA and profunda, with reimplantation of the largest profunda branch. Three branches of the profunda were embolized and a Viabahn stent placed from the profunda anastomosis to a distal target. The popliteal was stented from the SFA anastomosis to P3. Three months post-intervention the left profunda limb thrombosed, though the reimplanted profunda remained patent. He had stable residual endoleaks of the right profunda and bilateral popliteal arteries. He was asymptomatic. Genetic work up showed no pathogenic variants, except for a variant of undetermined significance in the cystathionine beta synthase gene. While optimal management is unclear in such rare pathology, we have found success in short term follow up with a hybrid repair. Patients presenting with this require extensive follow up and multidisciplinary care. View Large Image Figure Viewer Download Hi-res image

Genome-wide identification of cystathionine beta synthase genes in wheat and its relationship with anther male sterility under heat stress.

Cystathionine beta synthase (CBS) domains containing proteins (CDCPs) plays an important role in plant development through regulation of the thioredoxin system, as well as its ability to respond to biotic and abiotic stress conditions. Despite this, no systematic study has examined the wheat CBS gene family and its relation to high temperature-induced male sterility. In this study, 66 CBS family members were identified in the wheat genome, and their gene or protein sequences were used for subsequent analysis. The TaCBS gene family was found to be unevenly distributed on 21 chromosomes, and they were classified into four subgroups according to their gene structure and phylogeny. The results of collinearity analysis showed that there were 25 shared orthologous genes between wheat, rice and Brachypodium distachyon, and one shared orthologous gene between wheat, millet and barley. The cis-regulatory elements of the TaCBS were related to JA, IAA, MYB, etc. GO and KEGG pathway analysis identified these TaCBS genes to be associated with pollination, reproduction, and signaling and cellular processes, respectively. A heatmap of wheat plants based on transcriptome data showed that TaCBS genes were expressed to a higher extent in spikelets relative to other tissues. In addition, 29 putative tae-miRNAs were identified, targeting 41 TaCBS genes. Moreover, qRT-PCR validation of six TaCBS genes indicated their critical role in anther development, as five of them were expressed at lower levels in heat-stressed male sterile anthers than in Normal anthers. Together with anther phenotypes, paraffin sections, starch potassium iodide staining, and qRT-PCR data, we hypothesized that the TaCBS gene has a very important connection with the heat-stressed sterility process in wheat, and these data provide a basis for further insight into their relationship.

MTR, MTRR and CBS Gene Polymorphisms in Recurrent Miscarriages: A Case Control Study from North India.

ABSTRACTBackground:According to various epidemiological studies, the aetiology of recurrent miscarriages (RMs) is multifactorial. The goal of this study is to learn more about the link between genetic polymorphisms and RM.Aim:To evaluate the association of 5-Methytetrahydrofolate-Homocysteine Methyltransferase (MTR) A2756G, 5-Methytetrahydrofolate-Homocysteine Methyltransferase Reductase (MTRR) A66G and cystathionine beta-synthase (CBS) 844INS68 genetic polymorphisms with RM and also to understand the combined effect of the selected genotypes.Study Setting and Design:This was a hospital-based, case–control, observational study.Materials and Methods:A total of 516 participants were recruited in the present study, of which 200 RM cases and 258 controls were included in the present study. Fasting blood sample (~5ml) was drawn from all the participants and were screened for genetic polymorphisms of MTR A2756G, MTRR A66G and CBS 844INS68.Statistical Analysis:The frequency, odd's ratio and Hardy-Weinberg equilibrium were evaluated. SPSS (version 21.0) was used for the data analysis.Results:MTR A2756G genetic polymorphism was not associated with the risk of RM. The ancestral allele of MTRR A66G and the mutant allele of CBS 844INS68 was causing an increased risk of more than two folds for RM. CBS 844INS68 in combination with MTR A2756G was found to pose an increased risk of more than two folds for RM.Conclusion:Genetic polymorphisms particularly MTRR A66G and CBS 844INS68 seems to be elevating the risk and hence making women susceptible for RM.

