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Maturity onset diabetes of the young (MODY)[1] refers to any of several hereditary forms of diabetes caused by mutations in an autosomal dominant gene (sex independent, i.e. inherited from any of the parents) disrupting insulin production. Unlike the polygenic recessive types 1 and 2 of diabetes caused by mutations in genes inherited from both parents, MODY is monogenic and easier to manage than polygenic ones. 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. MODY may be confused with type 1 or type 2 diabetes. It is not young-onset type 2 diabetes (in a young person), as might erroneously be inferred from the name.
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 the understanding of the pathophysiology of diabetes has improved, 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.
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 accident, when a high glucose is discovered during testing for other reasons, or 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, there are two primary advantages of confirming a diagnosis of MODY. Firstly, 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. Secondly, it may prompt screening of relatives and so help identify 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 KATP channel forms of neonatal-onset diabetes.
The following characteristics suggest the possibility of a diagnosis of MODY in hyperglycemic and diabetic patients:
The diagnosis of MODY is confirmed by specific gene testing, now available through several commercial laboratories.
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