title: Epidemiology and genetics of hypodontia and microdontia: a study of twin families.
abstract: OBJECTIVE
  To identify genetic and environmental factors contributing to hypodontia and microdontia by using Korean twin family data.
  
  
  METHODS
  A total of 1267 individuals (525 men and 742 women; 180 monozygotic twins [MZ] and 43 dizygotic twins [DZ] from 282 families) underwent an oral examination as part of the Healthy Twin Study in Korea. Dental anomalies classified as hypodontia or microdontia were diagnosed using radiographs and clinical examinations. In order to estimate genetic contributions to dental anomalies, we estimated the pairwise concordance rate (PCR), recurrence risk ratio (RRR), and heritability (h2).
  
  
  RESULTS
  The prevalence of hypodontia and microdontia was 3.55% and 3.00%, respectively. MZ had the highest PCR and RRR (13.0-15.3). The PCR and RRR values for both anomalies were much higher for DZ (5.0-11.9) than for siblings (1.4-2.6), despite the fact that DZ pairs and sibling pairs share 50% genetic identity. Further genetic analysis revealed both an additive genetic effect (0.38 when hypodontia and microdontia were pooled) and a strong "twin effect" (0.52 when hypodontia and microdontia were pooled).
  
  
  CONCLUSIONS
  This twin-based study revealed that the formation of dental anomalies is affected by both genetic and environmental factors, and that the impact of these factors varies according to the specific dental anomaly.
authors.affiliation: a  Graduate Student, Department of Orthodontics, Institute of Oral Health Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, Gangnam-gu, Seoul, Korea.
authors.forename: Kwang Ho
authors.initials: KH
authors.lastname: Jeong
authors.affiliation: b  Graduate Student, Department of Epidemiology, School of Public Health, Seoul National University, and Senior Researcher, Health Policy Research Department, Korea Institute for Health and Social Affairs, Seoul, Korea.
authors.forename: Daeeun
authors.initials: D
authors.lastname: Kim
authors.affiliation: c  Professor, Department of Family Medicine, Samsung Medical Center, and Center for Clinical Research, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Yun-Mi
authors.initials: YM
authors.lastname: Song
authors.affiliation: d  Professor, Department of Epidemiology, School of Public Health, Seoul National University, Seoul, Korea.
authors.forename: Joohon
authors.initials: J
authors.lastname: Sung
authors.affiliation: e  Professor and Chairman, Department of Orthodontics, Institute of Oral Health Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Young Ho
authors.initials: YH
authors.lastname: Kim
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D000848:Anodontia / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000235:genetics*; D015331:Cohort Studies; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011859:Radiography; D056910:Republic of Korea / Q000453:epidemiology; D014427:Twins; D055815:Young Adult
keywords: Genetics; Hypodontia; Korean twins; Microdontia