Influence of K656N Polymorphism of the Leptin Receptor Gene on Obesity-Related Traits in Nondiabetic Afro-Caribbean Individuals

Abstract

Background:

Ethnic variations have been reported in allelic frequencies of the leptin receptor gene (LEPR) with population-specific effects. We aimed to explore the association of LEPR polymorphisms with obesity, metabolic syndrome (MetS), and leptin levels in Afro-Caribbean nondiabetic subjects.

Methods:

Genotypic analysis of three LEPR polymorphisms (K109R, Q223R, and K656N) was performed using TaqMan allelic discrimination assays. Associations were measured with phenotypic variables, including body mass index (BMI), waist circumference (WC), and leptin levels. Linear and logistic regressions were performed to evaluate the effects of single-nucleotide polymorphisms (SNPs).

Results:

Mean age was 46 ± 12 years. Among the 375 participants, 29.3% were obese, 36.3% had abdominal obesity, and 18.1% had MetS. Significant association between BMI (P < 0.002) and WC (P < 0.005) was observed for K656N, whereas the associations were not statistically significant for the other two SNPs. No association was found with leptin levels for the three SNPs. The variant allele frequencies for LEPR 109R, 223R, and 656N were 0.16, 0.46, and 0.20, respectively. In dominant models, the variant allele 656N (GC/CC vs. GG) was associated with prevalence of obesity [odds ratio (OR) 1.82; P = 0.012] and abdominal obesity (OR 2.00; P = 0.007), but not significantly with prevalence of MetS (OR 1.72; P = 0.029). Individuals carrying four variant alleles of the three SNPs had a significantly higher risk of obesity (OR 2.86; P = 0.032) than those carrying none variant allele.

Conclusion:

Our results suggest an influence of K656N polymorphism in the LEPR gene on obesity and abdominal obesity in this Afro-Caribbean population.

Introduction

Obesity is a major public health concern, given its association with several chronic diseases. Individuals who are overweight or obese are at increased risk for developing metabolic syndrome (MetS), a clustering of dyslipidemia, abdominal obesity, and hypertension, conferring an increased risk of cardiovascular disease,¹ and abdominal obesity is a central component for this syndrome.² The pathogenesis of obesity is complex, with interaction between genetic and environmental factors.³

Leptin, a cytokine derived from adipose tissues, regulates body weight⁴ and modulates insulin secretion and action via leptin receptors (LEPR) that are present in pancreatic b cells, adipose tissue, muscle,^5,6 and hypothalamus of human subjects.⁷

The leptin receptor is encoded by the LEPR gene located on human chromosome 1. Several single-nucleotide polymorphisms (SNPs) have been described in the human LEPR gene, including the p.K109R (rs1137100), p.Q223R (rs1137101), and p.K656N (rs1805094) polymorphisms. Associations between these polymorphisms and obesity have been studied with contradictory results.^8

–12 However, a meta-analysis concluded that there is no statistical evidence that any allele (K109R, Q223R, or K656N) is associated with body mass index (BMI) or waist circumference (WC) although certain genotypic effects could be population specific.^11,12 Variabilities in LEPR variant frequencies have been reported¹³ and climate has been suggested as an important selective pressure acting on candidate genes for common metabolic disorders.¹⁴

Studies regarding these associations are scarce in non-Caucasian populations and the role of these polymorphisms is not yet studied in our Afro-Caribbean population exhibiting a high prevalence of obesity (23%). The present study aimed to explore the association of leptin receptor polymorphisms (K109R, Q223R, and K656N) with obesity, MetS, and serum leptin concentrations in nondiabetic subjects.

Methods

In a cross-sectional study conducted in the island of Guadeloupe, we studied 375 nondiabetic subjects from the health center of the island. All participants were Afro-Caribbean. The ethnic origin was defined whether the patient defined him/herself and his/her two first-degree relatives as Afro-Caribbean. The exclusion criteria included pregnant women, patients with diabetes, and those with previous cardiovascular complications (coronary artery disease, stroke). The protocol was approved by the ethics committee (South West—Overseas III, Bordeaux, France). All participants provided their written informed consent.

