Impact Of COMT Haplotypes On Functional Connectivity Density And Its Association With The Gene Expression Of Dopamine Receptors

Objective: Catechol-O-methyltransferase(COMT)affects brain connectivity via modulating dopamine system,with the expected greater effect of haplotypes than single nucleotide polymorphism(SNP).The action pathway from COMT to dopamine to connectivity theoretically depends on the dopamine receptors.Here we aimed to investigate the impact of COMT haplotypes on brain functional connectivity density(FCD)and to disclose the association between the COMT-FCD statistical map and spatial expression of the dopamine receptor genes.Methods: The image and DNA information of 191 Chinese were collected,and they were grouped according to combinations of the three haplotypes.1.Genotyping: For each subject,we extracted genomic DNA from 3000 ?l of whole blood using the EZgene TM Blood g DNAMiniprep Kit(Biomiga Inc,San Diego,CA,USA).The COMT rs6269,rs4633,rs4818 and rs4680 were then genotyped in each subject using the method of PCR and ligation detection reaction.2.Haplotype estimation: Haploview4.2 software [29] was used to calculate the LD relationship between SNPs,and then to define the haplotype blocks.We identified the major haplotypes and their frequencies in our population as well as the individual haplotype assignments using PHASE 2.1.3.Data acquisition and f MRI data preprocessing: MRI data were acquired using a 3.0-Tesla MR system.Then the f MRI data were preprocessed using the SPM8 and DPARSF.Home-written script was utilized to calculate the FCD value of each voxel.4.A one-way analysis of covariance(ANCOVA)was performed to identify brain regions with significant FCD differences among the six haplotype groups and among the genotypic groups of each SNP.Connection probability maps were generated to identify the specific functional connections contributing the significant FCD differences across COMT haplotype groups.We combined AHBA database to investigate the relationship between the FCD difference map and the gene expression of the five dopamine receptors.Results: We found an inverted U-shape modulation of COMT haplotypes on FCD in the left inferior parietal lobule that is mainly connected to fronto-parietal cortices,with APS homozygotes exhibiting greatest FCD.However,we failed to identify any significant effect based on a single SNP.We found the COMT-FCD statistical map was significantly associated with the expression patterns of the DRD1 and DRD2 genes.Conclusion: Our results suggest that COMT haplotypes have greater impact on functional connectivity than a single genetic variation and the association between COMT and connectivity may depend on the gene expression of dopamine receptors.