Starr County Health Studies' Genetics of Diabetes Study

An initial observation in the 1970s that Starr County, Texas, had the highest diabetes-specific mortality of any of the 254 Texas counties led to the establishment of a field office in Rio Grande City, Texas (the county seat of Starr County) and the initiation of a series of studies to understand the epidemiology and genetics of type 2 diabetes, its complications and related conditions in this predominantly (97%) Mexican American population. The field office opened in February 1981 and has operated continuously since then. During this time, three systematic surveys of the population have been conducted as well as family and longitudinal studies. Culturally sensitive diabetes education programs have been developed and implemented and also a weight loss intervention. In total, more than 23,000 Mexican American individuals have been examined with more than 200,000 aliquots of biological specimens stored. Collectively, these studies are known as the Starr County Health Studies. The present Genetics of Diabetes Study has the goal of identifying loci/alleles that underlie susceptibility to type 2 diabetes in this high risk population using genome wide markers and association testing. The study makes use of two primary resources that have been developed in order to identify 1,000 type 2 diabetes cases and 1,000 disease free controls. In the first instance we have identified a subset of unrelated cases from the total cases that we have identified. Where multiply affected sibships were available, the youngest onset case with detailed phenotyping (including assessment of diabetic retinopathy) was selected. Controls came from a recent survey to establish a representative sample of the Starr County population. Blocks were randomly selected, households on selected blocks enumerated and one individual randomly selected from each household for a detailed examination. The examination included an oral glucose tolerance test. Those included as controls are those with no prior diagnosis of diabetes and a negative oral glucose tolerance test. This collection of cases and controls provides the opportunity to identify susceptibility loci for type 2 diabetes and its complications, specifically diabetic retinopathy and albuminuria. The data set also allows the examination of impaired fasting glucose and impaired glucose tolerance. The samples are split between those born in the United States and those born in Mexico and this gives a natural contrast for examining genotype and environmental interactions. It is anticipated that the understanding that will come will lead to strategies for delaying and preventing the onset of diabetes and its complications.]]>
Cases were chosen as individuals with type 2 diabetes that were identified as Mexican Americans. Classification of diabetes was based on National Diabetes Data Group recommendations from 1978. All such individuals also meet current recommendations. Individuals were drawn from several studies that we have conducted in Starr County, Texas. In many cases sibships were recruited. In the case where more than one sibling was eligible, we selected the youngest onset sibling only in order to construct a sample with as few biological relationships as possible. Controls were chosen because they had no history of diabetes and were negative for diabetes on an oral glucose tolerance test using a 75 gm glucose load.]]>
1981 Field office established in Rio Grande City 1983 First systematic survey of the population completed Examinations in 150 pedigrees completed 1985 Second systematic survey begun including abdominal ultrasound 1985 Longitudinal follow-up of 360 individuals with diabetes begun to study retinopathy 1991 Establishment of diabetes affected sibling pair resource begun 1993 Starr County Health Studies Office became an American Diabetes Association GENNID field site 1994 Culturally sensitive diabetes education program developed and testing begun 1995 Starr County Health Studies Office became a field site for the NHLBI Family Blood Pressure Program GENOA network 1996 Completion of first genome wide linkage scan for type 2 diabetes 2000 Identification of calpain 10 as a diabetes susceptibility locus among Mexican Americans 2007 Completion of genome wide linkage scan for diabetic retinopathy 2007 Completion of genome wide association study using Affymetrix HumanMapping 100K set ]]>