Endocrine Abstracts

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.