Evidence of complex involvement of serotonergic genes with restrictive and binge purge subtypes of anorexia nervosa.

OBJECTIVES: There is mixed evidence of association of serotoninergic genes with anorexia nervosa (AN), but substantial evidence for the involvement of serotonergic mechanisms in appetite control. This study was designed to investigate possible associations between the two subtypes of AN (Restricting-RAN, and Binge-purging-BPAN) and polymorphisms within five genes encoding for proteins involved in the serotoninergic system. METHODS: In order to carry out this investigation we have conducted a case-control association study on 226 females meeting the criteria for AN, and 678 matched healthy females. RESULTS: Our data show a significant association between polymorphisms with the gene encoding HTR2A with both AN subtypes, an association between polymorphisms within the genes encoding HTR1D and HTR1B with RAN, and an association between polymorphisms within the gene encoding HTR2C with BPAN. No associations were found for any polymorphisms of the serotonin transporter gene. This outcome indicates a substantial and complex inter-relationship between serotoninergic genes and AN. CONCLUSIONS: Given these data we hypothesis that the expression or control of expression of several genes of the serotoninergic system, and interactions between these genes, could exert considerable influence over the specific symptomatology of the subtypes of AN.

Further evidence of association of OPRD1 & HTR1D polymorphisms with susceptibility to anorexia nervosa.

BACKGROUND: A recent study reported strong evidence for the involvement of a region on human chromosome 1 and genetic susceptibility to anorexia nervosa (AN). A more detailed analysis of this region has suggested 2 genes that may account for this susceptibility. These data suggest that polymorphisms in both the serotonin 1D (HTR1D) and opioid delta 1 (OPRD1) receptor genes show a significant association with restricting AN (RAN). METHODS: In the current study, we have conducted an independent association study on 226 females meeting DSM-IV criteria for AN and 678 matched volunteers. RESULTS: We genotyped 4 SNPs in HTR1D and 6 SNPs in OPRD1. 3 SNPs were found to be associated with both RAN and binge-purge AN (BPAN) within the gene for OPRD1. We also found evidence of association between 2 polymorphisms within HTR1D and RAN. CONCLUSIONS: These data support the hypothesis that polymorphisms within this region form a component of the genetic basis to susceptibility to RAN. However, further work is required to understand the processes that may be mediated by these genes.

Pharmacogenetics and obesity: common gene variants influence weight loss response of the norepinephrine/dopamine transporter inhibitor GW320659 in obese subjects.

BACKGROUND: GW320659, a highly selective neuronal norepinephrine and dopamine re-uptake inhibitor, has been evaluated for the treatment of obesity. Scrutiny of the weight loss data from a phase II study (GlaxoSmithKline study OBS20001) showed a wide variation in weight loss response following GW320659 treatment and the possibility that the study population might include subgroups with enhanced weight loss response. METHODS: Pharmacogenetic analysis was performed in 191 subjects prospectively ascertained from a Phase II dose ranging study to evaluate the influence of genotype on weight loss efficacy and safety of GW320659 in obese subjects. RESULTS: Common genetic polymorphisms in the drug target (norepinephrine transporter protein 1, SLC6A2) and mechanism pathway (NMDA receptor channel NR1 subunit, GRIN1) were associated with increased weight loss following GW320659 treatment in a proportion (36%) of the study population. In the patient subgroup selected for these genotypes, GW320659 (15 mg/day) produced a significant difference in mean weight loss of 7.84 kg (SD 5.23, n = 14), compared to 2.53 kg (SD 5.17, n = 24) in the subgroup that did not possess the genotypes (P = 0.006). This subgroup also showed a highly significant weight loss response for GW320659 compared to placebo (+0.31 kg, SD 3.32, n = 16) with the same genotypes (P < 0.0001). In addition, there was no difference in placebo response between either subgroup. CONCLUSIONS: Polymorphisms in SLC6A2 and GRIN1 could be used to maximize effective obesity pharmacotherapy by norepinephrine/dopamine transporter inhibitors by identifying patients that may be predisposed to particularly good treatment weight loss response.

Multiplexed SNP genotyping using the Qbead system: a quantum dot-encoded microsphere-based assay.

We have developed a new method using the Qbead system for high-throughput genotyping of single nucleotide polymorphisms (SNPs). The Qbead system employs fluorescent Qdot semiconductor nanocrystals, also known as quantum dots, to encode microspheres that subsequently can be used as a platform for multiplexed assays. By combining mixtures of quantum dots with distinct emission wavelengths and intensities, unique spectral 'barcodes' are created that enable the high levels of multiplexing required for complex genetic analyses. Here, we applied the Qbead system to SNP genotyping by encoding microspheres conjugated to allele-specific oligonucleotides. After hybridization of oligonucleotides to amplicons produced by multiplexed PCR of genomic DNA, individual microspheres are analyzed by flow cytometry and each SNP is distinguished by its unique spectral barcode. Using 10 model SNPs, we validated the Qbead system as an accurate and reliable technique for multiplexed SNP genotyping. By modifying the types of probes conjugated to microspheres, the Qbead system can easily be adapted to other assay chemistries for SNP genotyping as well as to other applications such as analysis of gene expression and protein-protein interactions. With its capability for high-throughput automation, the Qbead system has the potential to be a robust and cost-effective platform for a number of applications.