Genetic and Environmental Contributions to Child Height in Low- and Middle-Income Countries.

BACKGROUND: Child height is influenced by genetic and environmental factors. However, it is unclear how these factors vary by geographical region and by study design, particularly in low- and middle-income countries (LMIC), where data is scarce. Understanding these variations will aid the identification of factors that may be hindering growth in specific populations. METHODS: We analyzed height data of children under 5 years of age from 17 066 twin pairs and 2 024 672 parent-offspring pairs using the Demographic and Health Surveys conducted in 69 countries. We estimated genetic and environmental contributions to child height using a mixture distribution model for twins to account for unknown zygosity and a parent-offspring regression for singletons. A mixture distribution model assumes that the sample comprises a mixture of monozygotic and dizygotic twins and estimates heritability based on the distribution of phenotypic similarity across twin pairs, without requiring prior classification of zygosity. RESULTS: Twin studies consistently estimated heritability at 0.35 (95% CI, 0.34-0.37) across all regions. The estimated proportion of phenotypic variance attributable to shared environmental factors was 0.63 (95% CI, 0.62-0.63), while the contribution of unique environmental factors was 0.02 (95% CI, 0.02-0.02). Conversely, there was variation in the heritability estimates from parent-offspring studies, ranging from 0.27 (95% CI, 0.26-0.30) in North Africa, West Asia and Europe to 0.47 (95% CI, 0.46-0.48) in Latin America and Caribbean. CONCLUSION: The observed discrepancies between twin and family study estimates underscore the complex interplay between genetic and environmental factors. These variations suggest that environmental factors play a critical role in determining height outcomes during childhood. Further research is needed to explore these environmental factors in greater detail with the aim of developing region-specific interventions to address height disparities, particularly in underprivileged regions.