Background and aims: We previously reported BMI heritability in the UAE to be 39.9%; indicating a high (60.1%) contribution of environmental factors to obesity. This study aims to determine and compare co-twin monozygotic (MZ) and dizygotic (DZ) BMI concordances.
Materials and methods: 200 twin pairs were identified (ICLDC patient database) and split into two age groups (≤18 and >18 years old). Opposite gender twin sets were considered DZ. In same gender twin sets zygosity was defined according to height differences between co-twins (≥5 cm = DZ). BMI concordance was defined as a difference of <3 kg/m2. Concordance rates were calculated via pairwise concordance formulae then used to calculate the likelihood ratio (X2) i.e. the significance of the difference between MZ and DZ concordance rates (critical value of 3.84 was based on 1 degree of freedom at a 0.05 statistical significance level).
Results: For children and adolescent twin sets (n=96, mean age 10.9 ± 4.1 years, BMI 18.9 ± 6.4 kg/m2), (1) 64 pairs were concordant (MZ: 27 pairs)), (2) 32 pairs were discordant (MZ: 8 pairs)), (3) calculated pairwise concordance was MZ: 0.77 and DZ 0.61 and (4) X2 for BMI concordance between MZ and DZ was 1.22. For the 104 adult twin sets: (mean age 46.8 ± 16.8 years, BMI 28.4 ± 6.7 kg/m2), (1) 53 pairs were concordant (MZ: 28 pairs), (2) 51 pairs were discordant (MZ: 40 pairs), (3) calculated pairwise concordance was MZ: 0.41 and DZ: 0.69 and (4) X2 for BMI concordance between MZ and DZ was 3.34.
Conclusion: Following null hypothesis X2 model analysis, no association between zygosity and BMI concordance was indicated suggesting that environmental factors have a larger impact on BMI than genetics in this population.