Abstract
Evidence for a major role of genetic factors in the determination of body mass index (BMI) comes from studies of related individuals. Despite consistent evidence for a heritable component of BMI, estimates of BMI heritability vary widely between studies and the reasons for this remain unclear. While some variation is natural due to differences between populations and settings, study design factors may also explain some of the heterogeneity. We performed a systematic review that identified 88 independent estimates of BMI heritability from twin studies (total 140,525 twins) and 27 estimates from family studies (42,968 family members). BMI heritability estimates from twin studies ranged from 0.47 to 0.90 (5th/50th/95th centiles: 0.58/0.75/0.87) and were generally higher than those from family studies (range: 0.24–0.81; 5th/50th/95th centiles: 0.25/0.46/0.68). Meta-regression of the results from twin studies showed that BMI heritability estimates were 0.07 (P = 0.001) higher in children than in adults; estimates increased with mean age among childhood studies (+0.012/year, P = 0.002), but decreased with mean age in adult studies (−0.002/year, P = 0.002). Heritability estimates derived from AE twin models (which assume no contribution of shared environment) were 0.12 higher than those from ACE models (P < 0.001), whilst lower estimates were associated with self reported versus DNA-based determination of zygosity (−0.04, P = 0.02), and with self reported versus measured BMI (−0.05, P = 0.03). Although the observed differences in heritability according to aspects of study design are relatively small, together, the above factors explained 47% of the heterogeneity in estimates of BMI heritability from twin studies. In summary, while some variation in BMI heritability is expected due to population-level differences, study design factors explained nearly half the heterogeneity reported in twin studies. The genetic contribution to BMI appears to vary with age and may have a greater influence during childhood than adult life.
Highlights
Studies of twins and families have quantified the contribution of genetic variation to inter-individual differences in body mass index (BMI)
In the last comprehensive review of BMI heritability, Maes et al (1997) reported that the proportion of phenotypic variance (V P) that can be attributed to genetic factors (h2) ranged from 0.40 to 0.90 in twin studies and 0.20 to 0.50 in family studies, demonstrating the wide variation in the magnitude of BMI heritability observed both within and between these study designs (Maes et al, 1997)
We aimed to identify papers that have estimated the heritability of BMI, and to identify and quantify by meta-regression the effects of demographic and methodological factors that contribute to the heterogeneity between estimates
Summary
Studies of twins and families have quantified the contribution of genetic variation to inter-individual differences in body mass index (BMI). Genome-wide association studies (GWAS) have so far identified 32 loci robustly associated with adult BMI (Frayling et al, 2007; Loos et al, 2008; Thorleifsson et al, 2009; Willer et al, 2009; Speliotes et al, 2010). Despite highly statistically significant associations, these 32 loci account for less than 2% of the total V P in BMI. Sub-genome-wide significant variants may be able to explain a substantial portion of the unexplained genetic variance of complex traits. Even when considering such variants, the Abbreviations: BMI, body mass index; DZ, dizygotic; MZ, monozygotic
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