MODY syndrome

Maturity onset diabetes of the young (MODY) refers to any of several rare hereditary forms of diabetes mellitus due to dominantly inherited defects of insulin secretion. As of 2004, six types have been enumerated, but more are likely to be added. MODY 2 and MODY 3 are the most common forms. The severity of the different types varies considerably, but most commonly MODY acts like a very mild version of type 1 diabetes, with continued partial insulin production and normal insulin sensitivity. It is not type 2 diabetes in a young person, as might erroneously be inferred from the name. more...

History of the concept and treatment of MODY

The term MODY dates back to 1964, when diabetes mellitus was considered to have two main forms: juvenile-onset and maturity-onset, which roughly corresponded to what we now call type 1 and type 2. MODY was originally applied to any child or young adult who had persistent, asymptomatic hyperglycemia without progression to diabetic ketosis or ketoacidosis. In retrospect we can now recognize that this category covered a heterogeneous collection of disorders which included cases of dominantly inherited diabetes (the topic of this article, still called MODY today), as well as cases of what we would now call type 2 diabetes occurring in childhood or adolescence, and a few even rarer types of hyperglycemia (e.g., mitochondrial diabetes or mutant insulin). Many of these patients were treated with sulfonylureas with varying degrees of success.

By the 1990s, as our understanding of the pathophysiology of the various forms of diabetes has increased, the concept and usage of "MODY" have become refined and narrower. It is now used as a synonym for dominantly inherited, monogenic defects of insulin secretion occurring at any age, and no longer includes any forms of type 2 diabetes.

Signs, symptoms and differential diagnosis

There are two general types of clinical presentation. Some forms of MODY produce significant hyperglycemia and the typical signs and symptoms of diabetes: increased thirst and urination (polydipsia and polyuria). In contrast, however, many people with MODY have no signs or symptoms and are diagnosed by either (1) accident, when a high glucose is discovered during testing for other reasons, or (2) screening of relatives of a person discovered to have diabetes. Discovery of mild hyperglycemia during a routine glucose tolerance test for pregnancy is particularly characteristic.

MODY cases may make up as many as 5% of presumed type 1 and type 2 diabetes cases in a large clinic population. While the goals of diabetes management are the same no matter what type, the two primary advantages of confirming a diagnosis of MODY are that (1) insulin may not be necessary and it may be possible to switch a person from insulin injections to oral agents without loss of glycemic control, and (2) it may prompt screening of relatives and discovery of other cases in family members.

As it occurs infrequently, many cases of MODY are initially assumed to be more common forms of diabetes: type 1 if the patient is young and not overweight, type 2 if the patient is overweight, or gestational diabetes if the patient is pregnant. Standard diabetes treatments (insulin for type 1 and gestational diabetes, and oral hypoglycemic agents for type 2 are often initiated before the doctor suspects a more unusual form of diabetes. In some forms of MODY, standard treatment is appropriate, though exceptions occur. For example, in MODY2, oral agents are relatively ineffective and insulin is unnecessary, while in MODY1 and MODY3, insulin may be more effective than drugs to increase insulin sensitivity. Sulfonylureas are effective in the K_ATP channel forms of MODYX.

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