The individuals were interviewed by physicians using a standard questionnaire. Height and weight were measured with participants standing without shoes and lightly clothed. BMI was calculated as weight divided by height squared (kg/m²). These measurements were made by trained nurses and physicians. Blood pressure was measured according to a standardized protocol with an automatic sphygmomanometer. The retained values were the average of two or more readings. Blood samples were obtained from participants after overnight fasting. Plasma cholesterol and triglyceride concentrations were measured by an enzymatic method (Boehringer-Mannheim). Leptin concentrations were measured with enzyme-linked immunosorbent assay kits BioVendor^® (RD191001100).

Genotyping

Genomic DNA was extracted from peripheral white blood cells by standard methods and stored at −20°C until analysis. Genotyping of the study population was performed using a TaqMan allelic discrimination assay according to the manufacturer's instructions (Applied Biosystems, Foster City, CA). After completion of polymerase chain reaction, the results were analyzed by a fluorescence resonance energy transmission (FRET)-based instrument, ABI PRISM 7900HT (Applied Biosystems). The genotypes were called using sequence detection software (SDS) version 2.0.

Three SNPs in LEPR were genotyped: K109R: rs1137100 (Lys109Arg), Q223R: rs1137101 (Gln223Arg), and K656N: rs1805094 (Lys656Asn).

These polymorphisms were chosen because of different arguments from the literature. Differences in LEPR allele frequencies across ethnic groups have been reported^8,13,15 and studies testing the association of K109R, Q223R, and K656N with obesity-related outcomes have shown contradictory results. In addition, studies analyzing these associations are scarce in non-Caucasian populations, highlighting the need to explore these associations in our Afro-Caribbean population exhibiting high prevalence of obesity.

Clinical factors

Overweight was defined as BMI ≥25 kg/m², obesity as BMI ≥30 kg/m², and abdominal obesity as a WC >102 cm in men or >88 cm in women.

MetS was diagnosed according to the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) in patients having at least three of the following five criteria: systolic blood pressure ≥130 and/or diastolic blood pressure ≥85 mmHg, WC >102 cm in men or >88 cm in women (corresponding to abdominal obesity), hypertriglyceridemia with triglyceride level ≥1.69 mmol/L (150 mg/dL), high-density lipoprotein cholesterol level <1.04 mmol/L (40 mg/dL) in men and <1.29 mmol/L (50 mg/dL) in women, fasting plasma glucose level ≥6.1 mmol/L (110 mg/dL), or diabetes.¹

Statistical analyses

Data are presented as numbers (percentages) for categorical variables and as means ± standard deviations for continuous variables. To test percentage and mean differences between groups, we used the chi-squared test and analysis of covariance with adjustment for age and sex, respectively. The genotype and allele frequencies for the analyzed polymorphisms were determined and Hardy–Weinberg equilibrium was evaluated.

We evaluate the combined effects of SNPs on obesity-related phenotypes and leptin level by summing the number of variant alleles of the three SNPs in each subject. These variant alleles were 109R, 223R, and 656N and were considered at risk for obesity in our population.

Linear regressions with adjustment for age, sex, and BMI were performed to evaluate the variation in log leptin levels. The effects of SNPs were assessed by the values of regression coefficients (beta) corresponding to the nonstandardized regression coefficients.

Risks of overweight, obesity, abdominal obesity, and MetS were assessed for each SNP and according to the number of variant alleles using logistic regression models with adjustment for age and sex. Adjusted odds ratios (ORs) and 95% confidence intervals were estimated.

The IBM SPSS Statistics software version 21.0 was used for data analyses. We used P values <0.016 (0.05/3 because three SNPs were tested) for associations with SNPs and P values <0.05 for associations with presence of 1 to 4 variant alleles to declare an association as significant.