Identification of three novel pathogenic mutations in cystathionine beta-synthase gene of Pakistani intellectually disabled patients.

Classical homocystinuria (HCU) is an autosomal recessive inborn error of metabolism, which is caused by the cystathionine-β-synthase (CBS: encoded by CBS) deficiency. Symptoms of untreated classical HCU patients include intellectual disability (ID), ectopia lentis and long limbs, along with elevated plasma methionine, and homocysteine. A total of 429 ID patients (age range: 1.6-23 years) were sampled from Northern areas of Punjab, Pakistan. Biochemical and genetic analyses were performed to find classical HCU disease in ID patients. Biochemically, nine patients from seven unrelated families were identified with high levels of plasma methionine and homocysteine. Targeted exonic analysis of CBS confirmed seven causative homozygous mutations; of which three were novel missense mutations (c.451G>T; p.Gly151Trp, c.975G>C; p.Lys325Asn and c.1039+1G>T splicing), and four were recurrent variants (c.451+1G>A; IVS4+1 splicing, c.770C>T; p.Thr257Met, c.808_810del GAG; p.Glu270del and c.752T>C; p.Leu251Pro). Treatment of patients was initiated without further delay with pyridoxine, folic acid, cobalamin, and betaine as well as dietary protein restriction. The immediate impact was noticed in behavioral improvement, decreased irritability, improved black hair color, and socialization. Overall, health outcomes in this disorder depend on the age and symptomatology at the time of treatment initiation. With personalized treatment and care, such patients can reach their full potential of living as healthy a life as possible. This screening study is one of the pioneering initiatives in Pakistan which would help to minimize the burden of such treatable inborn errors of metabolism in the intellectually disabled patients.

Recurrent dislocation of binocular crystal lenses in a patient with cystathionine beta-synthase deficiency

BackgroundEctopia lentis is the common ocular manifestation of homocystinuria resulting from cystathionine beta-synthase (CBS) deficiency which has a high risk of thromboembolic complications.Case presentationThe present study reports the case of a teenager with recurrent lens dislocation and glaucoma. He was diagnosed with CBS deficiency according to a high level of serum homocysteine and compound heterozygous mutations at two different positions on the CBS gene. Antiglaucoma eyedrops and a mydriatic successfully controlled the intraocular pressure, while oral pyridoxine and betaine uptake lowered the serum homocysteine level effectively.ConclusionsChildren with CBS deficiency may suffer from ectopia lentis, glaucoma and/or amblyopia. We firstly discovered a new mutation of CBS c. 697 T > G which had not been reported before. The patient was pyridoxine responsive and well controlled by medicine.

Association of maternal dietary intakes and CBS gene polymorphisms with congenital heart disease in offspring

BackgroundAlthough it is generally acknowledged that genetic and environmental factors are associated with risk of congenital heart disease (CHD), the causes are not fully understood. This study aimed at assessing the association of maternal dietary intakes, genetic variants of cystathionine beta synthase (CBS) gene and their interactions with risk of CHDs in offspring. MethodA hospital-based case-control study of 464 mothers with CHD infants and 504 control mothers of health infant was performed. The exposures of interest were maternal dietary intakes in early pregnancy, single nucleotide polymorphisms (SNPs) of CBS gene. ResultsMore frequent intake of pickled vegetables (adjusted odds ratio[aOR] = 1.81; 95% confidence interval[CI]: 1.38–2.37), smoked foods (aOR = 2.00; 95%CI: 1.53–2.60), barbecued foods (aOR = 1.63; 95%CI: 1.19–2.25) and fried foods (aOR = 1.57; 95%CI: 1.22–2.03) were associated with higher risk of CHD, while salted eggs (aOR = 0.20; 95%CI: 0.12–0.33), fish and shrimp (aOR = 0.34; 95%CI: 0.27–0.44), fresh fruits (aOR = 0.49; 95%CI: 0.37–0.66), and milk products (aOR = 0.54; 95%CI: 0.45–0.65) were associated with lower risk of CHD. The SNPs of CBS gene at rs2851391 (T/T vs C/C: aOR = 1.91, 95%CI: 1.15–3.15) and rs234714 (T/T vs C/C: aOR = 2.22, 95%CI: 1.32–3.73) significantly increased the risk of CHD. Additionally, significant interaction effects between maternal dietary intakes and CBS genetic variants on CHD risks were observed. ConclusionsMaternal dietary factors, CBS genetic variants and their interactions were significantly associated with risk of CHD in offspring. However, it is still unclear how these factors jointly work in the development of CHD, and more studies with larger samples and prospective design are required.

