Genetic epidemiology of insulin resistance and visceral adiposity. The IRAS Family Study design and methods.
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.
Henkin
Leora
L
Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA. lhenkin@wfubmc.edu
Bergman
Richard N
RN
Bowden
Donald W
DW
Ellsworth
Darrell L
DL
Haffner
Steven M
SM
Langefeld
Carl D
CD
Mitchell
Braxton D
BD
Norris
Jill M
JM
Rewers
Marian
M
Saad
Mohammed F
MF
Stamm
Elizabeth
E
Wagenknecht
Lynne E
LE
Rich
Stephen S
SS
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