Maturity-Onset Diabetes of the Young

What is maturity-onset diabetes of the young?

Maturity-onset diabetes of the young, often shortened to MODY, is a rare, inherited form of diabetes caused by a change in a single gene. Diabetes is a condition in which the level of glucose (sugar) in the blood is too high because the body cannot produce or use insulin properly. Insulin is the hormone made by the pancreas that lets glucose move from the blood into the body’s cells.

Most people with diabetes have type 1 or type 2. Maturity-onset diabetes of the young is different from both. It does not involve the immune system attacking the pancreas, as happens in type 1 diabetes, and it is not primarily driven by excess body weight and insulin resistance, as is typical in type 2 diabetes. Instead, one altered gene reduces the ability of the pancreas to sense glucose or release insulin normally.

The name can be confusing. “Maturity-onset” was chosen decades ago because the condition looked like adult-type diabetes, and “of the young” because it appears early in life, often in adolescence or young adulthood. Today, doctors more often use the term monogenic diabetes, meaning diabetes caused by one gene. MODY is thought to account for a small share of all diabetes cases, and many people who have it are initially told they have type 1 or type 2 diabetes. Because a correct diagnosis can change treatment, hospitals usually manage this condition within an endocrinology department, such as the Endocrinology & Metabolism unit at Acibadem.

MODY typically runs in families. A parent with the altered gene has a one-in-two chance of passing it to each child, regardless of the child’s sex. Several genes can cause the condition, and each gene produces a somewhat different pattern of blood glucose, complications, and response to medication.

Symptoms of maturity-onset diabetes of the young

Maturity-onset diabetes of the young symptoms depend heavily on which gene is affected. Some forms cause only mildly raised blood glucose that produces no symptoms at all and is discovered by chance during a routine blood test. Other forms cause blood glucose to rise gradually over years, eventually leading to the classic signs of diabetes.

When symptoms do occur, they may include:

• Passing urine more often than usual, including at night
• Increased thirst and a dry mouth
• Feeling more tired than usual
• Blurred vision
• Recurrent infections, such as thrush or urinary tract infections
• Slow-healing cuts or sores
• Unintended weight loss, although this is less common than in type 1 diabetes
• Glucose detected in the urine even when blood glucose is only mildly raised (a feature of some subtypes)

How these signs appear often differs by subtype. In the form caused by a change in the glucokinase gene (often called GCK-MODY), fasting blood glucose is mildly raised from birth, remains fairly stable throughout life, and rarely causes symptoms. In forms linked to the HNF1A and HNF4A genes, blood glucose is often normal in early childhood and then rises through the teenage years and twenties, so symptoms tend to emerge gradually in that age range. In the HNF1B form, diabetes may be accompanied by kidney abnormalities, such as cysts, that are sometimes detected before any blood glucose problem.

Unlike type 1 diabetes, people with MODY usually do not develop diabetic ketoacidosis, a dangerous build-up of acids in the blood, at the time of diagnosis, because their pancreas still produces some insulin. Unlike typical type 2 diabetes, many people with MODY are not overweight and do not show signs of insulin resistance, such as darkened skin folds or high blood pressure, at a young age. These differences are part of what prompts doctors to consider a monogenic cause.

Causes and risk factors

Maturity-onset diabetes of the young causes come down to a single altered gene that affects how the beta cells of the pancreas work. Beta cells are the cells that make and release insulin. More than a dozen genes have been linked to MODY, but a few account for the large majority of cases:

• HNF1A — one of the most common causes. Insulin production declines progressively from adolescence onward. People with this form often have a low kidney threshold for glucose, meaning sugar appears in the urine at relatively modest blood glucose levels.
• GCK (glucokinase) — the glucokinase enzyme acts as the pancreas’s glucose sensor. When it is altered, the body “resets” its target blood glucose slightly higher than normal. The result is mild, stable, lifelong hyperglycemia (high blood glucose) that generally does not worsen over time.
• HNF4A — similar in course to HNF1A. Babies who inherit this change are often large at birth and may have low blood glucose in the newborn period before developing diabetes later in life.
• HNF1B — associated with kidney cysts and other kidney or urinary tract abnormalities, and sometimes with problems in the liver, pancreas, or reproductive organs. Diabetes in this form may require insulin earlier than in other types.

Other, rarer gene changes exist, and in some families the responsible gene has not yet been identified.

MODY is inherited in an autosomal dominant pattern. This means a person needs only one copy of the altered gene, from either parent, to develop the condition. In many cases the gene can be traced back through several generations. Occasionally the change arises for the first time in a child (a new or “de novo” variant), in which case there is no earlier family history.

