Transcobalamin deficiency - a rare genetic defect in transportation of cobalamin; case report.

BACKGROUND: Vitamin B12 is primarily transported from plasma to cells by Transcobalamin. Deficiency of Transcobalamin is a rare autosomal recessive disorder that results in unavailability of cobalamin in cells and accumulation of homocysteine and methylmalonic acid. CASE REPORT: We report a case of a 2-year-old male child with persistent pancytopenia, recurrent infections, and megaloblastic anemia. Next-generation sequencing identified a novel variant in exon 8 of TCN2 gene. Substantial improvement has been observed following administration of high doses of parenteral methylcobalamin. CONCLUSION: In patients with unresolved pancytopenia and megaloblastic anemia, Transcobalamin deficiency should be investigated and treated promptly to prevent any irreversible and harmful outcome.

A novel TCN2 mutation with unusual clinical manifestations of hemolytic crisis and unexplained metabolic acidosis: expanding the genotype and phenotype of transcobalamin II deficiency.

BACKGROUND: Transcobalamin deficiency is a rare inborn metabolic disorder, characterized by pancytopenia, megaloblastic anemia, failure to thrive, diarrhea, and psychomotor retardation. CASE PRESENTATION: We describe a patient who first presented at 3 months of age, with pancytopenia, hepatosplenomegaly, recurrent infection, metabolic acidosis, and acute hemolytic crisis. Extensive hematologic and immunologic investigations did not identify inherited bone marrow failure syndrome, acute leukemia or its related disorders. Whole exome sequencing identified a novel homozygous TCN2 mutation, c.428-2A > G and mRNA study confirmed an aberrant transcription of exon 4 skipping. The mutant protein is predicted to have an in-fame 51 amino acids deletion (NP_000346:p.Gly143_Val193del). The patient exhibited marked clinical improvement following hydroxocobalamin treatment. CONCLUSIONS: Transcobalamin deficiency should be investigated in infants with unexplained pancytopenia and acute hemolytic crisis with or without typical evidence of vitamin B12 deficiency.

Vitamin B12 may play a preventive role in esophageal precancerous lesions: a case-control study based on markers in blood and 3-day duplicate diet samples.

PURPOSE: It is hypothesized that vitamin B12 may prevent tumor initiation during the early stage of carcinogenesis such as esophageal precancerous lesions (EPL), whereas an excessive level may promote tumor progression during the later stages of carcinogenesis. This study aimed to determine the role of vitamin B12 in EPL by detecting vitamin B12-related markers in both blood and diet. METHODS: This case-control study based on 3-day duplicated diet samples was conducted in a high-risk area of Huai'an, China. A 100 EPL cases and 100 healthy controls matched by gender, age (± 2 years) and villages were included. Dietary intake of vitamin B12 and cobalt, plasma cobalt level, the serum levels of vitamin B12 and transcobalamin II (TC II) were quantitatively analyzed. RESULTS: Dietary vitamin B12 intake (p for trend = 0.384) and plasma cobalt level (p for trend = 0.253) were not associated with EPL risk, but high dietary cobalt intake (p for trend = 0.034), increased serum levels of vitamin B12 (p for trend = 0.036) and TC II (p for trend < 0.001) were significantly associated with the reduced EPL risk. However, the significant negative association between dietary cobalt intake, plasma cobalt level or serum vitamin B12 level and EPL was only found in female or male subjects. CONCLUSION: Excellent transport capability of bio-active vitamin B12 in vivo and adequate levels of vitamin B12 and cobalt may play preventive roles in EPL. Additionally, the association between vitamin B12, cobalt and the risk of EPL may vary in different genders.

Intracellular and Tissue Levels of Vitamin B12 in Hepatocytes Are Modulated by CD320 Receptor and TCN2 Transporter.