Results

Characteristics of the study population

Three hundred seventy-five nondiabetic Afro-Caribbean individuals were included in the study. Among them, 206 (54.9%) were women. The mean age was 46 ± 12 years. The characteristics and genotype distributions of the study population according to gender are shown in Table 1.

Table 1.

Characteristics of the Study Population

Variables	N	All subjects, N = 375		Men, n = 169		Women, N = 206	P
Sex (F)	375	54.9%	169	—	206	—
Age (years)	375	47.9 ± 12.2	169	47.9 ± 12.3	206	47.8 ± 12.4	0.862
WC (cm)	375	89.4 ± 12.3	169	89.2 ± 10.8	206	89.3 ± 13.1	0.718
BMI (kg/m²)	375	27.3 ± 5.9	169	25.7 ± 4.5	206	28.4 ± 6.1	<0.001
Serum leptin (ng/mL)	362	14.4 ± 16.7	162	4.7 ± 5.1	200	22.2 ± 18.6	<0.001
Overweight (%)	375	61.9%	169	54.4%	206	68.0%	0.007
Obesity (%)	375	29.3%	169	18.9%	206	37.9%	<0.001
Abdominal obesity (%)	375	36.3%	169	11.2%	206	56.8%	<0.001
Metabolic syndrome (%)	375	21.6%	169	13.6%	206	28.2%	0.001
rs1137100 A>G	375		169		206
GG		2.9%		3.0%		29.3%	0.910
AG		25.3%		24.3%		26.2%
AA		71.7%		72.8%		70.9%
rs1137101 G > A	375		169		206
AA		21.9%		21.3%		22.3%	0.709
GA		48.0%		50.3%		46.1%
GG		30.1%		28.4%		31.6%
rs1805094 G > C	375		169		206
CC		3.7%		4.1%		3.4%	0.450
GC		32.3%		29.0%		35.0%
GG		64.0%		66.9%		61.7%

Data are presented as mean ± SD or column percentage (%). Significant P values are in bold.

BMI, body mass index; SD, standard deviation; WC, waist circumference.

Among the participants, 29.3% were obese, 61.9% were overweight, 36.3% had abdominal obesity, and 21.6% had MetS. Women had higher BMI (P < 0.001) and higher frequencies of overweight (68.0% vs. 54.4%, P = 0.007), obesity (37.9% vs. 18.9%, P < 0.001), abdominal obesity (56.8% vs. 11.2%, P < 0.001), and MetS (28.2% vs. 13.6%, P = 0.001) than men.

In the whole study population, leptin levels ranged from 1.40 to 103 ng/mL, mean serum leptin was 14.4 ± 16.7 ng/mL and median (interquartile range 25th; 75th percent) was 7.9 (3.0; 21.0) ng/mL. Mean leptin levels were significantly higher in women than in men (22.2 ± 18.6 vs. 4.7 ± 5.1 ng/mL; P < 0.001), in obese than in nonobese (27.2 ± 22.9 vs. 9.1 ± 9.3 ng/mL; P < 0.001), and in subjects with MetS than without MetS (24.0 ± 21.6 vs. 11.9 ± 14.2 ng/mL; P < 0.001).

Positive correlations were found between leptin levels and BMI (r = 0.59; P = 0.023) and between leptin levels and WC (r = 0.44; P < 0.001), data not shown.

The genotype distributions in the study population for LEPR SNPs were within the Hardy–Weinberg equilibrium (1) for rs1137100 A>G (2.9% GG, 25.3% AG, 71.7% AA; P = 0.540), (2) for rs1137101 G > A (21.9% AA, 48% GA, 30.1% GG; P = 0.420), and (3) for rs1805094 G > C (3.7% CC, 32.3% GC, 64% GC; P = 0.070).

No significant difference in genotype frequencies was noted in the three SNPs by sex.

The variant allele frequencies for LEPR 109R, 223R, and 656N were 0.16, 0.46, and 0.20, respectively.

Table 2 presents distribution of anthropometric parameters and leptin levels according to the three SNP genotypes. The P values are provided for dominant models.

Table 2.