Because the cause is genetic rather than lifestyle-related, the risk factors for maturity-onset diabetes of the young are different from those for type 2 diabetes:

• Having a parent with MODY or with diabetes diagnosed at a young age
• Diabetes affecting multiple generations of the family
• Diabetes diagnosed before about age 25 to 35
• Not being overweight at the time of diagnosis
• Absence of the antibodies that mark type 1 diabetes
• A family history of kidney cysts (relevant to the HNF1B form)
• A personal or family history of unusually large birth weight or newborn low blood glucose (relevant to the HNF4A form)

Diet, exercise, and body weight do not cause MODY, although they can still influence how well blood glucose is controlled once the condition is present.

Diagnosis of maturity-onset diabetes of the young

Maturity-onset diabetes of the young diagnosis usually happens in two stages: first, doctors recognize that a person’s diabetes does not fit the typical picture of type 1 or type 2, and second, genetic testing confirms the specific gene involved.

Standard blood tests are used to establish that diabetes is present and to gauge its severity. These include a fasting blood glucose test, a hemoglobin A1c test (which reflects average blood glucose over roughly the preceding two to three months), and sometimes an oral glucose tolerance test, in which blood glucose is measured before and after drinking a sugary solution.

Doctors then look for clues that point away from type 1 or type 2 diabetes. Tests that help with this include:

• Diabetes autoantibody tests — these detect immune proteins that attack the pancreas in type 1 diabetes. In MODY they are usually negative.
• C-peptide measurement — C-peptide is a substance released alongside insulin, so it shows how much insulin the pancreas is still making. In type 1 diabetes it falls to very low levels within a few years; in MODY it often remains measurable long after diagnosis.
• Urine glucose testing — glucose in the urine at relatively modest blood glucose levels may suggest the HNF1A form.
• Kidney ultrasound — used when the HNF1B form is suspected, to look for cysts or structural abnormalities.
• Detailed family history — a family tree showing diabetes across generations strengthens the suspicion of a monogenic cause.

Some clinics use risk-assessment tools that combine age at diagnosis, body weight, family history, treatment history, and A1c to estimate how likely it is that a person has MODY and whether genetic testing is worthwhile.

The definitive test is genetic testing, usually performed on a blood or saliva sample. Laboratories may test the most common MODY genes together as a panel. A confirmed result identifies the exact gene and variant, which guides treatment and allows relatives to be offered testing. Genetic counseling is generally recommended before and after testing so that families understand what the results mean. It is worth noting that a negative genetic test does not completely rule out monogenic diabetes, because not all causative genes are known.

Treatment options for maturity-onset diabetes of the young

Maturity-onset diabetes of the young treatment is tailored to the specific gene involved, which is one of the main reasons an accurate diagnosis matters. There is no surgery or procedure for MODY itself; management centers on monitoring, medication where needed, and healthy lifestyle habits.

Observation and lifestyle measures. For the GCK form, blood glucose is mildly raised but stable, and long-term diabetes complications are uncommon. Many people with this form need no glucose-lowering medication at all. Doctors typically recommend regular check-ups and general healthy habits, such as a balanced diet and physical activity, rather than drug treatment. Medication is usually reserved for specific situations, such as pregnancy, where it may be considered depending on the baby’s growth.

Oral medication. People with the HNF1A and HNF4A forms are often very sensitive to a class of tablets called sulfonylureas, which stimulate the pancreas to release more insulin. In many cases, low doses of these tablets control blood glucose well, and some people who were previously started on insulin under a mistaken diagnosis of type 1 diabetes have been able to switch to tablets under medical supervision. Because these medications can cause low blood glucose (hypoglycemia), doses are started low and adjusted carefully. Other oral or injectable non-insulin medications may be considered if sulfonylureas are not suitable or stop working over time.

Insulin. Insulin injections may still be needed in some situations: when other treatments no longer keep blood glucose in the target range, in the HNF1B form (which often responds less well to tablets), during pregnancy, or during illness or surgery. Insulin is not a sign of treatment failure; it is simply the right tool for certain forms and stages of the condition.

Monitoring for complications. Like other forms of diabetes, MODY that leads to persistently high blood glucose can, over many years, damage the eyes, kidneys, nerves, and blood vessels. Routine eye examinations, urine and blood tests of kidney function, foot checks, and monitoring of blood pressure and cholesterol are part of standard care for most people with MODY, particularly those with the HNF1A, HNF4A, and HNF1B forms. People with the HNF1B form may also need ongoing care from a kidney specialist.

Family testing. Once a gene change is confirmed, first-degree relatives (parents, siblings, and children) may be offered genetic testing, even if they have no symptoms. Identifying affected relatives early can allow appropriate treatment and avoid unnecessary insulin or misdiagnosis.

Treatment decisions are individual. Your doctor may adjust the plan over time as you age, if you become pregnant, or if your blood glucose pattern changes.