The liver mass constitutes hepatocytes expressing receptors for vitamin B12 (B12)-bound transporters in circulation. However, intrahepatic and circulating B12 interrelationship levels remain unclear. We assessed the intracellular B12 levels at various circulating B12 concentrations in human HepG2 cell-line and liver tissue levels of B12 in the C57BL/6 mouse model. In HepG2 cells treated with a range of B12 concentrations, the intracellular and circulatory B12 levels, transcript and protein levels of B12 receptor (CD320) and transporter (TCN2) were determined using immunoassays, qRT-PCR and Western blot, respectively. Similar assessments were done in plasma and liver tissue of C57BL/6 mice, previously fed a diet of either a high or low B12 (30.82 µg B12/kg and 7.49 µg B12/kg, respectively) for 8-10 weeks. The physiological B12 status (0.15-1 nM) resulted in increased levels of intracellular B12 in HepG2 cells compared to supraphysiological levels of B12 (>1 nM). Gene and protein expression of CD320 and TCN2 were also higher at physiological levels of B12. Progressively increasing extracellular B12 to supraphysiological levels led to relative decreased levels of intracellular B12, lower expression of gene and protein levels of CD320 and TCN2. Similar results were observed in liver tissue from mice fed on a low B12 diet verses high B12 diet. These findings suggest that unlike supraphysiological B12, physiological levels of B12 in the extracellular media or circulation accelerates active transport of B12, and expression of CD320 and TCN2, resulting in higher relative uptake of B12 in hepatocytes.

Biological Activity of Pseudovitamin B12 on Cobalamin-Dependent Methylmalonyl-CoA Mutase and Methionine Synthase in Mammalian Cultured COS-7 Cells.

Adenyl cobamide (commonly known as pseudovitamin B12) is synthesized by intestinal bacteria or ingested from edible cyanobacteria. The effect of pseudovitamin B12 on the activities of cobalamin-dependent enzymes in mammalian cells has not been studied well. This study was conducted to investigate the effects of pseudovitamin B12 on the activities of the mammalian vitamin B12-dependent enzymes methionine synthase and methylmalonyl-CoA mutase in cultured mammalian COS-7 cells to determine whether pseudovitamin B12 functions as an inhibitor or a cofactor of these enzymes. Although the hydoroxo form of pseudovitamin B12 functions as a coenzyme for methionine synthase in cultured cells, pseudovitamin B12 does not activate the translation of methionine synthase, unlike the hydroxo form of vitamin B12 does. In the second enzymatic reaction, the adenosyl form of pseudovitamin B12 did not function as a coenzyme or an inhibitor of methylmalonyl-CoA mutase. Experiments on the cellular uptake were conducted with human transcobalamin II and suggested that treatment with a substantial amount of pseudovitamin B12 might inhibit transcobalamin II-mediated absorption of a physiological trace concentration of vitamin B12 present in the medium.

Genetic polymorphisms of the cobalamin transport system are associated with idiopathic recurrent implantation failure.

PURPOSE: Vitamin B12 (cobalamin, Cbl) plays a role in the recycling of folate, which is important in pregnancy. Transcobalamin II (TCN2) and transcobalamin receptor (TCblR) proteins are involved in the cellular uptake of Cbl. TCN2 binds Cbl in the plasma, and TCblR binds TCN2-Cbl at the cell surface. Therefore, we investigated the potential association between polymorphisms in Cbl transport proteins, TCN2 and TCblR, and recurrent implantation failure (RIF) susceptibility. METHODS: The genotypes of TCN2 67A>G, TCN2 776C>G, and TCblR 1104C>T were determined for RIF patients and healthy controls using a polymerase chain reaction restriction fragment length polymorphism assay. Additionally, statistical analysis was performed to compare the genotype frequencies between RIF patients and controls. RESULTS: The TCN2 67 polymorphism AG type was associated with RIF risk. Some allele combinations that contained the TCN2 67 polymorphism G allele were associated with increased RIF risk, whereas other allele combinations that contained the TCblR 1104 polymorphism T alleles were associated with decreased RIF risk. In genotype combination analysis, two combinations containing the TCN2 67 polymorphism AG type were associated with RIF risk. CONCLUSION: Our study showed that the polymorphisms of TCN2 and TCblR are associated with RIF and are potential genetic predisposing factors for RIF among Korean women. Additionally, our findings support a potential role for TCN2 and TCblR in RIF among Korean women. However, further studies are required to investigate the role of the polymorphisms in those proteins and RIF because the roles of the TCN2 and TCblR polymorphisms in RIF are not clear.

