Genetic and Secondary Causes of Obesity Among Adults in Saudi Arabia: A Systematic Review

Abstract

Background: Prevalence of obesity in Saudi Arabia is above 35% among the adult population, making it a major burden on public health. Lifestyle factors such as diet and physical activity are clearly involved, however secondary causes of obesity, such as endocrine disorders, drugs and genetic factors are still not well studied in this population. This systematic review was conducted to pool evidence for the rates and patterns of secondary causes of obesity in adults from the Saudi Arabian region.

Methods: Methods We performed a systematic review following the PRISMA 2020 statement. The search was conducted in PubMed and Cochrane databases to identify studies reporting secondary causes of obesity in adults in Saudi Arabia without date or language restrictions. Two reviewers independently screened articles, extracted data and assessed quality using relevant risk of bias tools. The primary results were the frequency of endocrine causes of (hypothyroidism, polycystic ovary syndrome [PCOS], Cushing’s syndrome), drug-induced obesity and genetic aetiologias. Secondary results were the diagnostic criteria adopted, and distribution patterns according to demographic subgroups.

Results: Out of 1,247 records identified, 30 were assessed for full-text review and 7 studies were included (n=1,063 participants). Neither studies on Cushing's syndrome nor on drug-related obesity as secondary causes were identified. Five studies previously investigated genetic factors (n=750), mainly focusing on obesity-related polymorphisms in the FTO, MC4R, BDNF and ACE genes. In PCOS, FTO rs17817449 and rs1421085 were significantly associated with obesity (p<0.05). Strong associations with obesity were also observed for MC4R variants rs12970134 and rs17782313 (OR=1.348 and OR=1.364, p=0.002, respectively). The largest effect was detected for the BDNF variant rs10767664 (OR=1.923, p=0.00072). PCOS was studied in 4 (n=439) studies; these studies examined genetic and metabolic factors rather than prevalence. Only one study discussed hypothyroidism, evaluating remission after bariatric surgery but without records of baseline prevalence. Meta-analysis was not feasible due to major methodological heterogeneity and incomplete reporting. Quality assessment, Type of analysis. Most of the studies showed moderate to high risk of bias, with the majority of bias arising from small sample sizes, non population-based sampling and insufficient control for confounding.

Conclusions: This systematic review exposes a challenge of secondary causes of obesity in SA adults that the current evidence is insufficient to address and further high-quality research is needed. Although markers of genetic susceptibility show interesting associations, in particular for FTO, MC4R and BDNF variants, population-based studies on the prevalence of endocrine disorders and drug-related obesity virtually do not exist. The absence of screening data for hypothyroidism, Cushing’s syndrome, and drug-induced obesity is a major void in clinical knowledge. Recommendations for future research Population-based studies using uniform diagnostic criteria should be given priority in order to serve as basis for screening recommendations and for clinical practice in Saudi Arabia.