Islets of Hope for persons with maturity onset diabetes of the young (MODY)
Article Source: Wikipedia.com (edited for content by Lahle Wolfe, reprinted with permission)
MODY - Quick 101
What is MODY?
Maturity onset diabetes of the young (MODY) is a type of diabetes affecting young people. It runs in families and often onsets before the age of 25.
What is the main defect in MODY?
The main problem relates to the production of insulin by the pancreas.
How common is it?
About 1-2% of people who have diabetes may have MODY.
How is it inherited?
This condition occurs due to inheriting a defective gene from one’s parents. It is Autosomal Dominant which means that just one of the parrents needs to have the condition in order to pass it on.
What are the chances of inheriting it?
If one of the parents has MODY the children will have a 50% chance of inheriting the gene and therfore developing MODY. In other words each child has a 50-50 chance of developing the condition. It is important to recognise that this is a ‘statistical’ estimate of risk. You could have six children and all of them could still be affected and it is equally possible that none are affected.
What are the different types of MODY?
There are 5 genes which have been identified as causing MODY. The type of MODY inherited will depend on the gene responsible and are labelled as MODY 1 to MODY 5.
The 5 genes identified are:
Why is it useful to recognize MODY?
To decide on appropriate treatment.
Knowing the type of MODY will help predict how diabetes is going to progress.
To advise other family members on risk of inheriting the condition and passing it on.
How is MODY treated?
Just like type 2 diabetes with diet and exercise. Sometimes, tablets or insulin are required
A prospective study of MODY and risk of coronary heart disease and stroke in women. Channing Laboratory, Department of Medicine, Harvard Medical School, Boston,
Permanent, neonatal diabetes mellitus is a rare disorder, occurring in about one in 400,000 live births. Neonatal diabetes is when at birth, a baby does not secrete any insulin.
Mitochondrial diseases are very numerous and different. Apart from diseases definitely caused by abnormalities in mitochondrial DNA, many diseases are suspected to be caused in part by dysfunction of mitochondria, such as diabetes mellitus, forms of cancer and cardiovascular disease, lactic acidosis, specific forms of myopathy, osteoporosis, Alzheimer's disease, Parkinsons's disease, stroke, and many more
Both type 1 and type 2 diabetes are at least partly inherited. Type 1 diabetes appears to be triggered by infection, stress, or environmental factors (e.g. exposure to a causative agent). There is a genetic element in the susceptibility of individuals to some of these triggers which has been traced to particular HLA genotypes (i.e. genetic "self" identifiers used by the immune system). However, even in those who have inherited the susceptibility, type 1 diabetes mellitus seems to require an environmental trigger. A small proportion of type 1 diabetics carry a mutation that causes maturity onset diabetes of the young (MODY).
Fajans SS, 1990. Scope and heterogeneous nature of MODY. Diab Care 13:49-64. For historical perspective, this review covers the concept just before the nature of the first of the specific molecular defects was discovered. It illustrates the significant change in the disease(s) referred to as MODY before and after 1990.
Fajans SS, Bell GI, Polonsky, 2001. Mechanisms of disease: molecular mechanisms and clinical pathophysiology of maturity-onset diabetes of the young. New Engl J Med 345:971-80. An excellent overview of the modern concept of the 6 types of MODY.
Hattersley A, Gloyn A, Pearson E, Edgehill E, Flanagan S, Ellard S. Novel monogenic diabetes results from activating mutations in Kir6.2 Presented at the First Meeting for the European Group for the Study of Monogenic Diabetes ("MODY in Malaga"); Malaga, Spain, 21 October 2004. Published form should be available in 2005.
Dean L and McEntyre J, 2004. The Genetic Landscape of Diabetes. Bethesda:NCBI, 2004. This is an entire online textbook on the complex genetics of the forms of diabetes. The chapter on MODY provides an up-to-date and concise overview of the molecular defects. Little expansion of clinical knowledge of the 6 types since 2001 has occurred.
Important Medical Disclaimer
All material found on this site is intended for general informational purposes only. This site should not be used for self- diagnosis or as a substitute for professional medical care. IOH recommends that you seek the advice of a competent health professional for diagnosis and treatment options, or before making any changes to your current diabetes care plan.
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Maturity Onset Diabetes of the Young (MODY)
What is Maturity Onset Diabetes of the Young (MODY)
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.
In 1992, Graeme Bell, the Louis Block Professor in Biochemistry & Molecular Biology, Medicine and Human Genetics, led a team that discovered that glucokinase mutations were one cause of a sub-type of diabetes called maturity onset diabetes of the young, or MODY. According to Bell, that defect appears to be relatively common and underdiagnosed.
