The Finnish Health in Teens study — Fin-HIT — is a cohort study including more than 10,000 Finnish adolescents in the age 9-12 years

The Fin-HIT cohort is ideal for studying a series of etiological hypotheses regarding the role of exposures and mediating factors, including genetic susceptibility, epigenetics, and microbiota on the development of body size.

More than 90 genetic loci have been associated with obesity-related traits, however, they only explain a small percentage of the total heritability. DNA methylation (DNAm) is one of several epigenetic mechanisms that cells use to control gene expression, and it varies by genotype, sex, age, cell type and environmental influences, such as smoking. In this study, the Fin-HIT group performed an epigenome-wide association study (EWAS) within the Finnish Health in Teens – Fin-HIT- cohort to identify differential DNAm associated with BMI in adolescents.

DNAm in 3.1 million CpG sites were investigated in saliva samples from 50 lean and 50 heavy 11-year-old Finnish girls. DNAm was most significantly different between the two groups in CpG sites within the NAV3 and MC2R genes. Many of the sites and regions that were differentially methylated were collocated with known obesity-related genes, predominantly in the insulin-melanocotin pathway. The substantial overlap with obesity- and insulin-related genes, including MC2R, IGFBPL1, IP6K1 and IGF2BP1, and the replication of MPL, indicate true associations between the saliva methylome and BMI. Saliva is a readily available source of DNA that can shed light on the etiology of DNAm and obesity. In the future, saliva DNAm can potentially be used as a biomarker to identify persons at risk of developing obesity.

Original study:

Rounge TB, Page CM, Lepistö M, Ellonen P, Andreassen BK, Weiderpass E. Genome-wide DNA methylation in saliva and body size of adolescent girls. Epigenomics 8: 1495-1505, 2016