Association of fat mass and obesity-associated (FTO) gene rs9939609 with obesity-related traits and glucose intolerance in an indigenous population, the Xavante

BACKGROUND AND AIMS

Common variants in fat mass and obesity-associated (FTO) gene have been implicated as a susceptibility locus for obesity and type 2 diabetes in different populations. Here, in an indigenous population-based study, we examined whether FTO rs9939609 has a role in susceptibility to glucose intolerance and obesity.

METHODS

The study population comprised 949 full Xavante indigenous people (465 men) aged 18-99 years. The participants were submitted to clinical examination, anthropometrical measures and basal and 2-h post 75g oral glucose load capillary glucose measurements. FTO rs9939609 was genotyped and logistic regression was carried out to test the additive effect of the risk allele.

RESULTS

The frequency of the minor allele of the FTO rs9939609 (0.06) was lower in Xavante than observed in some populations. A significant association between the variant and overweight was observed (OR = 1.56 (95% CI:1.06-2.29, p = 0.02), using an additive model of inheritance, adjusted by age and gender and considering the family structure. We found no associations with obesity or glucose intolerance.

CONCLUSIONS

The FTO rs9939609 is associated with overweight, but not with obesity or glucose intolerance. The low frequency of the A allele suggests that it is not an important risk determinant for these conditions in Xavante indigenous people.

Cardiovascular risk assessment by coronary artery calcium score in subjects with maturity-onset diabetes of the young caused by glucokinase mutations

AIMS

Maturity-Onset Diabetes of the Young (MODY) caused by glucokinase (GCK) mutations is characterized by lifelong mild non-progressive hyperglycemia, with low frequency of coronary artery disease (CAD) compared to other types of diabetes. The aim of this study is to estimate cardiovascular risk by coronary artery calcification (CAC) score in this group.

MATERIALS AND METHODS

Twenty-nine GCK-MODY cases, 26 normoglycemic controls (recruited among non-affected relatives/spouses of GCK mutation carriers), and 24 unrelated individuals with type 2 diabetes were studied. Patients underwent CAC score evaluation by computed tomography and were classified by Agatston score ≥ or < 10. Framingham Risk scores of CAD in 10 years were calculated.

RESULTS

Median [interquartile range] CAC score in GCK-MODY was 0 [0,0], similar to controls (0 [0,0], P = 0.49), but lower than type 2 diabetes (39 [0, 126], P = 2.6 × 10^-5). A CAC score ≥ 10 was seen in 6.9% of the GCK group, 7.7% of Controls (P = 1.0), and 54.2% of individuals with type 2 diabetes (P = 0.0006). Median Framingham risk score was lower in GCK than type 2 diabetes (3% vs. 13%, P = 4 × 10^-6), but similar to controls (3% vs. 4%, P = 0.66).

CONCLUSIONS

CAC score in GCK-MODY is similar to control individuals from the same family and/or household and is significantly lower than type 2 diabetes. Besides demonstrating low risk of CAD in GCK-MODY, these findings may contribute to understanding the specific effect of hyperglycemia in CAD.

Maturity-onset diabetes of the young (MODY) in Brazil: Establishment of a national registry and appraisal of available genetic and clinical data

AIMS

Maturity-Onset Diabetes of the Young (MODY) comprises a heterogeneous group of monogenic forms of diabetes caused by mutations in at least 14 genes, but mostly by mutations in Glucokinase (GCK) and hepatocyte nuclear factor-1 homeobox A (HNF1A). This study aims to establish a national registry of MODY cases in Brazilian patients, assessing published and unpublished data.

METHODS

311 patients with clinical characteristics of MODY were analyzed, with unpublished data on 298 individuals described in 12 previous publications and 13 newly described cases in this report.

RESULTS

72 individuals had GCK mutations, 9 described in Brazilian individuals for the first time. One previously unpublished novel GCK mutation, Gly178Ala, was found in one family. 31 individuals had HNF1A mutations, 2 described for the first time in Brazilian individuals. Comparisons of GCK probands vs HNF1A: age 16±11 vs 35±20years; age at diagnosis 11±8 vs 21±7years; BMI 19±6 vs 25±6kg/m²; sulfonylurea users 5 vs 83%; insulin users 5 vs 17%; presence of arterial hypertension 0 vs. 33%, all p<0.05. No differences were observed in lipids and C-peptide.

CONCLUSIONS

Most MODY cases in Brazil are due to GCK mutations. In agreement with other studied populations, novel mutations are common. Only 14% of patients with familial diabetes carry a HNF1A mutation. Diagnosis of other rare forms of MODY is still a challenge in Brazilian population, as well as adequate strategies to screen individuals for molecular diagnosis.

Erratum: Body composition study by dual-energy x-ray absorptiometry in familial partial lipodystrophy: finding new tools for an objective evaluation

[This corrects the article DOI: 10.1186/1758-5996-4-40.].

Genome-wide analysis in Brazilian Xavante Indians reveals low degree of admixture

Characterization of population genetic variation and structure can be used as tools for research in human genetics and population isolates are of great interest. The aim of the present study was to characterize the genetic structure of Xavante Indians and compare it with other populations. The Xavante, an indigenous population living in Brazilian Central Plateau, is one of the largest native groups in Brazil. A subset of 53 unrelated subjects was selected from the initial sample of 300 Xavante Indians. Using 86,197 markers, Xavante were compared with all populations of HapMap Phase III and HGDP-CEPH projects and with a Southeast Brazilian population sample to establish its population structure. Principal Components Analysis showed that the Xavante Indians are concentrated in the Amerindian axis near other populations of known Amerindian ancestry such as Karitiana, Pima, Surui and Maya and a low degree of genetic admixture was observed. This is consistent with the historical records of bottlenecks experience and cultural isolation. By calculating pair-wise F_st statistics we characterized the genetic differentiation between Xavante Indians and representative populations of the HapMap and from HGDP-CEPH project. We found that the genetic differentiation between Xavante Indians and populations of Ameridian, Asian, European, and African ancestry increased progressively. Our results indicate that the Xavante is a population that remained genetically isolated over the past decades and can offer advantages for genome-wide mapping studies of inherited disorders.

