OVERVIEW

What is Maturity-Onset Diabetes of the Young?

Maturity-onset diabetes of the young (MODY), also known as "adult-onset diabetes in youth," "youth-onset adult-type diabetes," or other similar terms, is directly translated from English, leading to various names—though the abbreviation remains the same: MODY.

MODY is a familial, inherited form of diabetes with the following key characteristics:

• It typically develops before the age of 25;

• At least three consecutive generations in the immediate family have diabetes (e.g., the patient, their father, and their grandfather);

• Its symptoms and manifestations resemble type 2 diabetes, usually without ketoacidosis, and insulin therapy is generally unnecessary for at least the first two years after onset.

Is Maturity-Onset Diabetes of the Young Common?

Monogenic diabetes, unlike type 1 or type 2 diabetes, is not as prevalent. It is a rare form of diabetes caused by genetic mutations. International data suggest that MODY accounts for approximately 1–3% of all diabetes cases.
Although the proportion of MODY is relatively low, China's large population and high diabetes prevalence make this a significant number that cannot be overlooked.
Currently, very few MODY cases have been reported in China, likely because most cases are mild and easily missed or misdiagnosed as type 1 or type 2 diabetes.

SYMPTOMS

What are the manifestations of Maturity-Onset Diabetes of the Young (MODY)?

The typical manifestations of Maturity-Onset Diabetes of the Young (MODY) include:

• Elevated blood sugar levels before the age of 25, though usually mild;

• Normal or lean body weight at onset;

• Absence of obvious symptoms such as dry mouth, excessive thirst, frequent urination, increased appetite, or weight loss. Due to the lack of noticeable symptoms and infrequent blood sugar testing in young people, many MODY cases are diagnosed in middle age or later;

• Rare occurrence of acute diabetic complications like ketoacidosis;

• No need for insulin therapy within at least the first two years of onset;

• A strong family history of diabetes, with affected relatives often developing the condition at a young age.

Depending on the mutated gene, MODY can be classified into several subtypes, such as MODY1, MODY2, MODY3...MODY6. Different subtypes vary in severity and clinical manifestations.

What other diseases can Maturity-Onset Diabetes of the Young (MODY) cause?

The complications of MODY are similar to those of typical diabetes, including diabetic retinopathy, diabetic nephropathy, and diabetic peripheral vascular disease.
MODY2 patients generally have milder conditions and rarely develop complications like hypertension, obesity, or hyperlipidemia. Even if complications occur, they are usually mild.
MODY1 and MODY3 patients often experience more severe conditions, with a higher risk of diabetic retinopathy and nephropathy as the disease progresses. Eventually, about half of these patients require insulin therapy for blood sugar control.
MODY5 patients frequently present with polycystic kidneys, renal glycosuria, non-diabetic kidney disease, and renal dysfunction. Female patients may also exhibit genital developmental abnormalities.

CAUSES

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

The cause of maturity-onset diabetes of the young (MODY) is abnormal familial genes. These abnormal familial genes can lead to reduced insulin secretion, resulting in elevated blood sugar levels.

Is maturity-onset diabetes of the young hereditary?

Maturity-onset diabetes of the young (MODY) is a special type of diabetes caused by a single gene mutation and is directly inheritable.
The inheritance pattern is "autosomal dominant," meaning that only one chromosome in a pair needs to carry the mutated gene for the disease to manifest.
In most MODY patients, one chromosome carries a "normal" gene, while the other carries the mutated gene. For such patients, the probability of their children inheriting MODY is 50%. If their children do not inherit the mutated gene, they will not develop MODY, and their descendants will also not develop MODY (unless they marry another MODY patient).

DIAGNOSIS

What tests are needed for adult-onset diabetes in adolescents?

The tests are the same as for general diabetes, including blood glucose, glycated hemoglobin, liver and kidney function, fundus examination, urine protein, diabetes autoantibodies, insulin, C-peptide, etc.
In addition, genetic testing for patients suspected of having maturity-onset diabetes of the young (MODY) can confirm the diagnosis of MODY.

How to distinguish between adult-onset diabetes in adolescents and type 1 or type 2 diabetes?

See the table below for details, referenced from "Clinical Endocrinology" edited by Chen Jialun.

TREATMENT

Which department should adolescents with adult-onset diabetes generally visit?

Endocrinology department.

How is adult-onset diabetes in adolescents treated?

The overall treatment principles for MODY are the same as for ordinary diabetes, which include controlling blood sugar and preventing or delaying complications. Treatment is usually lifelong.
Of course, different MODY subtypes require different blood sugar control strategies. For example:

• MODY2 is generally mild, with two-thirds of patients able to control blood sugar through diet and moderate exercise without medication. The remaining one-third can achieve good blood sugar control with oral hypoglycemic drugs. If pregnancy is planned, short-term insulin use may be required during pregnancy to control blood sugar.

• MODY1 and MODY3 are usually more severe. In the early stages, oral hypoglycemic drugs are needed to control blood sugar. As the condition progresses, about half of the patients will eventually require insulin.

Common oral hypoglycemic drugs include sulfonylureas (e.g., Glibenclamide) and α-glucosidase inhibitors (e.g., Acarbose).

Do adolescents with adult-onset diabetes need follow-up examinations? How often should they be done?

Yes, follow-up examinations are necessary. If blood sugar control is poor, frequent check-ups as advised by the doctor are required. If blood sugar remains stable, follow-ups can be scheduled every 1–3 months. Diabetic patients should learn to monitor their fingertip blood sugar at home.

DIET & LIFESTYLE

What should adolescents with adult-onset diabetes pay attention to in their diet?

Click to view related entries: Lifestyle precautions for diabetes, Diabetes dietary guidelines, for relevant content.

What should adolescents with adult-onset diabetes pay attention to in daily life?

• Control diet, eat on time, and avoid overeating.

• Engage in appropriate exercise to maintain body shape.

• Guard against hypoglycemia, carry biscuits and candies, and promptly measure blood sugar and eat when symptoms such as hunger, palpitations, sweating, dizziness, or hand tremors occur.

• Learn to self-test blood sugar, monitor blood sugar regularly, and inform the doctor about blood sugar levels during follow-up visits.

Does adolescent adult-onset diabetes affect fertility?

MODY itself does not affect fertility. Even more severe types like MODY1 and MODY3 allow for childbirth, though insulin may be needed to control blood sugar during pregnancy.
However, patients are highly likely to pass MODY to their offspring. Therefore, it is recommended that MODY patients seek genetic counseling before planning pregnancy, discuss the likelihood and health impact of the condition in their children with professional doctors, and decide on optimal reproductive strategies.

Does adolescent adult-onset diabetes affect daily activities?

As long as blood sugar is well-controlled and no diabetes complications have occurred, it generally does not affect exercise, high-altitude travel, or flying. However, be mindful of potential hypoglycemia and carry candies and biscuits.

PREVENTION

How to Prevent Adult-Onset Diabetes in Adolescents?

Before planning to conceive, MODY patients should seek genetic counseling and discuss the risk of their offspring inheriting the condition with a specialist to decide whether to have children. If there is a MODY patient in the family, other healthy members can undergo genetic testing. If they carry MODY-causing genes, early lifestyle interventions and blood glucose monitoring can be implemented, potentially preventing the onset of MODY.