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Diabetic Genetics: A Complex Picture

Diabetic Genetics: A Complex Picture

Have any specific genes been identified for type 1 or type 2 diabetes? If so, how many genes are involved?
—MD

The answer to your question depends on the level of proof one requires to establish that a particular gene is a "diabetes gene." Association studies show that certain genetic polymorphisms are more common in persons who have diabetes than in those who do not.1,2 Linkage studies demonstrate that a particular genetic locus is shared by related persons with diabetes more often than would be expected based on chance. In some instances, researchers have determined the location of a gene but have not been able to identify the gene.

Other trials have found associations or links between certain genes and traits associated with diabetes, such as obesity or kidney disease, or with unusual forms of diabetes, such as those characterized by mitochondrial mutations; however, these genes are not necessarily linked to type 1 or type 2 diabetes.

Type 1 diabetes. Linkage studies have strongly implicated 2 genetic regions in type 1 diabetes: HLA and INS. It is unclear how the genes in these regions influence the development of diabetes; they are neither necessary nor sufficient to cause type 1 diabetes. Many other genes have also been implicated in type 1 diabetes. However, these genes either exert less influence or their influence is not as uniform across families as that of HLA and INS.

Type 2 diabetes. Dozens of genes have been implicated in type 2 diabetes. One of these, CAPN10, may exert a modest influence in many persons with diabetes, but it is neither necessary nor sufficient to cause the disease. Many forms of maturity-onset diabetes of youth (an unusual, highly inheritable form of diabetes) seem to be caused by a single gene.

In most persons, many genes probably contribute in small ways to an overall genetic burden that allows diabetes to develop in a particular environment. It also seems likely that differences exist in the combinations of genes that put persons at risk for type 2 diabetes. The genetics of diabetes is extremely complex. We are just beginning to glimpse some of the genes involved, and we can only start to guess at the big picture.

—John B. Buse, MD, PhD, CDE
   Associate Professor of Medicine
   University of North Carolina at Chapel Hill School of Medicine

References

REFERENCES:
1. Froguel P, Velho G. Genetic determinants of type 2 diabetes. Recent Prog Horm Res. 2001;56:91-105.
2. Redondo MJ, Fain PR, Eisenbarth GS. Genetics of type 1A diabetes. Recent Prog Horm Res. 2001;56:69-89.

 
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