A Link between Obesity and Addiction
Research Unveils a Neurexin 3 and Waist Circumference Association
Jul 9, 2009
Obesity is characterized by the presence of excess fatty tissue, called adipose, usually accumulating around the waist. People with a larger waist circumference are considered more obese and are often of a higher weight and higher cardiovascular risk. Obesity is a major health concern associated with increased morbidity and mortality from cardiovascular complications such as hypertension, diabetes, and heart disease. The condition is the product of both environment (diet and lifestyle) and genetics.
Search for the Obesity Gene
Despite popular clamor for discoveries of an “obesity gene”, the disorder is most likely a polygenic disorder, meaning that a number of genes contribute to its development and maintenance. The disorder is also estimated to be 30–70 percent heritable, meaning that it runs in families with a roughly 50/50 chance of a person having to struggle with it if his parents were obese. Research has identified a few genes with single nucleotide polymorphisms that are associated with increased waist circumference and increased body mass index (BMI), another measure of obesity; the genes include FTO, which is also associated with diabetes susceptibility and food selection, and MC4R, which is associated with fat and energy metabolism.
Recently, a study looking at eight different research projects that investigated more than 31,000 obese individuals found an association between waist circumference and a variant of neurexin 3 (NRXN3), a protein found in the brain.
Neurexin and Obesity
Heard-Costa et al. published their findings in June 2009 in the Public Library of Science (NRXN3 Is a Novel Locus for Waist Circumference, PLoS Genet 5(6)). The researcher group demonstrated an association between a variant, or single nucleotide polymorphism, of the NRXN3 gene and larger waist circumference, higher BMI, and obesity. The findings of the study indicate that the variant influences overall adiposity, that is, the deposition of fatty tissue throughout the body, not just in the abdominal region. This indicates a more complex and generalized role of the protein in fat storage.
The Addiction Pathway
NRXN3 is known to be present in the central nervous system, associated with alcohol dependence, cocaine addiction, and illegal drug abuse. The area of the brain in which the addiction pathway travels also takes part in the learning and reward responses. The addition of fat deposition to the roles of the protein raises the question of obesity as a byproduct of addiction. To what extent does food addiction or desire contribute to obesity? The study suggests that obesity is a centrally-mediated disorder with physiological components, which means it may be treatable by medical means, much like attempts are being made to overcome cocaine addiction with pharmaceuticals.
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