Distribution of Leptin Levels and Metabolic Parameters According to LEPR Genotypes

	rs1137100 A>G, K109R			rs1137101 G>A, Q223R			rs1805094 G>C, K656N
	AA, n = 269	GG/AG, n = 106	P	GG, n = 113	AA/GA, n = 262	P	GG, n = 240	CC/GC, n = 135	P
BMI (kg/m²)	27.5 ± 5.7	26.8 ± 6.3	0.228	28.8 ± 6.8	26.9 ± 5.5	0.069	26.6 ± 5.1	29.6 ± 6.9	0.002
WC (cm)	90.0 ± 12.1	87.9 ± 12.9	0.131	89.4 ± 11.6	89.2 ± 12.2	0.426	88.1 ± 12.2	91.7 ± 12.3	0.005
Leptin (ng/mL)	15.0 ± 17.5	12.7 ± 14.2	0.083	14.4 ± 14.9	14.2 ± 17.4	0.983	12.7 ± 14.0	17.4 ± 20.4	0.121

Significant P values are in bold.

LEPR, leptin receptor gene.

Carriers of the variant allele (GC/CC), 656N of rs1805094, had higher mean BMI (29.6 ± 6.9 vs. 26.6 ± 5.1 kg/m², P = 0.002) and WC (91.7 ± 12.3 vs. 88.1 ± 12.2 cm, P = 0.005) than GG carriers. They also had higher frequencies of obesity (P = 0.007) and abdominal obesity (P = 0.004). No significant difference was found in distribution of anthropometric parameters and leptin levels according to rs1137100 K109R and rs1137101 Q223R genotypes (Table 2).

Multivariate linear regression analysis (with adjustment for age, sex, and BMI) of genetic factors associated with log leptin levels found no association with carrying the variant alleles of the three SNPs. The variant alleles 109R (β = −0.027; P = 0.357), 223R (β = −0.005; P = 0.853), and (β = −0.23; P = 0.444) were not independent predictors of fasting serum log leptin levels among our Afro-Caribbean participants (data not shown).

Table 3 presents the adjusted ORs for risk of overweight, obesity, abdominal obesity, and MetS according to each SNP and to the number of variant alleles.

Table 3.

Logistic Regressions of Overweight, Obesity, Abdominal Obesity, and Metabolic Syndrome for LEPR Polymorphisms

	N	Overweight, OR (95% CI)	P	Obesity, OR (95% CI)	P	Abdominal obesity, OR (95% CI)	P	Metabolic syndrome, OR (95% CI)	P
rs1137100 A>G
AA	269	1		1		1		1
GG/AG	106	0.68 (0.43–1.08)	0.103	0.69 (0.41–1.17)	0.168	0.96 (0.54–1.59)	0.783	0.86 (0.48–1.54)	0.619
rs1137101 G > A
GG	113	1		1		1		1
AA/GA	262	0.79 (0.49–1.26)	0.324	0.90 (0.55–1.48)	0.686	1.11 (0.66–1.88)	0.696	1.14 (0.64–2.01)	0.655
rs1805094 G > C
GG	240	1		1		1		1
CC/GC	135	1.43 (0.92–2.26)	0.113	1.82 (1.14–2.90)	0.012	2.00 (1.20–3.33)	0.007	1.79 (1.06–3.03)	0.029
No. of mutant alleles
0	55	1		1		1		1
1	99	0.90 (0.45–1.80)	0.760	1.11 (0.51–1.40)	0.792	1.26 (0.56–2.82)	0.576	0.97 (0.42–2.26)	0.950
2	120	0.70 (0.36–1.38)	0.302	1.63 (0.79–3.38)	0.190	2.09 (0.96–4.52)	0.062	1.22 (0.55–2.72)	0.622
3	71	0.88 (0.42–1.84)	0.727	0.68 (0.28–1.62)	0.379	0.91 (0.38–2.18)	0.838	0.90 (0.36–2.29)	0.832
4	30	2.04 (0.70–5.92)	0.190	2.86 (1.09–7.48)	0.032	2.72 (0.93–7.97)	0.067	1.18 (0.40–3.49)	0.760

Adjustment for age and sex. Significant P values are in bold.