A new method for body fat evaluation, body adiposity index, is useful in women with familial partial lipodystrophy

BMI is a widely used method to evaluate adiposity. However, it has several limitations, particularly an inability to differentiate lean from fat mass. A new method, body adiposity index (BAI), has been recently proposed as a new measurement capable to determine fat excess better than BMI. The aim of this study was to investigate BAI as a mean to evaluate adiposity in a group of women with familial partial lipodystrophy (FPLD) and compare it with BMI. Thirteen women with FLPD Dunnigan type (FPLD2) and 13 healthy volunteers matched by age and BMI were studied. Body fat content and distribution were analyzed by dual X-ray absorptiometry (DXA). Plasma leptin was also measured. BAI was significantly lower in FPLD2 in comparison to control group (24.6 ± 1.5 vs. 30.4 ± 4.3; P < 0.001) and presented a more significant correlation with total fat (%) (r = 0.71; P < 0.001) and fat Mass (g) (r = 0.80; P < 0.001) than BMI (r = 0.27; P = 0.17 for total fat and r = 0.52; P = 0.006 for fat mass). There was a correlation between leptin and BAI (r = 0.57; P = 0.01), [corrected] but not between leptin and BMI. In conclusion, BAI was able to catch differences in adiposity in a sample of FPLD2 patients. It also correlated better with leptin levels than BMI. Therefore, we provide further evidence that BAI may become a more reliable indicator of fat mass content than the currently available measurements.

A functional ABCA1 gene variant is associated with low HDL-cholesterol levels and shows evidence of positive selection in Native Americans

It has been suggested that the higher susceptibility of Hispanics to metabolic disease is related to their Native American heritage. A frequent cholesterol transporter ABCA1 (ATP-binding cassette transporter A1) gene variant (R230C, rs9282541) apparently exclusive to Native American individuals was associated with low high-density lipoprotein cholesterol (HDL-C) levels, obesity and type 2 diabetes in Mexican Mestizos. We performed a more extensive analysis of this variant in 4405 Native Americans and 863 individuals from other ethnic groups to investigate genetic evidence of positive selection, to assess its functional effect in vitro and to explore associations with HDL-C levels and other metabolic traits. The C230 allele was found in 29 of 36 Native American groups, but not in European, Asian or African individuals. C230 was observed on a single haplotype, and C230-bearing chromosomes showed longer relative haplotype extension compared with other haplotypes in the Americas. Additionally, single-nucleotide polymorphism data from the Human Genome Diversity Panel Native American populations were enriched in significant integrated haplotype score values in the region upstream of the ABCA1 gene. Cells expressing the C230 allele showed a 27% cholesterol efflux reduction (P< 0.001), confirming this variant has a functional effect in vitro. Moreover, the C230 allele was associated with lower HDL-C levels (P = 1.77 x 10(-11)) and with higher body mass index (P = 0.0001) in the combined analysis of Native American populations. This is the first report of a common functional variant exclusive to Native American and descent populations, which is a major determinant of HDL-C levels and may have contributed to the adaptive evolution of Native American populations.

Glucose regulates the expression of Gi-proteins in cultured BC3H-1 myocytes

To examine whether glucose has regulatory effects on the expression of Gi-proteins, BC3H-1 myocytes were incubated for 24 hr in the presence of various concentrations of glucose (0-25 mM) and the amount of Gi-proteins was detected by pertussis toxin ADP-ribosylation and immunoblot analysis. Both detection methods showed a progressive decrease in the amount of Gi proteins in cells treated with increasing concentrations of glucose. A maximal reduction of 40% was observed after a 24 hr exposure to 25 mM glucose. The reduction in Gi-proteins correlated with a decrease in insulin-stimulated glucose transport.

Pertussis toxin catalyzed ADP-ribosylation of a 41 kDa G-protein impairs insulin-stimulated glucose metabolism in BC3H-1 myocytes

In this study, we examined the effects of pertussis toxin (PT) on the ADP-ribosylation of guanine nucleotide binding proteins (G-proteins) and various insulin-stimulated processes in cultured BC3H-1 myocytes. Treatment of intact myocytes with 0.1 microgram/ml PT for 24 hours resulted in the complete ribosylation of a 41 kDa protein. The 41 kDa PT substrate was immunoprecipitated with antibodies directed against a synthetic peptide corresponding to a unique sequence in the alpha subunit of Gi-proteins. PT treatment of intact cells had no effect on insulin receptor binding or internalization. However, PT inhibited insulin-stimulated glucose transport at all insulin-concentrations tested (1-100 ng/ml). Maximally stimulated glucose transport was reduced by 50% +/- 15%. Insulin-stimulated glucose oxidation was also decreased by 31% +/- 8%. The toxin had no significant effect on the basal rates of glucose transport and glucose oxidation. The time course of PT-induced inhibition on glucose transport correlated with the time course of the "in vivo" ADP-ribosylation of the 41 kDa protein. The results suggest that a 41 kDa PT-sensitive G-protein, identical or very similar to Gi, is involved in the regulation of glucose metabolism by insulin in BC3H-1 cells.