Genetics explain why some boys and girls are bigger than others

The influence of genetic factors on differences between children's Body Mass Index (BMI) increases from 43% at age 4 to 82% at age 10, reports a new study by researchers at UCL and King's College London. The research, published in the journal Obesity, combined twin and genomic analyses in 2556 pairs of twins from the Twins Early Development Study. Data were collected in England and Wales in 1999 and 2005 when the twins were 4 and 10 years old respectively. The twin analysis confirmed previous studies with a doubling of genetic influence, called 'heritability', showing that the reasons that some boys and girls are bigger than others are 43% genetic at age 4 and 82% genetic at age 10. One explanation for this may be that as children get older, they have increased independence to seek out environmental opportunities to express their genetic predispositions, a process termed 'gene-environment correlation'. Since twin analyses don't involve direct measurement of genes, the researchers used genomic data in the same sample to compare with the twin findings. They first used Genome-wide Complex Trait Analysis (GCTA) which estimates the combined effects of over 1.7 million common genetic variants across the whole genome, to demonstrate that the total effect of common genes increased by 50% between ages 4 and 10.