Cystathionine beta synthase regulates mitochondrial dynamics and function in endothelial cells.

Mutations in the human cystathionine beta synthase (CBS) gene are known to cause endothelial dysfunction responsible for cardiovascular and neurovascular diseases. CBS is the predominant hydrogen sulfide (H2 S)-producing enzyme in endothelial cells (ECs). Recently, H2 S was shown to attenuate ROS and improve mitochondrial function. Mitochondria are metabolic organelles that actively transform their ultrastructure to mediate their function. Therefore, we questioned whether perturbation of CBS/H2 S activity could drive mitochondrial dysfunction via mitochondrial dynamics in ECs. Here we demonstrate that silencing CBS induces mitochondria fragmentation, attenuates efficient oxidative phosphorylation, and decreases EC function. Mechanistically, CBS silencing significantly elevates ROS production, thereby leading to reduced mitofusin 2 (MFN2) expression, decouple endoplasmic reticulum-mitochondria contacts, increased mitochondria fission, enhanced receptor-mediated mitophagy, and increased EC death. These defects were significantly rescued by the treatment of H2 S donors. Taken together our data highlights a novel signaling axis that mechanistically links CBS with mitochondrial function and ER-mitochondrial tethering and could be considered as a new therapeutic approach for the intervention of EC dysfunction-related pathologies.

P44 Homocystinuria is a rare cause of fracture in young patients: a case report

Abstract Background Homocysteinuira is a rare autosomal recessive disorder in the metabolism of sulfur-containing aminoacid caused by mutations in the cystathionine beta-synthase gene which encodes the pyridoxine dependent enzyme cystathionine beta-synthase. It is characterised by significant elevations in plasma and urine homocysteine concentrations and fractures. Methods We describe a case of homocysteinuira in a patient who suffered from a low impact patellar fracture, along with a literature review highlighting the critical relationship between homocysteine level and bone health. Results We reported a 36-year-old female with homocysteinuira due to pyridoxine (B6) unresponsive severe Cystathionine Beta-Synthase deficiency. She developed a right patellar low-impact fracture with osteopenia on X-ray. Examination revealed severe scoliosis with bilateral aphakia (absence of the lens of the eye). Her labs showed, persistent high homocysteine above 100 umol/L (4-10), methionine 383 umol/L (10-42), vitamin D 12 ng/ml. Her spine X-ray revealed severe scoliosis with osteopenia but no fracture. Her DXA scan showed her Z-Score was within the expected range for her age in hip, spine and 1/3 radius areas, however her ultra-distal radius Z-Score was -4.0. Her homocysteine level was mostly higher than 100 due to non-compliance with dietary advice and treatment. The severity of complications primarily depends on the age at diagnosis and the residual cystathionine beta-synthase activity. Most homocysteinuira patients diagnosed in adulthood have severe osteoporosis. Notably, a thinning and lengthening of the long bones result in tall and thin individuals with an appearance like that of Marfan’s syndrome. However, osteoporosis, particularly of the spine, which is associated with scoliosis, is one of the distinguishing features of the disease. High homocysteine levels in homocysteinuric patients impair the function of bone cells that regulate bone remodeling as well as bone material properties such as collagen cross-linking. This imbalance between bone formation and resorption may lead to a low BMD and fracture in patients with. Interestingly, even in general population hyperhomocysteinemia with a plasma level of more than > 13 nmol/ml has been found to be associated with low BMD and an increased risk of fractures that is independent of BMD. Deficiencies in vitamin B6, B12, or folate can lead to increased serum levels of homocysteine as these vitamins act as co-factors for various enzymes involved in homocysteine metabolism. This can be easily rectified with dietary intervention. Conclusion In young patients with a fracture or low BMD, hyperhomocysteinemia could play an important role in the pathogenesis. Homocysteine level should be included in the work up for secondary osteoporosis at young age-group. Simple dietary measures and vitamin B6, folate and B12 supplement should be considered as adjuvant therapeutic option for lowm BMD patients if deficient. Possibly the BMD of the ultra-distal radius is the most sensitive to detect bone changes in hyperhomocysteinemic patients. Disclosures A. Al-Allaf None. T. Paul None. B. Awadh None.