Living with maturity-onset diabetes of the young and outlook

The long-term outlook for maturity-onset diabetes of the young varies by subtype. People with the GCK form generally have a very good outlook, with a low likelihood of diabetes-related complications, provided they attend regular reviews. For the HNF1A and HNF4A forms, the outlook depends largely on how well blood glucose is controlled over the years; with appropriate treatment and monitoring, many people maintain good health, although the risk of complications rises if glucose remains high for long periods. The HNF1B form carries additional considerations related to kidney function, and some people eventually develop reduced kidney function that requires specialist care.

Day to day, living with MODY often involves fewer demands than living with type 1 diabetes, particularly for people managed with tablets or with no medication. Many people still find it helpful to learn how food, activity, illness, and stress affect their blood glucose, and to check their glucose as advised by their care team. Because MODY is inherited, some families find it useful to talk with a genetic counselor about what the diagnosis means for children and future pregnancies.

Pregnancy deserves special planning. Blood glucose targets and treatment may change, and the baby may or may not inherit the gene, which can influence its growth in the womb. Women with MODY who are planning a pregnancy are generally advised to discuss this with their diabetes team beforehand.

Receiving a new or corrected diagnosis can bring mixed feelings, especially for people who have lived for years with a label of type 1 or type 2 diabetes. Support from diabetes educators, dietitians, and patient organizations can help. Ongoing care is typically coordinated by an endocrinologist, a doctor who specializes in hormone-related conditions, with input from other specialists as needed.

Frequently asked questions

What are the first maturity-onset diabetes of the young symptoms?

Many people have no symptoms at first, and mildly raised blood glucose is found on a routine test. When symptoms appear, they are usually the general signs of diabetes: increased thirst, passing urine more often, tiredness, and blurred vision. In some forms, glucose in the urine or a strong family history of early diabetes is the first clue rather than a symptom.

What are the main maturity-onset diabetes of the young causes?

MODY is caused by a change in a single gene that affects how the pancreas senses glucose or releases insulin. The most common genes involved are HNF1A, GCK, HNF4A, and HNF1B. The condition is inherited in a dominant pattern, so each child of an affected parent has a one-in-two chance of inheriting it. Lifestyle factors do not cause MODY.

How is maturity-onset diabetes of the young diagnosis confirmed?

Doctors first use standard blood tests to confirm diabetes and then look for features that do not fit type 1 or type 2, such as negative diabetes antibodies, preserved C-peptide, a young age at diagnosis, and diabetes across several generations. The diagnosis is confirmed by genetic testing on a blood or saliva sample, ideally with genetic counseling before and after.

What does maturity-onset diabetes of the young treatment involve?

Treatment depends on the gene involved. The GCK form often needs no medication, only monitoring. The HNF1A and HNF4A forms frequently respond well to low doses of sulfonylurea tablets, and insulin may be needed later or in specific situations. The HNF1B form may require insulin earlier and also involves monitoring kidney health. All forms benefit from healthy lifestyle habits and regular complication screening.

Can maturity-onset diabetes of the young be mistaken for type 1 or type 2 diabetes?

Yes, and this is common. Because MODY appears in young people, it is often assumed to be type 1; because it runs in families and does not cause ketoacidosis, it may be labeled type 2. Clues that should prompt a second look include negative antibodies, continued insulin production years after diagnosis, a normal body weight, and a parent diagnosed young.

Will my children inherit maturity-onset diabetes of the young?

Each child of a person with MODY has a one-in-two chance of inheriting the altered gene. Inheriting the gene generally means the child will develop the same form of the condition, although the age at which blood glucose rises varies. Genetic testing can be offered to children, usually after discussion with a genetic counselor about timing and implications.

Is maturity-onset diabetes of the young serious?

Seriousness varies by subtype. The GCK form is usually mild and rarely leads to complications. Other forms can cause the same long-term complications as other types of diabetes if blood glucose stays high, but with the right treatment and regular monitoring many people remain well. An accurate diagnosis is important because it allows treatment to be matched to the specific gene.

When to see a doctor

Consider arranging a medical review if you have been diagnosed with diabetes at a young age and it does not seem to fit a typical pattern, if several generations of your family have diabetes, or if a close relative has been found to have MODY. A review is also sensible if you are planning a pregnancy or if your blood glucose has become harder to control.

Seek urgent medical attention if you or a family member with diabetes develops any of the following:

• Severe or persistent vomiting, stomach pain, deep or rapid breathing, or a fruity smell on the breath, which can indicate diabetic ketoacidosis
• Confusion, extreme drowsiness, or difficulty staying awake
• Signs of severe low blood glucose, such as shaking, sweating, confusion, seizures, or loss of consciousness, especially in someone taking sulfonylureas or insulin
• Blood glucose readings that stay very high despite treatment, together with intense thirst and frequent urination
• Sudden loss of vision or new dark spots in the field of vision
• A foot wound that is not healing, is turning dark, or shows spreading redness, warmth, or discharge
• Chest pain, sudden weakness on one side of the body, or difficulty speaking

These signs may not be caused by MODY itself, but in anyone with diabetes they require prompt assessment.