95% CI, 95% confidence interval; OR, odds ratio.

The regressions were performed after adjustments for age and sex.

In dominant models, the rare allele of rs1805094 656N (GC/CC vs. GG) was associated with prevalence of obesity (OR 1.82; P = 0.012) and abdominal obesity (OR 2.00; P = 0.007), but not significantly with prevalence of MetS (OR 1.72; P = 0.029). No significant association was found with rs1137100 109R and rs1137101 223R variant alleles.

The OR for carrying one, two, three, or four variant alleles of the combined three SNPs is also presented.

Individuals carrying four variant alleles of the three SNPs had a significantly higher risk of obesity (OR 2.86; P = 0.032) than those carrying none variant allele.

Discussion

In this study, we examined the association between three LEPR polymorphisms (K109R, Q223R, and K656N) with leptin circulating concentrations, obesity, and MetS risks in an Afro-Caribbean population. We demonstrated that the genetic variant at the LEPR locus, rs1805094 (K656N), was associated with increased risks of overweight and obesity and with a nearly significant risk of MetS, whereas no significant association was found for K109R and Q223R. In addition, subjects carrying four variant alleles of the three SNPs exhibited an increased risk of obesity. However, the three SNPs were not significantly associated with serum leptin concentrations.

Leptin regulates energy balance and acts on appetite and energy expenditure. A higher leptin level has already been associated with both insulin levels and insulin resistance.¹⁶ It was suggested that this adipocyte-derived hormone is an important factor linking obesity, MetS, and cardiovascular disorders.¹⁷ Higher leptin levels were found in women than men, in obese than nonobese, and in individuals with MetS than without MetS in the present study. Positive correlations were also found between leptin levels and BMI and WC. Similar findings were reported in many studies. The sexual dimorphism in leptin levels might be explained by differences in body composition and sex hormone levels between genders. In fact, in our study population, a significantly higher frequency of obesity was noted in women (37.9%) than in men (18.9%).

Leptin exerts its physiological effect by binding to the leptin receptor. The LEPR gene maps in humans to the 1p31 chromosome. Three SNPs of the LEPR gene (Q223R, K109R, and K656N) have been studied in different populations for potential associations with obesity, revealing contradictory findings.^{8

–11,15,18,19} Among these polymorphisms, the K656N polymorphism has been less frequently studied. The genotype frequencies of all the three SNPs were not significantly different among gender and our study failed to find an association between serum leptin concentrations and these SNPs.

Ethnic variations have been reported in the association between these polymorphisms and human body composition.^8,12,13 Some studies found no evidence for significant effects of the common variants on obesity or obesity-related phenotypes,^9,19 whereas some others reported positive associations.^10,18 However, meta-analyses from studies on the LEPR gene found no association of the three polymorphisms (K109R, Q223R, and K656N) with BMI and WC in unrelated subjects from diverse ethnic backgrounds in the overall study populations.^8,12,13 Nevertheless, genotypic effects that could be population specific were noted.¹²

We found no association between K109R, Q223R, and obesity or MetS in our study population. In a multiethnic Malaysian suburban population, subjects with LEPR K109 allele had significantly higher adiposity indices and those with LEPR 109R allele who had lower plasma leptin levels than their wild-type allele counterparts.²⁰ In middle-aged Caucasian males from the HERITAGE family study, carriers of the 223R allele showed significant higher values than noncarriers for BMI, fat mass, and leptin levels.¹⁸ An association was also reported between Q223R and MetS in an elderly Caucasian community.¹⁰ Obesity is considered a polygenic disease and different pathways might interact to increase the risk of this metabolic disease. Findings in an African descent population in Brazil highlighted the importance of multilocus effects in the genetic component of obesity.²¹