The Spectrum of Mutations of Homocystinuria in the MENA Region

Homocystinuria is an inborn error of metabolism due to the deficiency in cystathionine beta-synthase (CBS) enzyme activity. It leads to the elevation of both homocysteine and methionine levels in the blood and urine. Consequently, this build-up could lead to several complications such as nearsightedness, dislocated eye lenses, a variety of psychiatric and behavioral disorders, as well as vascular system complications. The prevalence of homocystinuria is around 1/200,000 births worldwide. However, its prevalence in the Gulf region, notably Qatar, is exceptionally high and reached 1:1800. To date, more than 191 pathogenic CBS mutations have been documented. The majority of these mutations were identified in Caucasians of European ancestry, whereas only a few mutations from African-Americans or Asians were reported. Approximately 87% of all CBS mutations are missense and do not target the CBS catalytic site, but rather result in unstable misfolded proteins lacking the normal biological function, designating them for degradation. The early detection of homocystinuria along with low protein and methionine-restricted diet is the best treatment approach for all types of homocystinuria patients. Yet, less than 50% of affected individuals show a significant reduction in plasma homocysteine levels after treatment. Patients who fail to lower the elevated homocysteine levels, through high protein-restricted diet or by B6 and folic acid supplements, are at higher risk for cardiovascular diseases, neurodegenerative diseases, neural tube defects, and other severe clinical complications. This review aims to examine the mutations spectrum of the CBS gene, the disease management, as well as the current and potential treatment approaches with a greater emphasis on studies reported in the Middle East and North Africa (MENA) region.

An eQTL in the cystathionine beta synthase gene is linked to osteoporosis in laying hens

BackgroundSkeletal damage is a challenge for laying hens because the physiological adaptations required for egg laying make them susceptible to osteoporosis. Previously, we showed that genetic factors explain 40% of the variation in end of lay bone quality and we detected a quantitative trait locus (QTL) of large effect on chicken chromosome 1. The aim of this study was to combine data from the commercial founder White Leghorn population and the F2 mapping population to fine-map this QTL and understand its function in terms of gene expression and physiology.ResultsSeveral single nucleotide polymorphisms on chromosome 1 between 104 and 110 Mb (galGal6) had highly significant associations with tibial breaking strength. The alternative genotypes of markers of large effect that flanked the region had tibial breaking strengths of 200.4 vs. 218.1 Newton (P < 0.002) and, in a subsequent founder generation, the higher breaking strength genotype was again associated with higher breaking strength. In a subsequent generation, cortical bone density and volume were increased in individuals with the better bone genotype but with significantly reduced medullary bone quality. The effects on cortical bone density were confirmed in a further generation and was accompanied by increased mineral maturity of the cortical bone as measured by infrared spectrometry and there was evidence of better collagen cross-linking in the cortical bone. Comparing the transcriptome of the tibia from individuals with good or poor bone quality genotypes indicated four differentially-expressed genes at the locus, one gene, cystathionine beta synthase (CBS), having a nine-fold higher expression in the genotype for low bone quality. The mechanism was cis-acting and although there was an amino-acid difference in the CBS protein between the genotypes, there was no difference in the activity of the enzyme. Plasma homocysteine concentration, the substrate of CBS, was higher in the poor bone quality genotype.ConclusionsValidated markers that predict bone strength have been defined for selective breeding and a gene was identified that may suggest alternative ways to improve bone health in addition to genetic selection. The identification of how genetic variants affect different aspects of bone turnover shows potential for translational medicine.

