European genetic variants associated with type 2 diabetes in North African Arabs.

AIMS: Recent genome-wide association studies (GWAS) and previous approaches have identified many genetic variants associated with type 2 diabetes (T2D) in populations of European descent, but their contribution in Arab populations from North Africa is unknown. Our study aimed to validate these markers and to assess their combined effects, using large case-control studies of Moroccan and Tunisian individuals. METHODS: Overall, 44 polymorphisms, located at 37 validated European loci, were first analyzed in 1055 normoglycaemic controls and 1193 T2D cases from Morocco. Associations and trends were then assessed in 942 normoglycaemic controls and 1446 T2D cases from Tunisia. Finally, their ability to discriminate cases from controls was evaluated. RESULTS: Carrying a genetic variant in BCL11A, ADAMTS9, IGF2BP2, WFS1, CDKAL1, TP53INP1, CDKN2A/B, TCF7L2, KCNQ1, HNF1A, FTO, MC4R and GCK increased the risk of T2D when assessing the Moroccan and Tunisian samples together. Each additional risk allele increased the susceptibility for developing the disease by 12% (P = 9.0 × 10(-9)). Genotype information for 13 polymorphisms slightly improved the classification of North Africans with and without T2D, as assessed by clinical parameters, with an increase in the area under the receiver operating characteristic curve from 0.64 to 0.67 (P = 0.004). CONCLUSION: In addition to TCF7L2, 12 additional loci were found to be shared between Europeans and North African Arabs. As for Europeans, the reliability of genetic testing based on these markers to determine the risk for T2D is low. More genome-wide studies, including next-generation sequencing, in North African populations are needed to identify the genetic variants responsible for ethnic disparities in T2D susceptibility.

Association of the ENPP1 K121Q polymorphism with type 2 diabetes and obesity in the Moroccan population.

AIM: The ectonucleotide pyrophosphatase/phosphodiesterase 1 enzyme (ENPP1), which downregulates insulin signaling by inhibiting insulin-receptor tyrosine kinase activity, is encoded by the ENPP1 gene. A common functional ENPP1 K121Q polymorphism has been suggested to contribute to insulin resistance, obesity and type 2 diabetes (T2D) in various ethnic groups. For this reason, we assessed the association between the ENPP1 K121Q polymorphism in T2D and obesity phenotypes in the Moroccan population. METHODS: Using LightCycler((R)) technology, we genotyped the ENPP1 K121Q polymorphism in 503 subjects with T2D and 412 normoglycaemic individuals. RESULTS: There was no evidence of an association between ENPP1 K121Q and T2D in either an additive (P=0.99) or recessive mode of inheritance (P=0.47). However, the Q121 variant was significantly more frequent in obese than in non-obese subjects after adjusting for age, gender and T2D status. We observed genetic heterogeneity between obese and non-obese T2D patients (P=0.02). The K121Q polymorphism was associated with T2D in the presence of obesity in both additive (1.55 [95% CI 1.16-2.07]; P=0.003) and recessive (2.31 [95% CI 1.34-3.97]; P=0.002) modes of inheritance. CONCLUSION: Although there was no evidence of an association between the ENPP1 K121Q variant and the general phenotype of T2D, we did find an association with adult obesity and T2D. The Q121 allele frequency in Morocco is 37.3%, placing it between European Caucasians (15%) and Black Africans (79%). This study is the first to report an association between K121Q and metabolic diseases in the Moroccan population.

Genetic study of the CD36 gene in a French diabetic population.

OBJECTIVES: CD36 is a multifunctional membrane receptor widely expressed in different tissues which binds and internalizes oxidized low-density lipoprotein. In rodents, CD36 gene variations modulate glucose homeostasis and contribute to metabolic syndrome associated with type 2 diabetes but the effects in human are unknown. METHODS: We screened the entire coding sequence of the CD36 gene in 272 individuals and we genotyped both rare and frequent variants in 454 T2D subjects and 221 controls. RESULTS: We detected five mutations, P191P and N247S were only found each in one family and did not segregate with diabetes, the three others (A/C-178 in the promoter, A/G-10 in intron 3 and (GGGTTGAGA) insertion in intron 13) being equally frequent in diabetic subjects and in controls. However, adiponectin levels, a marker for insulin sensitivity, were significantly associated with the -178 A/C promoter variant allele (p=0.003, p corrected for multiple testing=0.036), possibly reflecting association with insulin-resistance in the French population. CONCLUSION: Thus, the -178 A/C SNP promoter mutation in the CD36 gene represents a putative genetic marker for insulin-resistance in the French population, although it does not appear to contribute to the genetic risk for T2D.