Investigation of Receptor-Mediated Cyanocobalamin (Vitamin B12) Transport across the Inner Blood-Retinal Barrier Using Fluorescence-Labeled Cyanocobalamin.

The blood-to-retina supply of cyanocobalamin (vitamin B12) across the blood-retinal barrier (BRB) was investigated by synthesizing a fluorescence-labeled cyanocobalamin (Cy5-cyanocobalamin). In the in vivo analysis following internal jugular injection of Cy5-cyanocobalamin, confocal microscopy showed the distribution of Cy5-cyanocobalamin in the inner plexiform layer (IPL), the outer plexiform layer (OPL), and the retinal pigment epithelium (RPE). In the in vitro analysis with TR-iBRB2 cells, an in vitro model cell line of the inner BRB, Cy5-cyanocobalamin uptake by TR-iBRB2 cells exhibited a time-dependent increase after preincubation with transcobalamin II (TCII) protein, during its residual uptake without preincubation with TCII protein. The Cy5-cyanocobalamin uptake by TR-iBRB2 cells was significantly reduced in the presence of unlabeled cyanocobalamin, chlorpromazine, and chloroquine and was also significantly reduced under Ca2+-free conditions. Confocal microscopy of the TR-iBRB2 cells showed fluorescence signals of Cy5-cyanocobalamin and GFP-TCII protein, and these signals merged with each other. The RT-PCR, Western blot, and immunohistochemistry clearly suggested the expression of TCII receptor (TCII-R) in the inner and outer BRB. These results suggested the involvement of receptor-mediated endocytosis in the blood-to-retina transport of cyanocobalamin at the inner BRB with implying its possible involvement at the outer BRB.

Evaluation of transcobalamin II rs1801198 and transcobalamin II receptor rs2336573 gene polymorphisms in recurrent spontaneous abortion.

It has been proposed that transcobalamin 2 (TCN2) and the transcobalamin 2 receptor (TCN2R) are associated with idiopathic recurrent spontaneous abortion (RSA). The aim of the present study was to investigate the impact of TCN2 rs1801198 and TCN2R rs2336573 polymorphism on RSA in a sample of Iranian population. This case-control study was done on 92 RSA patients and 93 normal, fertile women. Genotyping of the TCN2 rs1801198 and TCN2R rs2336573 variants was done by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP). The findings showed no significant association between the TCN2 rs1801198 and TCN2R rs2336573 polymorphisms and the risk/protection of RSA. Our results did not support an association between the TCN2 polymorphism and the risk of RSA in a sample of southeast Iranian population. Larger studies with different ethnicities are needed to evaluate the possible impact of TCN2 and TCN2R polymorphisms on the pathogenesis of RSA. Impact statement What is already known on this subject? Recurrent spontaneous abortion (RSA), a multifactorial condition, is one of the most common complications of pregnancy. It has been proposed that genetic polymorphisms play a role in the pathogenesis of RSA. Few studies have examined the association between TNC2 and TCN2R polymorphisms and the RSA risk and the findings were inconsistent. The aim of the current study was to determine the possible association between the TCN2 rs1801198 and TCN2R rs2336573 polymorphisms and the RSA in a sample of the southeast Iranian population. What do the results of the study add? The findings of the present case-control study did not support an association between the TCN2 rs1801198 and TCN2R rs2336573 polymorphisms and the risk of RSA in a sample of the Iranian population. What are the implications of these findings for clinical practice and future research? The findings of this study may provide a basis for future studies with larger sample sizes and different ethnicities on the role of TCN2 and TCN2R polymorphisms in the pathogenesis of RSA.

Association of ulcerative colitis with transcobalamin II gene polymorphisms and serum homocysteine, vitamin B12, and folate levels in Chinese patients.