MODY is a type of diabetes that has six basic sub classifications depending upon the gene that contributed onset (there may be more, but so far, only six genes have been identified in MODY). Only 1-2% of type 1 diabetics have this form of diabetes but it often goes unrecognized. MODY is an autosomal dominantly inherited disease, which means that it is inherited by a single (auto) gene which can come from either parent. When a parent has MODY their children have a 50% chance of also developing MODY.
The three main identifying characteristics of MODY are:
Identifying which form of MODY a person has is key to ensuring proper treatment. Hepatic Nuclear Factor 1 Alpha (HNF1-a) accounts for approximately 70% of all diagnosed cases of MODY. Other genes currently known to be involved are HNF4-a, IPF1, and Neuro D1. Two other forms of MODY affect the genes Glucokinase, and RCAD (Renal Cysts And Diabetes), a newly described familial cystic kidney syndrome associated with mutations in the hepatocyte nuclear factor-1ß gene.
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 (see sidebar) 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 KATP channel forms of MODYX.
The following characteristics should warrant consideration of a diagnosis of MODY in hyperglycemic and diabetic patients:
The 6 recognised forms of MODY are all due to ineffective insulin production or release by pancreatic β-cells. Five of the 6 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).
Genetics & Subtypes of MODY
They are inherited in an autosomal dominant fashion, and most patients therefore have other members of the family with diabetes; penetrance differs between the types (from 40% to 90%).
MODY 1: hepatocyte nuclear factor 4α
MODY 1 is due to a loss-of-function mutation in the HNF4α gene on chromosome 20 that codes for transcription factor 14 (TCF14). HNF4α controls function of HNF1α (see MODY 3) and perhaps HNF1β (MODY 5) as well. This transcription network plays a role in the early development of the pancreas, liver, and intestines. In the pancreas these genes influence expression of, among others, the genes for insulin, the principal glucose transporter (GLUT2), and several proteins involved in glucose and mitochondrial metabolism.
Although pancreatic beta cells produce adequate insulin in infancy, the capacity for insulin production declines thereafter. Diabetes (persistent hyperglycemia) typically develops by early adult years, but may not appear until later decades. The degree of insulin deficiency is slowly progressive. Many patients with MODY 1 are treated with sulfonylureas for years before insulin is required.
Liver effects are subtle and not clinically significant. Many people with this condition have low levels of triglycerides, lipoprotein(a), apolipoproteins AII and CIII.
There is an incompletely understood linkage of some of these genes with familial type 2 diabetes as well.
MODY 2: glucokinase
MODY 2 is due to any of several mutations in the GCK gene on chromosome 7 for glucokinase. Glucokinase serves as the glucose sensor for the beta cell. Normal glucokinase triggers insulin secretion as the glucose exceeds about 90 mg/dl (5 mM). These loss-of-function mutations result in a glucokinase molecule that is less sensitive or less responsive to rising levels of glucose. The beta cells in MODY 2 have a normal ability to make and secrete insulin, but do so only above an abnormally high threshold (e.g., 126-144 mg/dl, or 7-8 mM). This produces chronic, mild hyperglycemia which is usually asymptomatic. It is usually detected by accidental discovery of mild hyperglycemia (e.g., during pregnancy screening). An oral glucose tolerance test is much less abnormal than would be expected from the impaired (elevated) fasting glucose, since insulin secretion is usually normal once the glucose has exceeded the threshold for that specific variant of the glucokinase enzyme. It can usually be controlled by dietary measures (primarily avoiding large amounts of carbohydrate). The degree of hyperglycemia does not usually worsen with age and long-term diabetic complications are rare.
This type of MODY demonstrates the common circulation but complex interplay between maternal and fetal metabolism and hormone signals in the determination of fetal size. Because MODY2 is an autosomal dominant condition, an affected mother will pass it to 50% of her children. A small number of infants will have a new mutation not present in their mothers. If the mother is affected and the fetus is not, the maternal glucose will be somewhat high and the normal pancreas of the fetus will make lots of insulin, resulting in a large infant. If the fetus is affected but mother is not, glucoses will be normal and fetal insulin production will be low, resulting in intrauterine growth retardation. Finally, if both mother and fetus have the disease, the two defects will offset each other and fetal size will be unaffected.
MODY 3: hepatocyte nuclear factor 1α
MODY 3 is caused by mutations of the HNF1α gene, a homeobox gene on chromosome 12. This is the most common type of MODY in populations with European ancestry, accounting for about 70% of all cases in Europe. HNF1α is a transcription factor (also known as transcription factor 1, TCF1) that is thought to control a regulatory network (including, among other genes, HNF1α) important for differentiation of beta cells. Mutations of this gene lead to reduced beta cell mass or impaired function. MODY 1 and MODY 3 diabetes are clinically similar. About 70% of people develop this type of diabetes by age 25 years, but it occurs at much later ages in a few. This type of diabetes can often be treated with sulfonylureas with excellent results for decades. However, the loss of insulin secretory capacity is slowly progressive and most eventually need insulin.
