Diabetes Care, Vol 17, Issue 6 567-573, Copyright © 1994 by American Diabetes Association
NIDDM in Mexican-American families. Heterogeneity by age of onset
BD Mitchell, CM Kammerer, LJ Reinhart and MP Stern
Department of Medicine, University of Texas Health Science Center, San Antonio 78284-7873.
OBJECTIVE--Heredity has long been known as a risk factor for
non-insulin-dependent diabetes mellitus (NIDDM), but the mode of
inheritance of NIDDM remains unclear. We examined the distribution of
diabetes in 29 Mexican-American families ascertained on a diabetic proband.
RESEARCH DESIGN AND METHODS--Probands represented a random sample of
diabetic Mexican Americans residing in low-income neighborhoods from San
Antonio, TX. A total of 375 family members of these diabetic probands were
examined, and diabetes was diagnosed according to the World Health
Organization plasma glucose criteria. RESULTS--The prevalence of diabetes
decreased from 28.2% in first-degree relatives of the probands to 13.3% in
second-degree relatives to 11.1% in third-degree relatives. When compared
with Mexican Americans with no parental history of diabetes, this
represents an excess of diabetes of 2.0-, 1.3-, and 1.1-fold in first-,
second-, and third-degree relatives, respectively. Five of the 29 probands
(17%) had an age of diabetes onset < 40 years. In the first-degree
relatives of these early-onset probands, diabetes prevalence was 47.0% (16
of 34) compared with only 24.1% (34 of 141) in the first-degree relatives
of the 24 late-onset probands. After adjustment for age, this excess
represented a fivefold increase in the odds of diabetes among relatives of
the early-onset probands compared with relatives of the late-onset probands
(P < 0.001). Moreover, the 16 affected family members of the early-onset
probands had a mean age of diabetes onset of 42.7 years compared with 49.9
years for the 34 affected members of the late-onset probands, although this
difference was not statistically significant (P = 0.13). CONCLUSIONS--NIDDM
may be genetically heterogeneous in this Mexican-American population, with
family members of early-onset diabetes patients being at higher risk for
NIDDM than family members of late-onset diabetes patients.