Significant associations were found in our study between the K656N polymorphism and obesity with an increased risk of obesity and abdominal obesity in carriers of the 656N variant allele. The risk of obesity was multiplied by 1.82 and that of abdominal obesity by 2.00 in carriers of this allele compared with noncarriers. Conversely, this 656N allele was associated with nonobesity markers, such as normal BMI, less thickness of skin-folds, and body perimeters in Mexican children and adolescents.²² The individuals carrying the variant allele 656N also exhibited a nonsignificant higher frequency of MetS (28.1%) than noncarriers (17.9%), P < 0.021. We also noted a significant risk of obesity for the individuals carrying four variants, alleles of the three SNPs compared with those carrying none variant allele, suggesting the possibility of an additive effect. However, we cannot confirm or rebut this hypothesis in the present study, given its limited sample size.

Increased levels of leptin have been positively correlated with obesity. However, no significant differences in leptin levels by genotype were observed for the three studied polymorphisms. Nevertheless, we noted a nonsignificantly higher mean leptin level in carrier of the 656N variant allele than in carrier of the ancestral allele, and these individuals also exhibited a significantly higher BMI and WC.

The sample from this multiethnic population included only people of Afro-Caribbean origin and the ethnic origin was determined if the patient defined him/herself and his/her two first-degree relatives as Afro-Caribbean.

We assumed that the combination of these inclusion criteria could allow the selection of a homogeneous and representative sample of the Afro-Caribbean population. In our study, the minor allele frequencies of the three SNPs were very close to that of the Afro-Caribbean (from Barbados) published in 1000 genome: 0.20 versus 0.21, 0.46 versus 0.44, and 0.16 versus 0.19 for K656N, Q223R, and K109R, respectively. These data suggest that this objective has been achieved.

Ethnic and geographic variations have been reported in allelic frequencies and genotype distributions of the LEPR gene polymorphisms. In a multiethnic study, the proportion of subjects with the homozygous genotype (AA) of Q223R was lower in Caucasians (14%) than in African Caribbean (35%) and African American (33%).¹⁵ In Africa, Nigerian subjects had a higher frequency of the AA homozygous genotype of Q223R (21%) than subjects from Mali (12%).¹⁵ The variant allele frequencies for 223R were 32%–50% in Caucasian populations^23,24 and were very high in Asian populations (85%).^25,26

Several arguments could be advanced to explain the inconsistent results in the associations between LEPR polymorphisms and obesity in previous studies. (1) Some of these studies were conducted in different ethnic groups, sometimes with small sample size. (2) The LEPR gene could be considered a “thrifty” gene.²⁷ The thrifty gene hypothesis²⁸ suggests that genetic susceptibility to obesity may have been favored by the process of natural selection and the “thrifty genotype” would favor fat deposition and survival during famine. However, in modernized societies, this “thrifty genotype” would become disadvantageous, leading to an increased risk of diabetes and obesity. However, this hypothesis is controversial.²⁹ (3) Climate might have a strong influence on human morphology and strong correlations between allele frequencies and climate variables have been reported in relation to common metabolic disorders.^14,30 Hancock et al. analyzed the worldwide spatial distribution of SNP genes involved in metabolic disorders, such as LEPR. ¹⁴ It was suggested that climate has been an important selective pressure acting on candidate genes for common metabolic disorders, and variants that are deleterious in hot equatorial climates could become advantageous (rather than simply neutral) in colder climates.¹⁴ In this line, the 109R allele was reported to increase in frequency with decreasing winter temperatures.³¹ The 109R allele frequency was 16% in our Afro-Caribbean study population, whereas the 109R allele frequencies were found at 24%–27% in European and Caucasian populations.^9,13,19,23 In addition, ultraviolet radiation might influence environmental temperature and might exert a selective pressure on genes involved in diverse biological processes, including energy metabolism.¹⁴

Concerning our Afro-Caribbean individuals, the geographic areas to which their African ancestors belong and the potential climate effects in the Caribbean island could have influenced the LEPR allele frequencies and the associations with obesity and obesity-related traits. This could partly explain why the K656N polymorphism is associated with obesity and abdominal obesity in our study.