This is the form of MODY which can most resemble ordinary type 1 diabetes, and one of the incentives for diagnosing it is that insulin may be discontinued or deferred in favor of oral sulfonylureas. Some people treated with insulin for years due to a presumption of type 1 diabetes have been able to switch to pills and discontinue injections. Long-term diabetic complications can occur if the glucose is not adequately controlled.
MODY 4: insulin promoter factor-1
MODY 4 arises from mutations of the IPF1 homeobox gene on chromosome 13. IPF1 is a transcription factor vital to the development of the embryonic pancreas. Even in adults it continues to play a role in the regulation and expression of genes for insulin, GLUT2, glucokinase, and somatostatin.
MODY 4 is so rare that only a single family has been well-studied. A child born with pancreatic agenesis (absence of the pancreas) was found to be homozygous for IPF1 mutations. A number of older relatives who were heterozygous had mild hyperglycemia or diabetes. None were severely insulin-deficient and all were controlled with either diet or oral hypoglycemic agents.
MODY 5: hepatocyte nuclear factor 1β
HNF1β-related MODY is one of the less common forms of MODY, with some distinctive clinical features, including atrophy of the pancreas and several forms of renal disease. HNF1β, also known as transcription factor 2 (TCF2), is involved in early stages of embryonic development of several organs, including the pancreas, where it contributes to differentiation of pancreatic endocrine Ngn3+ cell progenitors from non-endocrine embryonic duct cells. The gene is on chromosome 17.
The degree of insulin deficiency is variable. Diabetes can develop from infancy through middle adult life, and some family members who carry the gene remain free of diabetes into later adult life. Most of those who develop diabetes show atrophy of the entire pancreas, with mild or subclincal deficiency of exocrine as well as endocrine function.
The non-pancreatic manifestations are even more variable. Kidney and genitourinary malformation and diseases may occur, but inconsistently even within a family, and the specific conditions include a range of apparently unrelated anomalies and processes. The most common genitourinary condition is cystic kidney disease, but there are many varieties even of this. Renal effects begin with structural alterations (small kidneys, renal cysts, anomalies of the renal pelvis and calices), but a significant number develop slowly progressive renal failure associated with chronic cystic disease of the kidneys. In some cases, renal cysts may be detected in utero. Kidney disease may develop before or after hyperglycemia, and a significant number of people with MODY5 are discovered in renal clinics.
With or without kidney disease, some people with forms of HNF1β have had various minor or major anomalies of the reproductive system. Male defects have included epididymal cysts, agenesis of the vas deferens, or infertility due to abnormal spermatozoa. Affected women have been found to have vaginal agenesis, hypoplastic, or bicornuate uterus.
Liver enzyme elevations are common, but clinically significant liver disease is not. Hyperuricaemia and early onset gout have occurred.
MODY 6: neurogenic differentiation 1
MODY 6 arises from mutations of the gene for the transcription factor referred to as neurogenic differentiation 1. The gene is on chromosome 2 in a region of the p arm known as IDDM7 because it includes genes affecting susceptibility to type 1 diabetes. NeuroD1 promotes transcription of the insulin gene as well as some genes involved in formation of beta cells and parts of the nervous system.
This is also one of the rarer forms of MODY. Only 3 kindreds with mutations causing MODY6 have been identified so far. In both, some of the members had more typical type 2 diabetes rather than MODY, and the reasons for the difference of expression have not been worked out. Most of the family members with diabetes were diagnosed after age 40, but a few required insulin for blood sugar control.
MODY X: other possible forms of MODY
The known 6 types described above account for about 85-90% of cases identified by clinical criteria, suggesting that there are other forms and causes still to be identified.
The strongest candidate for inclusion as a new form of monogenic diabetes is the neonatal diabetes caused by activating mutations of the KCNJ11 gene, which codes for the Kir6.2 subunit of the beta cell KATP channel. This results in congenital impairment of insulin release. The insulin deficiency results in poor prenatal growth and intrauterine growth retardation. The diabetes is usually diagnosed in the first few months of life. Remarkably, this type of diabetes often responds well to sulfonylureas and insulin may not be necessary.
Complications and Goals of Management
Unfortunately, chronic hyperglycemia of 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 long-term diabetes.
Tools available for management are also those available 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. 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).
Related Homozygous Disorders
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, a small number of people carrying two abnormal alleles have been identified. Unsurprisingly, combined (homozygous) defects of these genes are both much rarer and much more severe in their effects.
Homozygous HNF4α, HNF1α, HNF1β, and NeuroD1 mutations have not yet been described. Those mutations for which a homozygous form has not been described may be extremely rare, or 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.
Page Updated 12/14/2005