In our 1 M GWAS, among the top GWAS signals for BMI were 3 variants that mapped within the lysophosphatidylglycerol acyltransferase 1 (LPGAT1) gene. LPGAT1 belongs to a large family of acyltransferases which are involved in a variety of biological processes including pathways that regulate energy homeostasis and body weight. Therefore LPGAT1 was analyzed as a candidate gene for obesity in Pima Indians. Variants (n = 26) located within and adjacent to LPGAT1 including a novel 27 bp deletion identified by sequencing were genotyped in a population-based sample of 3391 full-heritage Pima Indians living in the Gila River Indian Community. Replication of selected variants was assessed in a second sample of 3327 mixed-heritage Native Americans from the same community. Variants with nominal associations with body mass index (BMI) in each of the two independent samples (tagged by rs112662024 and rs12058008) had associations of P = 1-4 x 10-5 in the combined sample (n = 6718). A haplotype that included a novel 27 bp deletion, which does not occur in Caucasians, showed the strongest association with BMI in full heritage Pima Indians. In vitro functional analysis provided suggestive evidence that this 27 bp deletion in the 5-UTR may affect transcriptional or post-transcriptional regulation. Analysis of LPGAT1 cDNA from human preadipocytes identified an additional exon whose sequence could potentially serve as a mitochondrial targeting peptide. In our 1 million SNP GWAS for type 2 diabetes, our strongest finding was with a SNP (rs1861612) in DNER that was associated with type 2 diabetes at genome-wide significance (odds ratio = 1.29 per copy of the T allele, P = 6.6 x 10-8). DNER (delta/notch-like EGF repeat containing) is expressed in islets and mediates notch signaling via cell-cell interaction. Notch signaling is critical for pancreatic development. We assessed the physiologic role of DNER in a mouse -cell line in which DNER was both over-expressed and knocked down by siRNA targeting. Notch pathway specific genes, Notch1, Hes1, and Neurog3 were significantly regulated by DNER (P <0.001), suggesting that alterations in DNER mediate an effect on T2D susceptibility through the notch signaling pathway. Although DNER has not been previously reported in GWASs for type 2 diabetes, NOTCH2 is a highly reproducible type 2 diabetes gene in other ethnicities.
|Hanson, Robert L; Muller, Yunhua L; Kobes, Sayuko et al. (2014) A genome-wide association study in American Indians implicates DNER as a susceptibility locus for type 2 diabetes. Diabetes 63:369-76|
|Muller, Yunhua L; Thearle, Marie S; Piaggi, Paolo et al. (2014) Common genetic variation in and near the melanocortin 4 receptor gene (MC4R) is associated with body mass index in American Indian adults and children. Hum Genet :|
|Traurig, Michael T; Orczewska, Julieanna I; Ortiz, Daniel J et al. (2013) Evidence for a role of LPGAT1 in influencing BMI and percent body fat in Native Americans. Obesity (Silver Spring) 21:193-202|
|Ma, Lijun; Hanson, Robert L; Que, Lorem N et al. (2008) PCLO variants are nominally associated with early-onset type 2 diabetes and insulin resistance in Pima Indians. Diabetes 57:3156-60|