title: Genetic epidemiology of insulin resistance and visceral adiposity. The IRAS Family Study design and methods.
abstract: OBJECTIVE
  Insulin resistance and visceral adiposity are associated with increased risk of type 2 diabetes. In this report, we describe the methods of the IRAS Family Study, which was designed to identify the genetic and environmental risk factors for insulin resistance and visceral adiposity.
  
  
  METHODS
  Families from two ethnic groups (African American and Hispanic) have been recruited from three clinical sites. Blood samples for DNA as well as other standard measures were collected. A CT scan (visceral adiposity) and a frequently sampled glucose tolerance test (insulin resistance) were performed. Preliminary estimates of heritability for indirect measures related to insulin resistance and visceral adiposity were obtained using a variance components approach in the first 93 families (approximately 1000 individuals).
  
  
  RESULTS
  Estimates of heritability ranged from low (0.08) for fasting insulin and HOMA, to moderate (0.28) for fasting glucose, to high (0.54) for BMI. After adjustment for age, gender and ethnicity, all heritability estimates were significantly greater than zero (p < 0.05).
  
  
  CONCLUSIONS
  These results are consistent with the expectation that intermediate measures of insulin resistance and visceral adiposity are heritable, and that the IRAS Family Study has statistical power to detect these intermediate phenotypes of type 2 diabetes and atherosclerosis.
authors.affiliation: Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA. lhenkin@wfubmc.edu
authors.forename: Leora
authors.initials: L
authors.lastname: Henkin
authors.forename: Richard N
authors.initials: RN
authors.lastname: Bergman
authors.forename: Donald W
authors.initials: DW
authors.lastname: Bowden
authors.forename: Darrell L
authors.initials: DL
authors.lastname: Ellsworth
authors.forename: Steven M
authors.initials: SM
authors.lastname: Haffner
authors.forename: Carl D
authors.initials: CD
authors.lastname: Langefeld
authors.forename: Braxton D
authors.initials: BD
authors.lastname: Mitchell
authors.forename: Jill M
authors.initials: JM
authors.lastname: Norris
authors.forename: Marian
authors.initials: M
authors.lastname: Rewers
authors.forename: Mohammed F
authors.initials: MF
authors.lastname: Saad
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Stamm
authors.forename: Lynne E
authors.initials: LE
authors.lastname: Wagenknecht
authors.forename: Stephen S
authors.initials: SS
authors.lastname: Rich
mesh_terms: D000273:Adipose Tissue; D000328:Adult; D001741:Black or African American; D001161:Arteriosclerosis / Q000453:epidemiology / Q000235:genetics; D001823:Body Composition / Q000235:genetics*; D003924:Diabetes Mellitus, Type 2 / Q000453:epidemiology*; D005260:Female; D006630:Hispanic or Latino; D006801:Humans; D007333:Insulin Resistance / Q000235:genetics*; D008297:Male; D008875:Middle Aged