Estimated prevalence of moderate to severely elevated total homocysteine levels in the United States: A missed opportunity for diagnosis of homocystinuria?

Classical homocystinuria (HCU) is a genetic disorder caused by mutations in the cystathionine beta synthase gene, which results in impaired metabolism of the sulfur-bearing amino acid homocysteine and its accumulation in blood and tissues. Classical HCU can be detected via newborn screening in the United States, but the test is widely acknowledged to miss many patients. While severely elevated homocysteine levels (>100 μmol /L) frequently lead to a classical HCU diagnosis, intermediate levels (>30 to 100 μmol /L), though linked to many of the known complications of HCU, are not always recognized as associated with HCU. We aimed to identify and describe potentially undiagnosed classical HCU patients using a nationally-representative database of administrative claims and laboratory results. We estimated the national prevalence of patients with homocysteine >30 μmol /L, and compared their demographic and clinical characteristics to those of patients with homocysteine levels ≤30 μmol/L. Among 57,580 patients with a homocysteine test result, 1.8% had a value >30 μmol /L. Patients with homocysteine >30 μmol /L were more frequently diagnosed with hypothyroidism (39.2% vs. 20.7%, p < .001) and renal disease (9.7% vs. 5.5%, p < .001), and were more likely to have a prescription for an anxiolytic/antidepressant (44.5% vs. 38.9%), opioid (58.4% vs. 53.1%), steroid (46.4% vs. 42.5%), or thyroid hormone (38.8% vs. 18.8%), compared to patients with homocysteine ≤30 μmol /L (all p < .05). Both groups were equally likely to have a diagnosis of homocystinuria or another disorder of sulfur-bearing amino acid metabolism (3.8% vs. 4.0%, p = .752). The age-adjusted national prevalence of homocysteine >30 μmol /L was estimated at 33,068 (95% CI: 1033 - 35,104). These findings suggest that thousands of people in the US may be living with intermediate to severely elevated homocysteine levels and may require further evaluation for the presence of classical HCU.

A proactive genotype-to-patient-phenotype map for cystathionine beta-synthase

BackgroundFor the majority of rare clinical missense variants, pathogenicity status cannot currently be classified. Classical homocystinuria, characterized by elevated homocysteine in plasma and urine, is caused by variants in the cystathionine beta-synthase (CBS) gene, most of which are rare. With early detection, existing therapies are highly effective.MethodsDamaging CBS variants can be detected based on their failure to restore growth in yeast cells lacking the yeast ortholog CYS4. This assay has only been applied reactively, after first observing a variant in patients. Using saturation codon-mutagenesis, en masse growth selection, and sequencing, we generated a comprehensive, proactive map of CBS missense variant function.ResultsOur CBS variant effect map far exceeds the performance of computational predictors of disease variants. Map scores correlated strongly with both disease severity (Spearman’s ϱ = 0.9) and human clinical response to vitamin B6 (ϱ = 0.93).ConclusionsWe demonstrate that highly multiplexed cell-based assays can yield proactive maps of variant function and patient response to therapy, even for rare variants not previously seen in the clinic.

CBS gene polymorphism and promoter methylation-mediating effects on the efficacy of folate therapy in patients with hyperhomocysteinemia.

