Association of the MTHFR C677T polymorphism and fragile X syndrome in an Iranian population

Background & Objective: Fragile X syndrome is one of the most common causes of inherited mental retardation in males after Down syndrome. To date less attention was to study secondary genetic factor that may play role in fragile X neuropathology. In central nervous system, folic acid derivatives participate in different process such as neural development and function, synthesis of neurotransmitters and DNA methylation. This study aimed to assess the possible association of three common polymorphisms of folate pathway key enzymes, methylentetra hydrofolate reductase, MTHFR (C677T and A1298C), and methionine synthase reductase, MTRR (A66G), polymorphisms with the development of fragile X syndrome. Methods: Genetic polymorphisms were examined in a case-control study of 38 unrelated male patients and 60 age/sex matched unrelated controls using PCR-RFLP method. Allele frequencies and genotypes were calculated by chi-square test. Results: signifi cantly increased frequencies of the 677T allele and the 677CT genotype in patients were observed compared to control (p=0.010; OR=2.459 for T allele frequency; p=0.028; OR=2.608 for CT genotype frequency). The statistical analysis demonstrated the signifi cant correlation between C677T MTHFR polymorphism and fragile X syndrome in Iranian population (p=0.018). However, no signifi cant case-control differences were found for A1298C MTHFR and A66G MTRR polymorphisms. Conclusions: The association between C677T MTHFR polymorphism and fragile X syndrome has been demonstrated for the fi rst time in Iran population. This study may be important in better understanding of molecular pathology of fragile X syndrome. Further studies need to be undertaken to evaluate these preliminary results in other populations. Neurology Asia 2012; 17(4) : 347 – 352 Address correspondence to: Dr Ahmad Aleyasin, National Institute of Genetic Engineering and Biotechnology (NIGEB), Shahrak-ePajoohesh, 15th Km, Tehran -Karaj Highway, Tehran, Iran. Tel: 0098-21-44580208, Fax: 00982144580399, Email addresses: [email protected] INTRODUCTION Fragile X syndrome (FXS) is the most common cause of inherited mental retardation, observed in approximately one in 4,000 males and 8,000 females. The diagnosis of FXS was originally based on the expression of a folate-sensitive fragile site at Xq27.3 (FRAXA) induced in cell culture under conditions of folate deprivation. Folate sensitive sites have been located on the X chromosome where FMR1 is located. The mutation responsible for FXS involves expansion of FMR1 CGG repeat segment. The full mutation (>200 CGG-repeats) has been found to be associated with methylation of the promoter region and consequently inactivation of the gene and pathogenesis of FXS. Although it is clear that methylation status plays a role in phenotype, its effect on clinical severity is somewhat unpredictable, especially in females. Two main approaches are used to diagnose the repeat size and methylation statue; polymerase chain reaction (PCR) and Southern blot analysis. However, cytogenetic analysis of metaphase spreads has demonstrated high degree of variability among individuals. Due to the novel nature of the fragile X mutation, inheritance is less straightforward than in classic Mendelian traits. The penetrance of FXS is about 80% in males and 30% in females and there are some males with a fragile X chromosome appeared to be unaffected. Penetrance varies between sibships, even within the same family. There is great variability in the extent of these physical features, with some retarded males showing few of the physical components such as behavioral disturbances-hyperactivity and autism. There is still no medication for FXS which acts directly on the genetic mechanisms or on the immediate result of the genetic defect. Useful pharmacological treatment consists of central nervous system stimulants, clonidine, folic acid, serotonin reuptake inhibitors, and atypical antipsychotics. Neurology Asia December 2012 348 The variable neuropathology may suggest the mutations that have a secondary etiological or pathogenic roles infl uence fragile X neuropathy. To date no report in our knowledge addresses the secondary genetic factor to explain FXS variable characteristics. This study for the fi rst time has evaluated autosomal genes elucidated by folate metabolism that have basic roles in cellular functions and are associated with neurons development and function, synthesis of neurotransmitter and gene methylation. Folate genes mutations, along with dietary declines, have been signifi cantly associated with numerous disorders from birth defects to heart disease and cancer. Folate defi ciencies induce DNA hypomethylation, hyperhomocysteinemia, excision DNA repair and DNA synthesis. It is necessary for the synthesis of purines, thymidilate and S-adenosylmethionine (SAM). Two critical enzymes in folate metabolism pathway are products of methylenetetrahydrofolate reductase (MTHFR) and methionine synthase reductase genes (MTRR). They work in the synthesis of 5-methyltetrahydrofolate and methionine, respectively. Methyltetrahydrofolate, the predominant circulating form of folate, acts as the methyl donor for remethylation of homocysteine to methionine by the vitamine B12 dependent enzyme methionine synthase. Severe MTHFR deficiency is characterized by neurological abnormalities, problem in nerve myelination, and reported to be a risk factor for neural tube defects and chronic neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease and Autism. Transition of cytosine (C) to thymidine (T) at nucleotide position 677 causes alanine to valine substitution and correlate with increases in MTHFR thermolability and reduces enzyme activity. The enzyme activity decreases about 35% in heterozygous C/T genotype and about 70% in homozygous T/T genotype, when compared to the normal C/C genotype. Second common polymorphism in MTHFR gene, the A1298C leads to glutamate to alanine substitution. This decreases MTHFR activity, mostly in CC genotype with no effect on protein thermolability. Methionine synthase reductase is a related fl avoprotein that keeps the methionine synthesis enzyme in an active state for the remethylation of homocysteine to methionine, which is the precursor of SAM. Homocysteine has neurotoxic effects that may also play a role in the neurologic disturbances that are associated with folate defi ciency. MTRR A66G polymorphism decrease the risk of autism whereas MTHFR C677T has been reported to be a risk factor of autism disease, the disease that have some similar behavior disorders with FXS. The present study aimed to determine the putative correlation between the MTHFR C677T, A1298C and MTRR A66G polymorphisms and FXS in the Iranian population.