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.