title: COL9A3 gene polymorphism and obesity in intervertebral disc degeneration of the lumbar spine: evidence of gene-environment interaction.
abstract: METHODS
  Cross-sectional.
  
  
  OBJECTIVE
  To evaluate the interaction between the COL9A3 gene polymorphism and persistent obesity in relation to lumbar disc degeneration.
  
  
  BACKGROUND
  Obesity has been suggested to be a risk factor for disc degeneration. There is some indication for an association between collagen IX genes and lumbar disc disease characterized by sciatica. However, the interaction between those factors in their influences on the risk of disc degeneration has not been studied.
  
  
  METHODS
  Blood samples from 135 middle-aged men who had undergone magnetic resonance imaging (MRI) of the lumbar spine were analyzed for the presence of an arginine to tryptophan change in the COL9A3 gene (Trp3 allele). The men represented three occupations: 41 were machine drivers, 42 were carpenters, and 52 were office workers. The discs L2/L3-L5/S1 were evaluated on MRI, using decreased signal intensity of the nucleus pulposus, posterior disc bulges, and decreased disc height as signs of disc degeneration. Based on self-reports on body height and weight currently and at the age of 25 years, obesity history was classified as no obesity, persistent obesity, and other. Rothman's synergy index was used as a measure of interaction between two factors.
  
  
  RESULTS
  The Trp3 allele and persistent obesity acted synergistically to increase the risk of dark nucleus pulposus, posterior disc bulge, and decreased disc height at L4/L5; of multilevel posterior disc bulges; and of decreased disc height. From 45% to 71% of disc degeneration among persistently obese individuals with the Trp3 allele could be attributed to the synergism of these two factors.
  
  
  CONCLUSIONS
  The effect of obesity on lumbar disc degeneration seems to be modified by the collagen IX gene polymorphism, so that people who carry the Trp3 allele are at increased risk if they are persistently obese.
authors.affiliation: Department of Epidemiology and Biostatistics, Finnish Institute of Occupational Health, Helsinki, Finland. svetlana.solovieva@occuphealth.fi
authors.forename: Svetlana
authors.initials: S
authors.lastname: Solovieva
authors.forename: Jaana
authors.initials: J
authors.lastname: Lohiniva
authors.forename: Päivi
authors.initials: P
authors.lastname: Leino-Arjas
authors.forename: Raili
authors.initials: R
authors.lastname: Raininko
authors.forename: Katariina
authors.initials: K
authors.lastname: Luoma
authors.forename: Leena
authors.initials: L
authors.lastname: Ala-Kokko
authors.forename: Hilkka
authors.initials: H
authors.lastname: Riihimäki
mesh_terms: D000483:Alleles; D019943:Amino Acid Substitution; D015992:Body Mass Index; D002908:Chronic Disease; D015331:Cohort Studies; D003094:Collagen / Q000235:genetics*; D024081:Collagen Type IX; D015897:Comorbidity; D003430:Cross-Sectional Studies; D004777:Environment; D005387:Finland / Q000453:epidemiology; D005787:Gene Frequency; D006801:Humans; D007405:Intervertebral Disc Displacement / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics*; D008161:Lumbosacral Region; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000175:diagnosis / Q000453:epidemiology*; D009790:Occupations; D016017:Odds Ratio; D011110:Polymorphism, Genetic / Q000235:genetics*; D018570:Risk Assessment; D013131:Spine / Q000473:pathology
chemical_list: C120768:COL9A3 protein, human; D024081:Collagen Type IX; D003094:Collagen