Limitations of this study include the cross-sectional design, which limits inferences on causality, the relatively small sample size, and the lack of data on dietary habits. We cannot exclude that the results are false positives, given that similar results were not reported in larger cohorts in other populations.

However, strengths of this present study include (1) that it was conducted on a homogenous sample of nondiabetic Afro-Caribbean subjects, given that population-specific effects of LEPR gene have been previously described and (2) the availability of both genetic data and leptin levels in this population.

Conclusion

Our results suggest an influence of K656N polymorphism in the LEPR gene on obesity and abdominal obesity in this Afro-Caribbean population of Guadeloupe Island. Nevertheless, larger studies, including testing of several genes and data on dietary habits, are needed to better understand the role of the leptin receptor gene in human adiposity.

Footnotes

Acknowledgments

We acknowledge the nurses and physicians of the AGREXAM Health Centre, for their contribution. This study was partly supported by grants from the University Hospital of Guadeloupe.

Authors' Contributions

L.F. was responsible for the study design and performed the data analysis. L.L. performed the genotyping. L.L., V.B.-C., J.-M.L., C.R., and L.F. interpreted the data and drafted the article. All authors revised the article content and approved the final article.

Author Disclosure Statement

There is no scientific overlap or scientific conflict of interest with this study. No competing financial interests exist for the authors.

References

NCEP. Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III) final report. Circulation, 2002; 106:3143–3421.

Lemieux

, Poirier

, Bergeron

, et al. Hypertriglyceridemic waist: A useful screening phenotype in preventive cardiology?. Can J Cardiol, 2007; 23(Suppl B):23B–31B.

Zhao

, Ware

, He

, et al. Interaction between social/psychosocial factors and genetic variants on body mass index: A gene-environment interaction analysis in a longitudinal setting. Int J Environ Res Public Health, 2017; 14:1153.

Meier

, Gressner

. Endocrine regulation of energy metabolism: Review of pathobiochemical and clinical chemical aspects of leptin, ghrelin, adiponectin, and resistin. Clin Chem, 2004; 50:1511–1525.

Kieffer

, Heller

, Habener

. Leptin receptors expressed on pancreatic beta-cells. Biochem Biophys Res Commun, 1996; 224:522–527.

Seufert

, Kieffer

, Leech

, et al. Leptin suppression of insulin secretion and gene expression in human pancreatic islets: Implications for the development of adipogenic diabetes mellitus. J Clin Endocrinol Metab, 1999; 84:670–676.

Considine

, Considine

, Williams

, et al. The hypothalamic leptin receptor in humans: Identification of incidental sequence polymorphisms and absence of the db/db mouse and fa/fa rat mutations. Diabetes, 1996; 45:992–994.

Bender

, Allemann

, Marek

, et al. Association between variants of the leptin receptor gene (LEPR) and overweight: A systematic review and an analysis of the CoLaus study. PLoS One, 2011; 6:e26157.

Echwald

, Sorensen

, et al. Amino acid variants in the human leptin receptor: Lack of association to juvenile onset obesity. Biochem Biophys Res Commun, 1997; 233:248–252.

10.

Gottlieb

, Bodanese

, Leite

, et al. Association between the Gln223Arg polymorphism of the leptin receptor and metabolic syndrome in free-living community elderly. Metab Syndr Relat Disord, 2009; 7:341–348.

11.

Heo

, Leibel

, Boyer

, et al. Pooling analysis of genetic data: The association of leptin receptor (LEPR) polymorphisms with variables related to human adiposity. Genetics, 2001; 159:1163–1178.

12.

Heo

, Leibel

, Fontaine

, et al. A meta-analytic investigation of linkage and association of common leptin receptor (LEPR) polymorphisms with body mass index and waist circumference. Int J Obes Relat Metab Disord, 2002; 26:640–646.

13.

Paracchini

, Pedotti

, Taioli

. Genetics of leptin and obesity: A HuGE review. Am J Epidemiol, 2005; 162:101–114.

14.

