|Maturity onset diabetes of the young (monogenic diabetes)|
|Other names||Monogenic diabetes|
Maturity onset diabetes of the young (MODY) refers to any of several hereditary forms of diabetes mellitus caused by mutations in an autosomal dominant gene disrupting insulin production. MODY is often referred to as monogenic diabetes to distinguish it from the more common types of diabetes (especially type 1 and type 2), which involve more complex combinations of causes involving multiple genes and environmental factors. MODY 2 and MODY 3 are the most common forms. MODY should not be confused with latent autoimmune diabetes of adults (LADA) — a form of type 1 DM, with slower progression to insulin dependence than child-onset type 1 DM, and which occurs later in life.
MODY is the final diagnosis in 1%–2% of people initially diagnosed with diabetes. The prevalence is 70–110 per million people. 50% of first-degree relatives will inherit the same mutation, giving them a greater than 95% lifetime risk of developing MODY themselves. For this reason, correct diagnosis of this condition is important. Typically patients present with a strong family history of diabetes (any type) and the onset of symptoms is in the second to fifth decade.
There are two general types of clinical presentation.
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.
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.
Some sources make a distinction between two forms of monogenetic diabetes: MODY and neonatal diabetes. However, they have much in common and are often studied together.
|MODY 1||hepatocyte nuclear factor 4α||Due to a loss-of-function mutation in the HNF4α gene. 5%–10% cases.|
|MODY 2||glucokinase||Due to any of several mutations in the GCK gene. 30%–70% cases. Mild fasting hyperglycemia throughout life. Small rise on glucose loading. Patients do not tend to get diabetes complications and do not require treatment.|
|MODY 3||hepatocyte nuclear factor 1α||Mutations of the HNF1α gene (a homeobox gene). 30%–70% of cases. Most common type of MODY in populations with European ancestry. Tend to be responsive to sulfonylureas. Low renal threshold for glucose.|
|MODY 4||insulin promoter factor-1||Mutations of the IPF1 homeobox (Pdx1) gene. < 1% cases. Associated with pancreatic agensis in homozygotes and occasionally in heterozygotes.|
|MODY 5||hepatocyte nuclear factor 1β||One of the less common forms of MODY, with some distinctive clinical features, including atrophy of the pancreas and several forms of renal disease. Defect in HNF-1 beta gene. 5%–10% cases.|
|MODY 6||neurogenic differentiation 1||Mutations of the gene for the transcription factor referred to as neurogenic differentiation 1. Very rare: 5 families reported to date.|
|MODY 7||Kruppel-like factor 11||KLF11 has been associated with a form of diabetes that has been characterized as "MODY7" by OMIM.|
|MODY 8||Bile salt dependent lipase||CEL has been associated with a form of diabetes that has been characterized as "MODY8" by OMIM. It is very rare with five families reported to date. It is associated with exocrine pancreatic dysfunction.|
|MODY 9||PAX4||Pax4 is a transcription factor. MODY 9 is a very rare medical condition.|
|MODY 10||INS||Mutations in the insulin gene. Usually associated with neonatal diabetes. Rare < 1% cases.|
|MODY 11||BLK||Mutated B-lymphocyte tyrosin kinase, which is also present in pancreatic islet cells. Very rare.|
|Permanent neonatal diabetes mellitus||KCNJ11 and ABCC8||A newly identified and potentially treatable form of monogenic diabetes is the neonatal diabetes caused by activating mutations of the ABCC8 or KCNJ11 genes which encode subunits of the KATP channel. < 1% cases. Tend to respond to sulfonylureas.|
|Transient neonatal diabetes mellitus||ABCC8||Some forms of neonatal-onset diabetes are not permanent. < 1% cases. Tend to respond to sulfonylureas.|
By definition, the forms of MODY are autosomal dominant, requiring only one abnormal gene to produce the disease; the severity of the disease is moderated by the presence of a second, normal allele which presumably functions normally. However, conditions involving people carrying two abnormal alleles have been identified. Unsurprisingly, combined (homozygous) defects of these genes are much rarer and much more severe in their effects.
Homozygous mutations in the other forms have not yet been described. Those mutations for which a homozygous form has not been described may be extremely rare, may result in clinical problems not yet recognized as connected to the monogenic disorder, or may be lethal for a fetus and not result in a viable child.
The recognised forms of MODY are all due to ineffective insulin production or release by pancreatic beta cells. Several of the defects are mutations of transcription factor genes. One form is due to mutations of the glucokinase gene. For each form of MODY, multiple specific mutations involving different amino acid substitutions have been discovered. In some cases, there are significant differences in the activity of the mutant gene product that contribute to variations in the clinical features of the diabetes (such as degree of insulin deficiency or age of onset).
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 available through commercial laboratories.
In some forms of MODY, standard treatment is appropriate, though exceptions occur:
Chronic hyperglycemia due to any cause can eventually cause blood vessel damage and the microvascular complications of diabetes. The principal treatment goals for people with MODY — keeping the blood sugars as close to normal as possible ("good glycemic control"), while minimizing other vascular risk factors — are the same for all known forms of diabetes.
The tools for management are similar for all forms of diabetes: blood testing, changes in diet, physical exercise, oral hypoglycemic agents, and insulin injections. In many cases these goals can be achieved more easily with MODY than with ordinary types 1 and 2 diabetes. Some people with MODY may require insulin injections to achieve the same glycemic control that another person may attain with careful eating or an oral medication.
When oral hypoglycemic agents are used in MODY, the sulfonylureas remain the oral medication of first resort. When compared to patients with type 2 diabetes, MODY patients are often more sensitive to sulphonylureas, such that a lower dose should be used to initiate treatment to avoid hypoglycaemia. Patients with MODY less often suffer from obesity and insulin resistance than those with ordinary type 2 diabetes (for whom insulin sensitizers like metformin or the thiazolidinediones are often preferred over the sulfonylureas).
According to data from Saxony, Germany, MODY was responsible for 2.4% of diabetes incidence in children younger than 15 years.
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.
Since 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.