Impact of Two Common Polymorphisms in the PPAR Gene on Glucose Tolerance and Plasma Insulin Profiles in Monozygotic and Dizygotic TwinsThrifty Genotype, Thrifty Phenotype, or Both?
-
首席医学网
2004年11月01日 10:09:48 Monday
-
作者:Pernille Poulsen Gitte Andersen Mogens Fenger Torben Hansen Søren M. Echwald Aage Vølund Henning Beck-Nielsen Oluf Pedersen and Allan Vaag
加入收藏夹
【关键词】 Two,Common,
1 Department of Endocrinology, Odense University Hospital, Odense C, Denmark
2 Steno Diabetes Center, Gentofte, Denmark
3 Department of Clinical Biochemistry, Hvidovre Hospital, Hvidovre, Denmark
4 Novo Nordisk, Research and Development, Biostatistics, Bagsværd, Denmark
| ABSTRACT |
|---|
| TOP ABSTRACT RESEARCH DESIGN AND METHODS RESULTS DISCUSSION REFERENCES |
|---|
The Pro12Ala polymorphism in the PPAR2 gene has been associated with reduced risk of type 2 diabetes and insulin resistance. Recently, an association between dizygotic twinning and PPAR gene polymorphisms has been proposed. We investigated the phenotypic appearance of the two polymorphisms (Pro12Ala and exon 6 CT) in PPAR among elderly twins (207 monozygotic [MZ] and 342 dizygotic [DZ]) and evaluated whether they could explain previously reported differences in plasma glucose and insulin profiles among MZ and DZ twins. We demonstrated a significant impact of the Pro12Ala polymorphism on glucose tolerance, diabetic status, homeostasis model assessment for insulin resistance, and plasma insulin profiles in twins. No impact of the silent exon 6 polymorphism on glucose homeostasis or plasma insulin profiles was found. Independent of the polymorphisms, we observed a significant impact of zygosity status per se on the plasma insulin profile after oral glucose ingestion, with the MZ twins being more hyperinsulinemic, indicating insulin resistance, than the DZ twins. Nonsignificantly higher glucose concentrations were observed among MZ compared with DZ twins. We demonstrated an association between the Ala allele and reduced risk of diabetes and insulin resistance in twins. However, the differences in metabolic profiles among MZ and DZ twins were not explained by differences in frequencies of the genetic variants and may be due to intrauterine environmental factors operating in twins independent of genotype. Accordingly, our study simultaneously supports a role for both the intrauterine environment (thrifty phenotype) and for genetics (thrifty genotype) in the etiology of insulin resistance and perhaps glucose intolerance in twins.
The association between birth anthropometry and glucose intolerance and/or type 2 diabetes has consistently been demonstrated in several epidemiological studies among singletons (1). However, it has been proposed that the association may be due to a genotype leading to both low birth weight and subsequent development of diabetes in adult life (2). Among a homogenous population-based twin sample, we have recently reported elevated levels of plasma glucose and insulin after oral glucose ingestion among monozygotic (MZ) compared with dizygotic (DZ) twins (3), supporting a role of the intrauterine environment on glucose homeostasis given the more adverse intrauterine conditions characterizing MZ pregnancies (4). Although other studies have not replicated these findings in younger twin populations (5,6), we have recently demonstrated a lower in vivo insulin action, measured by the euglycemic hyperinsulinemic clamp technique, among elderly MZ compared with DZ twins (7).
A recent study reported a higher frequency of the silent CT substitution in exon 6 of PPAR among DZ relative to MZ twins of different ethnic origins (8). The authors concluded that this silent mutation may be linked to DZ twinning and involved in intrauterine survival of DZ twins. Although the frequency of the Pro12Ala polymorphism was similar among MZ and DZ twins, some evidence of transmission disequilibrium was reported for the combination of the two different polymorphisms from the parents of the DZ twins. Another recent study found no linkage between PPAR and dizygotic twinning. The study, however, did not report allele or genotype frequencies among MZ and DZ twins (9).
Peroxisome proliferator activated receptors (PPARs) are members of the nuclear hormone receptor family of transcription factors and are involved in adipocyte differentiation and gene expression. The common Pro12Ala polymorphism of PPAR2, initially identified by Yen et al. (10), has inconsistently been associated with protection against type 2 diabetes and associated diabetic traits, including insulin resistance (11

