The influential role of genes in obesity.

: Obesity risk is amplified in the presence of obese relatives yet does not usually follow classic Mendelian inheritance patterns. A combination of gene mutations, deletions and single nucleotide polymorphisms are all known to contribute to obesity. Most cases are polygenic, the result of multiple genes interacting with a changing environment. Each "obesity gene" only makes a small contribution to phenotype, but collectively, inherited genetic variations play a major role in determining body mass and how the body responds to physical activity and nutrition. While obesity is most commonly associated with polygenic inheritance, there are other instances in which the cause is monogenic or syndromic. Monogenic obesity typically is caused by a single gene mutation with severe obesity as the main symptom. Syndromic obesity, on the other hand, has many characteristics, of which obesity is one symptom.