Secondary attack rate of type 1 diabetes in Colorado families.
OBJECTIVE
Families of children diagnosed with type 1 diabetes require counseling concerning type 1 diabetes risk in nondiabetic siblings and parents. No U.S. population-specific life-table risk estimates are currently available for parents, and those for siblings (2-6% by age 20 years) are based on family studies completed before 1987.


METHODS
We analyzed family histories of 1,586 patients in Colorado with type 1 diabetes (83% non-Hispanic white, 10% Hispanic, and 7% other) diagnosed before 16 years of age and interviewed during 1999-2002. Families of probands with type 2, undetermined, or secondary diabetes (n = 53) or those with incomplete data (n = 137) were excluded. The median age at onset of the proband was 7.1 years and the median diabetes duration 3.5 years. Cumulative risk estimates were calculated using survival analysis for 2,081 full siblings and 3,016 biological parents.


RESULTS
In siblings, the overall risk of type 1 diabetes by age 20 years was 4.4%, but it was significantly (P < 0.0001) higher in siblings of probands diagnosed under age 7 years than in those diagnosed later. In parents, the overall risk by age 40 years was 2.6% and higher in fathers (3.6%) than in mothers (1.7%) of probands (P < 0.001). Similar to siblings, the risk was also higher (P = 0.006) in parents of probands diagnosed <7 years of age than in those diagnosed later.


CONCLUSIONS
Current risks of type 1 diabetes in Colorado siblings and parents of type 1 diabetic probands are higher than in the 1982 Pittsburgh study but similar to contemporary European rates. Recurrence risk of type 1 diabetes is significantly higher in first-degree relatives of probands diagnosed at a young age.
Steck
Andrea K
AK
Barbara Davis Center for Childhood Diabetes University of Colorado Health Sciences Center, 4200 East 9th Ave., Box B-140, Denver, CO 80262, USA. andrea.steck@uchsc.edu
Barriga
Katherine J
KJ
Emery
Lisa M
LM
Fiallo-Scharer
Rosanna V
RV
Gottlieb
Peter A
PA
Rewers
Marian J
MJ
D000328:Adult; D017668:Age of Onset; D001323:Autoantibodies / Q000097:blood; D002648:Child; D002675:Child, Preschool; D003120:Colorado / Q000453:epidemiology; D003922:Diabetes Mellitus, Type 1 / Q000453:epidemiology* / Q000235:genetics / Q000276:immunology; D005220:Fathers; D005260:Female; D006801:Humans; D015994:Incidence; D007515:Islets of Langerhans / Q000276:immunology; D008297:Male; D009035:Mothers; D015999:Multivariate Analysis; D012307:Risk Factors; D035781:Siblings
D001323:Autoantibodies