Hancock

, Witonsky

, Gordon

, et al. Adaptations to climate in candidate genes for common metabolic disorders. PLoS Genet, 2008; 4:e32.

15.

Ragin

, Dallal

, Okobia

, et al. Leptin levels and leptin receptor polymorphism frequency in healthy populations. Infect Agent Cancer, 2009; 4(Suppl 1):S13.

16.

Esteghamati

, Khalilzadeh

, Anvari

, et al. Association of serum leptin levels with homeostasis model assessment-estimated insulin resistance and metabolic syndrome: The key role of central obesity. Metab Syndr Relat Disord, 2009; 7:447–452.

17.

Patel

, Reams

, Spear

, et al. Leptin: Linking obesity, the metabolic syndrome, and cardiovascular disease. Curr Hypertens Rep, 2008; 10:131–137.

18.

Chagnon

, Wilmore

, Borecki

, et al. Associations between the leptin receptor gene and adiposity in middle-aged Caucasian males from the HERITAGE family study. J Clin Endocrinol Metab, 2000; 85:29–34.

19.

Gotoda

, Manning

, Goldstone

, et al. Leptin receptor gene variation and obesity: Lack of association in a white British male population. Hum Mol Genet, 1997; 6:869–876.

20.

Fan

, Say

. Leptin and leptin receptor gene polymorphisms and their association with plasma leptin levels and obesity in a multi-ethnic Malaysian suburban population. J Physiol Anthropol, 2014; 33:15.

21.

Angeli

, Kimura

, Auricchio

, et al. Multilocus analyses of seven candidate genes suggest interacting pathways for obesity-related traits in Brazilian populations. Obesity (Silver Spring), 2011; 19:1244–1251.

22.

Angel-Chavez

, Tene-Perez

, Castro

. Leptin receptor gene K656N polymorphism is associated with low body fat levels and elevated high-density cholesterol levels in Mexican children and adolescents. Endocr Res, 2012; 37:124–134.

23.

Rosmond

, Chagnon

, Holm

, et al. Hypertension in obesity and the leptin receptor gene locus. J Clin Endocrinol Metab, 2000; 85:3126–3131.

24.

Yiannakouris

, Yannakoulia

, Melistas

, et al. The Q223R polymorphism of the leptin receptor gene is significantly associated with obesity and predicts a small percentage of body weight and body composition variability. J Clin Endocrinol Metab, 2001; 86:4434–4439.

25.

Endo

, Yanagi

, Hirano

, et al. Association of Trp64Arg polymorphism of the beta3-adrenergic receptor gene and no association of Gln223Arg polymorphism of the leptin receptor gene in Japanese schoolchildren with obesity. Int J Obes Relat Metab Disord, 2000; 24:443–449.

26.

Matsuoka

, Ogawa

, Hosoda

, et al. Human leptin receptor gene in obese Japanese subjects: Evidence against either obesity-causing mutations or association of sequence variants with obesity. Diabetologia, 1997; 40:1204–1210.

27.

Kagawa

, Yanagisawa

, Hasegawa

, et al. Single nucleotide polymorphisms of thrifty genes for energy metabolism: Evolutionary origins and prospects for intervention to prevent obesity-related diseases. Biochem Biophys Res Commun, 2002; 295:207–222.

28.

Neel

. The “thrifty genotype” in 1998. Nutr Rev, 1999; 57:S2–S9.

29.

Wang

, Speakman

. Analysis of positive selection at single nucleotide polymorphisms associated with body mass index does not support the “thrifty gene” hypothesis. Cell Metab, 2016; 24:531–541.

30.

Hancock

, Witonsky

, Alkorta-Aranburu

, et al. Adaptations to climate-mediated selective pressures in humans. PLoS Genet, 2011; 7:e1001375.

31.

Loos

, Rankinen

, Chagnon

, et al. Polymorphisms in the leptin and leptin receptor genes in relation to resting metabolic rate and respiratory quotient in the Quebec Family Study. Int J Obes (Lond), 2006; 30:183–190.