title: The effect of shared genetic and environmental factors on periodontal disease parameters in untreated adult siblings in Guatemala.
abstract: BACKGROUND
  Increasing evidence supports the role of genetic factors in susceptibility to infectious diseases, including chronic periodontitis. The role of genetic factors in phenotypic expression can be estimated from the degree of resemblance between relatives, as compared with that of unrelated members of a population. Heritability is an estimate of the proportion of total phenotypic variation of a quantitative trait, which is attributable to genetic factors, and is based on the variance within versus between family members. The aim of this study was to determine whether there is a familial basis for periodontal disease status in an untreated population in Guatemala using heritability estimates as a measure of familial clustering of disease.
  
  
  METHODS
  One-hundred and thirteen adult subjects (including both siblings and spouse pairs), age range 35 to 60 years, participated in this study. Full-mouth periodontal examinations were performed and heritability estimates were calculated for mean plaque score, mean gingival index (GI), probing depth (PD), and clinical attachment level (CAL). Intraclass correlation coefficients (ICCs) were calculated using the same parameters for spouses to determine whether a common family environment in adulthood plays a role in disease expression.
  
  
  RESULTS
  Only in the case of mean plaque score and mean recession score were heritability estimates significantly above zero at alpha = 0.05. For spouse pairs, mean GI score, mean PD, and percentage of sites of PD > or = 5 mm showed a statistically significant ICC.
  
  
  CONCLUSIONS
  These results lead us to reject the hypothesis that there is substantial heritability for periodontal disease expression in this population. This may be due to an underlying lack of genetic variation within this sample or may indicate that, compared with the role of environmental factors, the genetic contribution to periodontal disease phenotypes is relatively minor.
authors.affiliation: Department of Periodontics, Indiana University School of Dentistry, Indianapolis 46202, USA. sdowsett@iupui.edu
authors.forename: Sherie A
authors.initials: SA
authors.lastname: Dowsett
authors.forename: Luis
authors.initials: L
authors.lastname: Archila
authors.forename: Tatiana
authors.initials: T
authors.lastname: Foroud
authors.forename: Daniel
authors.initials: D
authors.lastname: Koller
authors.forename: George J
authors.initials: GJ
authors.lastname: Eckert
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Kowolik
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001424:Bacterial Infections / Q000208:ethnology / Q000635:transmission; D003774:Dental Plaque Index; D018562:Disease Transmission, Infectious; D005192:Family Health; D005260:Female; D006166:Guatemala / Q000453:epidemiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D017622:Periodontal Attachment Loss / Q000235:genetics; D010512:Periodontal Index; D010518:Periodontitis / Q000208:ethnology* / Q000235:genetics*; D019655:Quantitative Trait, Heritable; D035781:Siblings; D012907:Smoking; D013029:Space-Time Clustering; D018454:Spouses; D018709:Statistics, Nonparametric