A decrease in cystathionine beta-synthase (CBS) enzyme activity could lead to hyperhomocysteinemia (HHcy). Studies have revealed that DNA methylation has a mediating effect on the development of diseases. The present study aimed to explore CBS promoter methylation-mediating effects on the efficacy of folate treatment for HHcy. HHcy patients were treated with folate (5 mg/day) for 90 days and then divided into a failure group (Hcy ≥ 15 μmol/l) and a success group (Hcy < 15 μmol/l) according to post-treatment plasma Hcy levels. Genotyping of CBS gene (rs2851391 and rs706209) in patients (n = 638) was detected using a MassArray system (Sequenom, San Diego, CA, USA). The baseline DNA methylation levels of patients (n = 299) were detected using MethylTarget™ technology (Genesky Biotechnologies Inc., Shanghai, China). The CBS rs2851391 TC + CC genotype was related to a 57% reduction of failure risk in HHcy treatment compared to the TT genotype (95% confidence interval [CI] = 0.19-0.97). The CBS rs706209 CT + TT genotype had a 2.97-fold increased risk of failure to treatment compared to the CC genotype (95% CI = 1.52-5.80). After adjustment for confounding factors, the odds ratio (95% CI) for the risk of failure in HHcy treatment in total and male patients was 0.55 (0.32-0.93) and 0.34 (0.16-0.69), respectively, for patients with higher methylation levels (≥ methylation median). Additionally, baseline CBS promoter methylation mediated 33.39% of the effect of rs2851391 on the efficacy of folate treatment for HHcy (ACME [average causal mediation effects]: -0.05, 95% CI = -0.11 to 0.00, p = 0.046). The present study indicates that CBS gene polymorphism and promoter methylation could affect the efficacy of HHcy. There were potentially causal effects of genetic, epigenetic variations at the CBS rs2851391 locus on the efficacy of HHcy therapy with folate.

Homocystinuria a rare cause of low BMD in young patients: A case report with literature review

Background: Homocystinuira is a rare autosomal recessive disorder in the metabolism of sulfur-containing amino acid caused by mutations in the cystathionine beta-synthase gene which encodes the pyridoxine (Vitamin B6) dependent enzyme cystathionine beta-synthase. It is characterized by significant elevations in plasma and urine homocysteine concentrations, which could be associated with increased risk of fracture. Methods: We describe a case of Homocystinuria who suffered from a low impact patellar fracture with a literature review to highlight the critical relationship between homocysteine level and bone health. Results: We reported a 36-year-old female with a diagnosis of Homocystinuria due to pyridoxine (B6) unresponsive severe Cystathionine Beta-Synthase deficiency. After a minor knee injury she developed a right patellar fracture and her X-ray revealed osteopenia. On examination, she has severe scoliosis in the spine with bilateral aphakia (absence of the lens of the eye). Her labs showed, persistent high Homocysteine above 100 umol/L, Methionine: 383 umol/L (10-42), Vitamin D 12 ng/ml. Her spine X-ray revealed very severe scoliosis with osteopenia but no vertebra fracture. Her DXA scan showed her Z-Score was within the expected range for her age in hip, spine and 1/3 radius areas, however her ultra-distal radius Z-Score was -4.0. Her Homocystine level was mostly higher than 100 due to non-compliance with dietary advice and treatment. High homocysteine levels in Homocystinuric patients impair the function of bone cells that regulate bone remodeling as well as bone material properties such as collagen cross-linking. This imbalance between bone formation and resorption may lead to a low BMD and fracture in patients with homocystinuria. Interestingly, even in general population hyperhomocystinemia with a plasma level of more than > 13 nmol/ml has been found to be associated with low BMD and an increased risk of fractures that is independent of BMD. Deficiencies in vitamin B6, B12, or folate can lead to increased serum levels of Homocysteine as these vitamins act as co-factors for various enzymes involved in homocysteine metabolism. This can be easily rectified with dietary intervention. Conclusion: In young patients with a fracture or low bone mineral density, hyperhomocystinemia could play an important role in the pathogenesis. This should be included in the work up for secondary causes for osteoporosis for this age-group. Simple dietary measures and vitamin B6, folate and B12 supplement should be considered as adjuvant therapeutic option for any patient with osteoporosis and fractures, if deficient. Possibly the BMD of the ultra-distal radius is the most sensitive to detect bone changes in these patients.

Ocular manifestations of homocystinuria due to cystathionine beta-synthase deficiency: A rare case report with genetic analysis

Microspherophakia is a developmental lens anomaly characterized by increased anteroposterior diameter and reduced equatorial diameter, which predisposes to secondary glaucoma. A 12-year-old boy presented with diminution of vision. Slit-lamp examination showed anteriorly dislocated crystalline lens. Blood analysis revealed elevated homocysteine levels. Genetic analysis showed cystathionine beta-synthase gene mutation, thus confirming the diagnosis of homocystinuria. To prevent secondary glaucoma, the patient was taken up for surgical intervention. This report highlights a case of homocystinuria with microspherophakia diagnosed with the help of genetic testing.