Genetic variation in the hepatocyte nuclear factor-3beta gene (HNF3B) does not contribute to maturity-onset diabetes of the young in French Caucasians.

Mutations in genes encoding hepatocyte nuclear factor (HNF) are responsible for three of the five subtypes of maturity-onset diabetes of the young (MODY). This observation and molecular studies indicate that the HNF network is required for normal function of pancreatic beta-cells. This suggests that transcription factors involved in this complex network are candidates for genetic defects in MODY. Because the HNF-3beta gene is implicated in this network, we screened it for mutations in 21 probands of French ancestry with clinical diagnosis of MODY and early-onset type 2 diabetes. All of the five known MODY genes, HNF-4alpha, glucokinase, HNF-1alpha, HNF-1beta, and IPF1, were previously excluded as being the cause of diabetes in these families. By direct sequencing, we identified two transitions, an A-to-G at position -213 and a C-to-T at position -63 in the promoter and exon 1, respectively, of the HNF-3beta gene. A G-to-C transversion at position +32 in the intron 1 and three transitions, C-to-T at position 291, A-to-G at position 837, and G-to-A at position 1188 in the exon 3, resulting in noncoding mutations Ala97Ala, Gly279Gly, and Gln396Gln, respectively, were also identified. The allele frequencies were not significantly different between a control group and MODY probands. Familial segregation studies and linkage analysis showed that genetic variation in the HNF-3beta gene is unlikely to be the cause of early-onset type 2 diabetes in these Caucasian families.

Rat gene coding for heart 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase: characterization of an unusual promoter region and identification of four mRNAs.

We have cloned previously a 22-kb rat gene which codes for heart 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase from an ATG located in exon 2. To characterize the promoter of the gene, we have now cloned and sequenced 1.9 kb of its 5' region and show here that it has an unusual structural and functional organization. By S1 nuclease mapping and primer extension we found that this region contains the first, noncoding, exon of a mRNA that we call R3. The sequence upstream from this exon behaved as a promoter in transient transfection assays. These assays also suggested that the gene possesses more than one promoter. Indeed, by reverse transcription-polymerase chain reaction techniques we identified three additional mRNAs that differ by their 5' noncoding exons upstream from the common, coding, exon 2. mRNA R1 contains two 5' noncoding exons located upstream from the first exon of mRNA R3. mRNA R2 contains one 5' noncoding exon located upstream from, and partially overlapping with, the first exon of mRNA R3. mRNA R4 contains one 5' noncoding exon located downstream from the first exon of mRNA R3 but overlapping partially with it. The distribution of these mRNAs in rat tissues was evaluated by reverse transcription--polymerase chain reaction. We conclude that the gene contains four more exons than the 16 previously described and at least three promoters, two of which correspond to exonic sequences. The gene gives rise to at least four mRNAs which are expressed not only in heart but also in most tissues.

Human and rat chromosomal localization of two genes for 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase by analysis of somatic cell hybrids and in situ hybridization.

Two genes encoding 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase were localized in human and rat chromosomes. PFKFB1 (previously PFRX), which encodes the liver and muscle isozymes, was assigned to Xq22-q31 in the rat and to Xq27-q28 in the human by in situ hybridization using probes generated by the polymerase chain reaction. PFKFB2, which encodes the heart isozyme of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase, was assigned to chromosome 13 in the rat and to chromosome 1 in the human by hybridization of DNA from somatic cell hybrids. By in situ hybridization, this gene was localized to the regions 13q24-25 in the rat and 1q31 in the human.

A rat gene encoding heart 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase.

There are at least 3 isozymes of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase, a bifunctional enzyme which catalyzes the synthesis and degradation of fructose 2,6-bisphosphate. A 22-kb rat gene that encodes the heart isozyme has been identified and compared with the 55-kb rat gene encoding the liver and muscle isozymes which had been described earlier. Although these 2 genes include 12 successive similar exons, they contain dissimilar exons at both ends, consistent with the occurrence of different regulatory domains at the N- and C-termini in the 3 isozymes.