medwireNews: Genetic variants that increase susceptibility to obesity are associated with increased gains in lean mass, as well as fat mass, during early childhood, meta-analysis findings indicate.

“[O]ur findings suggest that symmetrical rapid growth may identify infants with high lifelong obesity susceptibility”, say Ken Ong (Addenbrooke’s Hospital, Cambridge, UK) and study co-authors.

The team’s analysis included more than 3000 children from four birth cohorts in France, Spain and the UK. The children were assessed at birth and the ages of 1 year, 2–3 years and, for two cohorts, 4–5 years.

An obesity risk-allele score, based on 16 single nucleotide polymorphisms with reported associations with childhood and adult body mass index (BMI), was not associated with length, weight, BMI or body composition at birth.

However, the score was significantly associated with length/height at age 2–3 years and subsequently, with each BMI-increasing allele adding between 0.020 and 0.028 standard deviation score (SDS) to children’s length or height.

“Notably, these genetic obesity variants are unrelated to adult height, indicating that their positive association with childhood height appears to be fully countered by earlier pubertal timing and cessation of growth”, write Ong et al in JAMA Pediatrics.

Weight and BMI also increased more in children with higher obesity risk-allele scores, as did fat and lean mass. Each allele increase in the risk score added between 0.028 and 0.049 SDS to children’s fat mass and between 0.038 and 0.064 SDS to their lean mass, and this remained significant after accounting for length or height, as well as age, gender, maternal height and whether children were exclusively breastfed at 3 months.

But genetic susceptibility to obesity was not significantly associated with children’s percentage fat or their ratio of fat to lean mass.

“Our findings may be surprising considering that these obesity susceptibility loci, individually or in combinations, have been shown to have predominant positive associations with adiposity rather than lean mass”, say the researchers.

However, they note that the specific effects of changes in fat and lean mass during early childhood on later obesity risk are not clearly established.

“A recent meta-analysis showed that formula-fed compared with breastfed infants have greater fat-free mass in early infancy, but then greater fat mass in later infancy, which could indicate that early gains in fat-free mass precede gains in fat mass”, they say.

The team suggests that effects of genetic obesity susceptibility on relative adiposity may emerge as the children get older, possibly around the age of 5–7 years.

By Eleanor McDermid, Senior medwireNews Reporter

JAMA Pediatr 2014; Advance online publication

Free abstract