This study investigated the role of genetic variants of Visfatin rs4730153 as risk factors for MetS. The GG genotype, GG+GA genotype and G allele carrier of rs4730153 were risk factors for MetS in interaction with modifying risk factors of obesity, hypercholesterolemia, smoking and food intake, especially in younger age in our population. Furthermore, our results confirm that MetS is multifactorial and that metabolic risk and food intake can modify genetic and MetS association.
A previous study reported that genetic variants of Visfatin rs4730153 played a role in the cardiometabolic risk in Segovia, Spain, with the GG genotype increases the risk for cardiovascular disease assessed with FRAMINGHAM and systematic coronary risk evaluation (SCORE) [8]. Both of these scores included blood pressure and HDL, metabolic risks that were also assessed in the NCEP-ATP III MetS diagnosis. Similarly, a study in China also reported obesity as a risk factor for MetS associated with the GG genotype [11]. Different genotype risks were reported in Han Chinese obese children, where the GG genotype was found to be a protective genotype against hyper-triglycerides [9]. Differences in the genotype risk between populations may be due to ethnicity, the criteria for subject recruitment or environmental factors.
The physiological mechanisms and how these genetic variants contribute to metabolic abnormalities remain unclear. However, an epidemiology study in Saudi Arabia found subjects with GG and GA genotypes had higher plasma Visfatin than the AA genotype [7], which supports the finding that GG genotype is a risk factor for diseases related to higher plasma Visfatin.
Higher plasma levels of Visfatin are associated with its role as a pro-inflammatory cytokine through the activated nuclear factor (NF) ĸB pathway. The upregulation of Visfatin promotes the release of other pro-inflammatory cytokines and has a role in the positive feedback of chronic inflammation, a component of MetS pathophysiology that can alter lipid metabolism, carbohydrate metabolism and adipocyte plasticity. Furthermore, it can lead to cardiometabolic abnormalities [12,13,14,15,16]. The NF-ĸB pathway induced by the increase in Visfatin increases the production of inducible nitrite oxide synthase (iNOS) which leads to endothelial dysfunction, which is also associated with cardiovascular risk, MetS and hypertension [17, 18].
Age stratification was performed in this study based on the Indonesian Health Ministry for determining age groups of adults, pre-elderly and elderly. Participants aged 22–45 years old (younger) were in the adult group, while subjects aged 46–66 years old (older) were in the pre-elderly and elderly groups. Differences in the metabolic profile related to ageing are influenced by hormones, body fat composition, metabolic rate and other environmental factors. These differences may also influence the genetic phenotype association [19, 20]. Also, Visfatin plasma levels decline with age [21], which may temper the impact of NAMPT genetic variants on metabolic risk of phenotype in older age. The association of the NAMPT genetic variant was more prominent with metabolic risk in the younger group which was also found in a Chinese population as well as in our study [9, 11].
The minor allele frequency (MAF) of rs4730153 (0.28) in this study was higher than other studies conducted in Asia (0.08–0.11) but lower than studies in Europe (0.42) or South America (0.50) [8, 10, 11, 22]. The G allele was reported as wild type, which was the same for all studies. The deviation from HWE in our population may be related to the small sample size. Other studies also reported a deviation of HWE in the NAMPT genetic variant in their populations [10, 23]. We performed PCR-RFLP for genotyping, an established, reliable and affordable method for genotyping, especially when resources are limited [24, 25].
This case-control pilot study of a Javanese, especially those who lived in the Yogyakarta region, although small, the number of participants met minimal quota sampling which was calculated based on the hypothesis for an odds ratio for a case-control study. Two large epidemiology studies reported that the prevalence of MetS in Indonesia varies from 21.66 to 39.0% [26, 27]. The study which reported a comparison of the prevalence of MetS among ethnic groups and regions in Indonesia reported a prevalence of MetS in Yogyakarta of 15.4% and the Javanese of 19.85%, lower than the national prevalence [27]. This difference may influence the age of the study participants, time of surveillance performed and methods for diagnosis of MetS component. The laboratory measurement of the two studies used capillary blood but did not mention if the blood sample was fasting and one study did not measure triglycerides [26, 27]. Capillary blood for the measurement of blood glucose and cholesterol is more affordable for large surveillance but not the gold standard for blood glucose, cholesterol and triglycerides. Our study used plasma from the peripheral blood vein collected after 8–10 h of fasting, which is the gold standard for measurement of the metabolite profile.
To the best of our knowledge, this is the first study of the Javanese population who live in Yogyakarta, Indonesia, that reported genetic variants of the NAMPT gene are associated with MetS. However, MetS is a multifactorial disease, with polygenic interactions other than the NAMPT gene, epigenetic regulation, other lifestyle and environmental factors contribute to the pathophysiology. The case and control groups were carefully age- and sex-matched and dietary intake was recorded to reduce research bias. Some limitations of our study were the small sample size and the lack of measurement of plasma Visfatin and physical activities.