It has been reported that abnormal elevation of homocysteine is quite prevalent in ulcerative colitis (UC) patients. We attempted to explore the relationship of UC with transcobalamin II (TCN2) gene polymorphisms and serum homocysteine, vitamin B12, and folate levels in Chinese patients. TCN2 (rs1801198, rs9606756) genotypes were detected by the improved multiple ligase detection reaction (iMLDR) technique in 527 UC patients and 574 controls. Moreover, 128 UC patients and 138 controls were randomly selected for the measurement of homocysteine, vitamin B12, and folate levels by enzymatic cycling assay or chemiluminescence immunoassay. For TCN2 (rs1801198), the frequency of allele G and combined frequencies of CG and GG genotypes were increased in patients with mild, moderate, and severe UC compared with those with remission UC (all P < 0.001). The average homocysteine level was elevated (10.78 ± 3.33 vs 9.91 ± 2.88 µmol/L, P = 0.024), whereas the average vitamin B12 and folate levels were reduced (408.66 ± 185.00 vs 457.42 ± 206.47 pg/mL, P = 0.044; 6.81 ± 3.06 vs 8.17 ± 2.58 ng/mL, P < 0.001, respectively) in UC patients than in controls. Compared with controls, the prevalence of hyperhomocysteinemia (HHcy >15.0 µmol/L), vitamin B12 deficiency (<203.0 pg/mL), and folate deficiency (<4.0 ng/mL) was higher in UC patients (all P < 0.05). Both HHcy and folate deficiency were shown to be independent risk factors for UC (95% CI = 1.206-12.293, P = 0.023; 95% CI = 1.910-11.129, P = 0.001, respectively). TCN2 (rs1801198, rs9606756) mutations might aggravate the severity of UC. HHcy and folate deficiency are independent risk factors for UC.

New data supporting that early diagnosis and treatment are possible and necessary in intracellular cobalamin depletion: the case of transcobalamin II deficiency.

OBJECTIVES: Transcobalamin II (TC) promotes the cellular uptake of cobalamin (Cbl) through receptor-mediated endocytosis of the TC-cbl complex in peripheral tissues. TC deficiency is a rare disorder that causes intracellular Cbl depletion. It presents in early infancy with a failure to thrive, diarrhea, anemia, agammaglobulinemia, and pancytopenia. Data from five TC-deficient patients including clinical, biochemical, and molecular findings, as well as long-term outcomes, were collected. CASE PRESENTATION: Mutation analysis revealed one unreported pathogenic variant in the TCN2 gene. One patient had exocrine pancreatic insufficiency. We conducted a retrospective analysis of C3 and C3/C2 from dried blood samples, as this is implemented for newborn screening (NBS). We detected a marked increase in the C3/C2 ratio in two samples. Treatment was based on parenteral Cbl. Three patients treated before six months of age had an initial favorable outcome, whereas the two treated later or inadequately had neurological impairment. CONCLUSIONS: This is the first report of Argentinean patients with TC deficiency that detected a new variant in TCN2. NBS may be a tool for the early detection of TC deficiency. This data emphasizes that TC deficiency is a severe disorder that requires early detection and long-term, aggressive therapy. Accurate diagnosis is imperative, because early detection and treatment can be life-saving.

Transcobalamin 2 orchestrates monocyte proliferation and TLR4-driven inflammation in systemic lupus erythematosus via folate one-carbon metabolism.

Background: SLE is a complex autoimmune disease with deleterious effects on various organs. Accumulating evidence has shown abnormal vitamin B12 and one-carbon flux contribute to immune dysfunction. Transcobalamin II (TCN2) belongs to the vitamin B12-binding protein family responsible for the cellular uptake of vitamin B12. The role of TCN2 in SLE is still unclear. Methods: We collected clinical information and blood from 51 patients with SLE and 28 healthy controls. RNA sequencing analysis, qPCR, and western blot confirmed the alteration of TCN2 in disease monocytes. The correlation between TCN2 expression and clinical features and serological abnormalities was analyzed. TCN2 heterozygous knockout THP1 cells were used to explore the effects of TCN2 dysfunction on monocytes. CCK-8 assay and EdU staining were used to detect cell proliferation. ELISA was conducted to assess vitamin B12, glutathione, and cytokines changes. UHPLC-MRM-MS/MS was used to detect changes in the intermediates of the one-carbon cycle. Flow cytometry is used to detect cell cycle, ROS, mitoROS, and CD14 changes. Results: Elevated TCN2 in monocytes was correlated positively with disease progression and specific tissue injuries. Using CD14+ monocytes and TCN2 genetically modified THP1 cell lines, we found that the TCN2 was induced by LPS in serum from SLE patients. TCN2 heterozygous knockout inhibited cellular vitamin B12 uptake and one-carbon metabolism, leading to cell proliferation arrest and decreased Toll-like receptor 4 (TLR4)-mediated CCL2 release. Methionine cycle metabolites, s-adenosylmethionine and homocysteine, rescued these effects, whereas folate treatment proved to be ineffective. Folate deficiency also failed to replicate the impact of TCN2 downregulation on THP1 inflammatory response. Conclusion: Our study elucidated the unique involvement of TCN2-driven one-carbon flux on SLE-associated monocyte behavior. Increased TCN2 may promote disease progression and tissue damage by enhancing one-carbon flux, fostering monocyte proliferation, and exacerbating TLR4 mediated inflammatory responses. The inhibition of TCN2 may be a promising therapeutic approach to ameliorate SLE.

