Structural Analysis Of Candidate Genes For NIDDM/Obesity

如果一个基因在与2型糖尿病/肥胖相关的途径中具有已知的生理功能，或者在另一个人群或动物模型中与糖尿病/肥胖相关，则该基因被认为是皮马印第安人2型糖尿病的候选基因。过去一年分析的候选基因包括：PPARg2、PGC-1、IRS-1、IRS-2、FOXC2和MCR4。在所有这些基因中鉴定出多态性并分析其相关性。例如，黑素皮质素4受体（MC4R）已被确定为人类和啮齿动物中罕见的单基因肥胖的原因。MCR4的杂合编码突变与1%至6%的早期发病或严重成人肥胖有关。作为研究皮马印第安人肥胖易感基因的一部分，我们筛选了MCR4作为候选基因。对96名严重肥胖Pima受试者的MCR4测序发现了两个罕见的编码区变体和一个常见的启动子变体。一个编码变体预测在密码子165 （R165Q）发生精氨酸到赖氨酸的替换，而第二个编码变体是单碱基插入(a)，预测在密码子37处过早停止（TGA）。R165Q先前在其他人群中被发现，功能研究表明它可以显著降低MCR4的活性。相比之下，在核苷酸100上的单碱基插入尚未报道。对一大群皮马印第安人的共同启动子变异基因分型表明，这种变异与一般皮马人的肥胖高度相关。我们目前正在对这个基因进行功能研究。

A gene is considered a candidate gene for type 2 diabetes in Pima Indians if 1) it has a known physiological function in a pathway relevant to type 2 diabetes/obesity or 2) it is associated with diabetes/obesity in another human population or in an animal model. Candidate genes analyzed in the past year include: PPARg2, PGC-1, IRS-1, IRS-2, FOXC2, and MCR4. Poymorphisms were identified in all of these genes and analyzed for association. As an example, the melanocortin 4 receptor (MC4R), has been identified as the cause of rare forms of monogenic obesity in both humans and rodents. Heterozygous coding mutations in MCR4 are implicated in 1 to 6% of early onset or severe adult obesity. As part of our efforts to identify obesity susceptibility loci in the Pima Indians, we screened MCR4 as a candidate gene. Sequencing of MCR4 in 96 severely obese Pima subjects identified two rare coding region variants and one common promoter variant. One coding variant predicts an arginine to lysine substitution at codon 165 (R165Q), while the second coding variant is a single base insertion (A) which predicts a premature STOP (TGA) at codon 37. The R165Q has been previously identified in other populations, and functional studies have shown that it dramatically reduces the activity of MCR4. In contrast, the single base insertion at nucleotide 100 has not yet been reported. Genotyping of the common promoter variant in a large cohort of Pima Indians indicates that this variant is highly associated with obesity in the general Pima population. We are currently pursuing functional studies on this gene.