VITAMIN B12 DEFICIENCY: CORRELATION BETWEEN MTHFR POLYMORPHISMS AND CLINICAL AND LABORATORY FINDINGS

Background: Vitamin B12 deficiency is a common condition, particularly among the elderly. The classical manifestations include megaloblastic anemia, due to ineffective erythropoiesis, and neurological complication such as peripheral neuropathy, depression, cognitive disturbances and dementia, due to demyelination of the cervical and thoracic dorsal and lateral columns of the spinal cord. Most common causes are pernicious anemia, gastrectomy, ileal resection, atrophic gastritis, long-term vegetarian or vegan dietary. The interaction between folate and B12 is responsible for the megaloblastic anemia seen in both vitamin deficiency. Folate metabolism plays an essential role in DNA synthesis and methylation processes. Methylfolate trap hypothesis is based on the assumption that 5-methyltetrahydrofolate (5-MTHF) cannot be transformed back to its precursor 5,10-methylenetetrahydrofolate (5,10-MTHF), because the reaction catalyzed by MTHFR is irreversible. In cobalamin deficiency, methionine synthase is inactive, causing accumulation of 5-MTHF. So trapped 5-MTHF flows out of the cells, leading a progressive cellular loss of plyglutamated folates. The C677T and A1298C MTHFR gene polymorphisms are associated with a decreased enzyme activity. So homozygous genotype may protect patients with reduced methionine synthase activity from defective DNA synthesis because folate metabolism tends to be shifted to thymidylate synthesis. Aims: Our aim is to examine cobalamin-deficient patients with reduced MTHFR activity, according to the polymorphisms mentioned, in order to evaluate their predisposition to develop anemia, neurological symptom and atrophic gastritis. Methods:We studied 80 Caucasian patients with a diagnosis of megaloblastic anemia consecutively admitted to our Hematology Division from 2006 to December 2013. All patients were tested for C677T and A1298C SNPS by polymerase chain reaction. By univariate analysis we correlate hemoglobin, MCV, white blood count (WBC), neutrophil count, platelets count, folate and B12 levels, neurological symptoms and presence of atrophic gastritis and positivity of parietal cells antibody (PCA) at diagnosis with the distribution of C677T and A1298C genotypes (Table 1). Statistical analysis was performed using Fisher’s exact test and x2 test. Results: We found a correlation statistically significant between patients carrying MTHFR C677T homozygous genotype and lower hemoglobin value (P= 0.022), higher MCV value (P=0.05), lower WBC (P=0.03) and lower platelet count (P=0.05). Forty of the 80 patients had a diagnosis of atrophic gastritis documented by istological examination; twentyseven patients were positive for PCA. We found a significant association between patients carrying MTHFR C677T homozygous genotype and patients with a diagnosis of atrophic gastritis and the absence of antiparietal cell anytibodies (P=0.03). MTHFR A1298C polymorphism showed no correlation with all the variables previously analyzed. Moreover the analysis of plasma levels of folate and vitamin B12 showed the presence of low folate levels in patients with gastric biopsy negative (p=0.02) and antibody negative (P= 0.04).Summary and Conclusions: On the basis of results it can be assumed that MTHFR C677T polymorphism, which shunt folate towards thymidylate synthesis and away from methionine synthesis, do not protect against macrocytic anemia and it is associated with a lower WBC and a lower platelet count. Moreover we can speculate that impaired MTHFR function could increase susceptibility to atrophic gastritis in cobalamin deficient-patient with PCA negativity.