"Progressive myoclonic ataxia and developmental/epileptic encephalopathy associated with a novel homozygous mutation in TCN2 gene".

BACKGROUND: Transcobalamin II (TCN2) defect is a rare metabolic disorder associated with a range of neurological manifestations, including mild developmental delay, severe intellectual disability, ataxia, and, in some cases, seizures. Cobalamin, an essential nutrient, plays a crucial role in central nervous system myelination. CLINICAL PRESENTATION: We present a family with an index patient who exhibited progressive neurodevelopmental regression starting at 9 months of age, accompanied by myoclonic seizures, ataxia, and tremor. No significant hematological abnormalities were observed. Exome sequencing analysis identified a novel homozygous mutation, c.3G>A - P(Met1I), affecting the acceptor site of intron 4 of the TCN2 gene (chromosome 22: 31003321, NM_000355.4), leading to likely pathogenic variant potentially affecting translation. Following treatment with hydroxocobalamin, the patient demonstrated partial clinical improvement. He has a sibling with overt hematological abnormalities and subtle neurological abnormalities who is homozygous to the same mutation. Both parents are heterozygous for the same mutation. CONCLUSIONS: In infants presenting with unexplained non-specific neurological symptoms, irrespective of classical signs of vitamin B12 deficiency, evaluation for TCN2 defect should be considered. Early diagnosis and appropriate management can lead to favorable outcomes.

Endo-lysosomal protein concentrations in CSF from patients with frontotemporal dementia caused by CHMP2B mutation.

Introduction: Increasing evidence implicates proteostatic dysfunction as an early event in the development of frontotemporal dementia (FTD). This study aimed to explore potential cerebrospinal fluid (CSF) biomarkers associated with the proteolytic systems in genetic FTD caused by CHMP2B mutation. Methods: Combining solid-phase extraction and parallel reaction monitoring mass spectrometry, a panel of 47 peptides derived from 20 proteins was analyzed in CSF from 31 members of the Danish CHMP2B-FTD family. Results: Compared with family controls, mutation carriers had significantly higher levels of complement C9, lysozyme and transcobalamin II, and lower levels of ubiquitin, cathepsin B, and amyloid precursor protein. Discussion: Lower CSF ubiquitin concentrations in CHMP2B mutation carriers indicate that ubiquitin levels relate to the specific disease pathology, rather than all-cause neurodegeneration. Increased lysozyme and complement proteins may indicate innate immune activation. Altered levels of amyloid precursor protein and cathepsins have previously been associated with impaired lysosomal proteolysis in FTD. Highlights: CSF markers of proteostasis were explored in CHMP2B-mediated frontotemporal dementia (FTD).31 members of the Danish CHMP2B-FTD family were included.We used solid-phase extraction and parallel reaction monitoring mass spectrometry.Six protein levels were significantly altered in CHMP2B-FTD compared with controls.Lower CSF ubiquitin levels in patients suggest association with disease mechanisms.

Case report: Novel compound-heterozygous mutations in the TCN2 gene identified in a chinese girl with transcobalamin deficiency.