Analysis of the Qatari R336C cystathionine β-synthase protein in mice.

Classical homocystinuria is a recessive inborn error of metabolism caused by mutations in the cystathionine beta-synthase (CBS) gene. The highest incidence of CBS deficiency in the world is found in the country of Qatar due to the combination of high rates of consanguinity and the presence of a founder mutation, c.1006C>T (p.R336C). This mutation does not respond to pyridoxine and is considered severe. Here we describe the creation of a mouse that is null for the mouse Cbs gene and expresses human p.R336C CBS from a zinc-inducible transgene (Tg-R336C Cbs -/- ). Zinc-treated Tg-R336C Cbs -/- mice have extreme elevation in both serum total homocysteine (tHcy) and liver tHcy compared with control transgenic mice. Both the steady-state protein levels and CBS enzyme activity levels in liver lysates from Tg-R336C Cbs -/- mice are significantly reduced compared to that found in Tg-hCBS Cbs -/- mice expressing wild-type human CBS. Treatment of Tg-R336C Cbs -/- mice with the proteasome inhibitor bortezomib results in stabilization of liver CBS protein and an increase in activity to levels found in corresponding Tg-hCBS Cbs -/- wild type mice. Surprisingly, serum tHcy did not fully correct even though liver enzyme activity was as high as control animals. This discrepancy is explained by in vitro enzymatic studies of mouse liver extracts showing that p.R336C causes reduced binding affinity for the substrate serine by almost 7-fold and significantly increased dependence on pyridoxal phosphate in the reaction buffer. These studies demonstrate that the p.R336C alteration effects both protein stability and substrate/cofactor binding.

Short tandem repeats and methylation in the promoter region affect expression of cystathionine beta-synthase gene in the laying hen

Homocysteine can be converted to cysteine via the transsulfuration pathway where cystathionine beta-synthase (CBS) is a rate-limiting enzyme. Homocysteine is thought to play a role in bone remodelling and strength. Previous results indicated that some of the difference in bone strength of end-of-lay hens may be associated with CBS expression level. To investigate if differences in the promoter region of the CBS gene might be responsible for observed differences in gene expression between CBS alleles post mortem- and in-vitro expression studies have been undertaken. Transfection of the DF-1 avian cell line with a series of deletion fragments of the 5′ promoter, or constructs containing three CBS allele sequences, with a luciferase reporter revealed that a core region of −155 to +131 bp in the CBS promoter was essential for mRNA expression. We found that a variable number of short tandem repeats (7 nucleotide motif and 6 nucleotide repeats) in the core region of the promoter affecting the transcriptional activity and a strong effect for gene expression. However, methylation of the 6 nucleotide repeats varied between allelic variants and these maybe responsible for differences in promoter activity. Our findings indicated variable short tandem repeats and the differentially methylated sites in the promoter region may be responsible for CBS expression differences in the bone of laying hens.

WITHDRAWN: Short tandem repeats and methylation in the promoter region affect expression of cystathionine beta-synthase gene in the laying hen

WITHDRAWN: Short tandem repeats and methylation in the promoter region affect expression of cystathionine beta-synthase gene in the laying hen

Homocystinuria due to cystathionine beta-synthase (CBS) deficiency in Russia: Molecular and clinical characterization

We present the results of the 45-year clinical observation of 27 Russian homocystinuria patients. We made a mutation analysis of the CBS gene for thirteen patients from eleven unrelated genealogies. All patients except for the two were compound heterozygotes for the mutations detected. The most frequent mutation in the cohort investigated was splice mutation IVS11-2a->c. We detected one new nonsense mutation, one new missense-mutation and three novel small deletions. We also report the clinical case of the B6-responsive patient genotyped as Ile278Thr/Cys109Arg.