Transcobalamin (TC) deficiency is a rare autosomal recessive disease characterized by megaloblastic anemia. It is caused by cellular vitamin B12 depletion, which subsequently results in elevated levels of homocysteine and methylmalonic acid. This disease is usually diagnosed by genetic analysis of the TCN2 gene. Here, we described a 2.2-month-old Chinese girl with TC deficiency presenting with diarrhea, fever and poor feeding. Whole-exome sequencing detected a pair of compound-heterozygous mutations in TCN2 gene, c.754-12C>G and c.1031_1032delGA (p.R344Tfs*20). To our knowledge, it is the first time that they were identified and reported in TC deficiency. This study contributes to a better understanding of the TC deficiency, expanding the spectrum of TCN2 mutations in this disorder and also supporting the early diagnosis and proper treatment of similar cases in the future.

Different Presentations of Patients with Transcobalamin II Deficiency: A Single-Center Experience from Turkey

Objective: Transcobalamin II deficiency is a rare autosomal recessive disease characterized by decreased cobalamin availability, which in turn causes accumulation of homocysteine and methylmalonic acid. The presenting clinical features are failure to thrive, diarrhea, megaloblastic anemia, pancytopenia, neurologic abnormalities, and also recurrent infections due to immune abnormalities in early infancy. Materials and Methods: Here, we report the clinical and laboratory features of six children with transcobalamin II deficiency who were all molecularly confirmed. Results: The patients were admitted between 1 and 7 months of age with anemia or pancytopenia. Unexpectedly, one patient had a serum vitamin B12 level lower than the normal range and another one had nonsignificantly elevated serum homocysteine levels. Four patients had lymphopenia, four had neutropenia and three also had hypogammaglobulinemia. Suggesting the consideration of transcobalamin II deficiency in the differential diagnosis of immune deficiency. Hemophagocytic lymphohistiocytosis was also detected in one patient. Furthermore, two patients had vacuolization in the myeloid lineage in bone marrow aspiration, which may be an additional finding of transcobalamin II deficiency. The hematological abnormalities in all patients resolved after parenteral cobalamin treatment. In follow-up, two patients showed neurological impairments such as impaired speech and walking. Among our six patients who were all molecularly confirmed, two had the mutation that was reported in transcobalamin II-deficient patients of Turkish ancestry. Also, a novel TCN2 gene mutation was detected in one of the remaining patients. Conclusion: Transcobalamin II deficiency should be considered in the differential diagnosis of infants with immunological abnormalities as well as cytopenia and neurological dysfunction. Early recognition of this rare condition and initiation of adequate treatment is critical for control of the disease and better prognosis.

Association of TCN2 rs1801198 c.776G>C polymorphism with markers of one-carbon metabolism and related diseases: a systematic review and meta-analysis of genetic association studies.

Background: Vitamin B-12 (cobalamin) deficiency may produce severe neurologic and hematologic manifestations. Approximately 20-25% of circulating cobalamin binds to transcobalamin 2 (TCN2), which is referred to as active vitamin B-12. The G allele of the TCN2 c.776G>C (rs1801198) polymorphism has been associated with a lower plasma concentration of holotranscobalamin. However, genotype association studies on rs1801198 have led to conflicting results regarding its influence on one-carbon metabolism (OCM) markers or its association with pathologic conditions.Objective: We assessed the association of rs1801198 genotypes with OCM marker concentrations and primary risks of congenital abnormalities, cancer, and Alzheimer disease.Design: We conducted a systematic review of the literature that was published from January 1966 to February 2017 and included all studies that assessed the association between rs1801198 and OCM markers or a pathologic condition.Results: Thirty-four studies met the inclusion criteria. Subjects with the rs1801198 GG genotype had significantly lower concentrations of holotranscobalamin [standardized mean difference (SMD): -0.445 (95% CI: -0.673, -0.217; P < 0.001); I2 = 48.16% (95% CI: 0.00%, 78.10%; P = 0.07)] and higher concentrations of homocysteine (European descent only) [SMD: 0.070 (95% CI: 0.020, 0.120; P = 0.01); I2 = 0.00% (95% CI: 0.00%, 49.59%; P = 0.73)] than did subjects with the rs1801198 CC genotype. The meta-analysis on the association between rs1801198 and methylmalonic acid (MMA) lacked statistical power. No significant difference was observed regarding cobalamin, folate, and red blood cell folate. No significant association was observed between rs1801198 and primary risks of congenital abnormalities, cancer, or Alzheimer disease.Conclusions: Meta-analysis results indicate an influence of rs1801198 on holotranscobalamin and homocysteine concentrations in European-descent subjects. In addition, well-designed and -powered studies should be conducted for assessing the association between rs1801198 and MMA and clinical manifestations that are linked to a decreased availability of cobalamin. This review was registered at www.crd.york.ac.uk/prospero as CRD42017058504.

Autoimmune mechanisms in pernicious anaemia & thyroid disease.

Pernicious anaemia (PA) and some types of thyroid disease result from autoimmune processes. The autoimmune mechanisms in these conditions have not been fully elucidated. This review discusses the autoimmune mechanisms involved in PA and how these affect diagnosis and disease progression. In addition to gastric antibodies, antibodies to the vitamin B12 binding protein transcobalamin which can result in high serum B12 levels are also addressed with regard to how they affect clinical practice. The role of autoimmune susceptibility is investigated by comparing PA to one of its most common comorbidities, autoimmune thyroid disease (AITD). Thyroid disease (although not exclusively AITD) and B12 deficiency are both also implicated in the pathology of hyperhomocysteinemia, an elevated homocysteine in plasma. Since hyperhomocysteinemia is a risk factor for cardiovascular occlusive disease, this review also addresses how thyroid disease in particular leads to changes in homocysteine levels.

Transcobalamin II (TCN2 67A>G and TCN2 776C>G) and transcobalamin II receptor (TCblR 1104C>T) polymorphisms in Korean patients with idiopathic recurrent spontaneous abortion.

PROBLEM: The transcobalamin II (TCN2) 776C>G polymorphism has been reported to be a genetic risk factor for idiopathic recurrent spontaneous abortion (RSA). However, the sample size in previous studies was small, and other TCN2 polymorphisms have not been studied. Moreover, the TCN2 67A>G and 776C>G polymorphisms, and the transcobalamin II receptor (TCblR/CD320) 1104C>T polymorphism, have demonstrated associations with immune responses. METHOD OF STUDY: Three hundred and seventy-eight RSA patients who had at least two consecutive spontaneous abortions were enrolled. Two hundred and seven control subjects were collected from a convenience sample. Polymerase chain reaction and restriction fragment length polymorphism analysis were performed to identify the TCN2 67A>G and 776C>G polymorphisms, and the TCblR 1104C>T polymorphism. RESULTS: RSA patients showed significantly different frequencies of the TCN2 67AG+GG genotypes compared with control subjects. CONCLUSION: The TCN2 67G allele is a possible risk factor for idiopathic RSA.

Immunohistochemical quantification of the vitamin B12 transport protein (TCII), cell surface receptor (TCII-R) and Ki-67 in human tumor xenografts.

BACKGROUND/AIM: Cancer cells have an essential demand for vitamin B12 (cobalamin) to enable cellular replication. The present pilot study quantified the immunohistochemical expression of vitamin B12 transport protein (Transcobalamin II; TCII), cell surface receptor (Transcobalamin II-R; TCII-R) and proliferation protein (Ki-67) in human tumor xenografts. MATERIALS AND METHODS: Tissue microarray slides containing 34 xenograft tumor tissues were immunohistochemically stained using TCN2 (anti-TCII), CD320 (anti-TCII-R) and MIB-1 (anti-Ki-67) antibodies. Representatively stained areas of all slides were digitally imaged and protein expression was quantified using ImageJ software plugins. RESULTS: All xenograft tumor tissues stained positively for TCII, TCII-R and Ki-67 proteins; expression varied both within and between tumor types. Correlation between TCII/TCII-R and Ki-67 expression was not significant in xenograft tissues. CONCLUSION: Proliferating cancer cells express measurable levels of TCII and TCII-R. Immunohistochemical quantification of these markers may be useful as a tool for detection of tumors, tailored selection of anti-tumor therapies and surveillance for evidence of recurrent disease.