Alternative Names
Diabetes mellitus; "sugar"; type I diabetes; type II diabetes
Symptoms & Characteristics
Diabetes is a disease in which blood glucose (sugar) levels are too high. Glucose is obtained through diet. Insulin is a hormone that is needed to convert sugar and other foods into energy needed for daily life. When the body does not produce or properly use insulin, sugar cannot be used and gets too high. There are many different types of diabetes. Here are some of the major types:
- Type 1 diabetes results when the body does not produce insulin. Type 1 diabetes is usually diagnosed in non-obese children.
- Type 2 diabetes results when the body is resistant to the effects of insulin and/or the body produces some, but not enough, insulin to maintain normal glucose levels. Type 2 diabetes is usually diagnosed in adulthood and is associated with obesity and lack of exercise.
- MODY (maturity-onset diabetes of the young) results when the body produces less insulin than normal but still has some partial insulin production. MODY is typically diagnosed before 25 years old and is often misdiagnosed as type 1 or type 2 diabetes.
- Neonatal diabetes mellitus can be permanent or transient (goes away) and is characterized by an onset of symptoms within the first six months of life. Some individuals with transient neonatal diabetes mellitus develop type 2 diabetes later in life.
- Gestational diabetes occurs in some pregnant women who did not have diabetes before pregnancy. Gestational diabetes usually resolves after pregnancy but may increase the risk to develop type 2 diabetes later in life.
Some common signs and symptoms of diabetes include:
- numbness or tingling in the feet
Over time, high blood sugar levels can cause severe damage to eyes, kidneys and nerves; as well as cause heart disease, stroke and even the need to amputate limb(s).
Treatment
A specific blood test can determine if a person has diabetes. Treatment and routine monitoring of blood glucose levels can help to manage some of the symptoms and sometimes prevent related problems.
Pregnant women with diabetes, who have been diagnosed before 25 weeks gestation, are at an increased risk to develop pregnancy complications as well as to have a baby with certain birth defects. It is always important to speak with a doctor regarding the appropriate care and management of diabetes before and during pregnancy.
How Common Is It?
Over 20 million people are believed to be affected with diabetes in the United States.
- About 10% to 15% of people with diabetes have type 1diabetes.
- Most Americans with diabetes have type 2 diabetes.
- Neonatal diabetes is rare and affects about 1 in 400,000 newborns.
- About 4% of all pregnant women are believed to be affected with gestational diabetes.
Genetics & Inheritance
The genetics of diabetes differs by type.
Type 1 diabetes and Type 2 diabetes:
Type 1 and Type 2 diabetes are both multifactorial conditions, which means they involve a combination of genetic, lifestyle and environmental factors.
- Some non-genetic factors that have been proposed to influence type 1 diabetes risk include living in a cold climate, exposure to certain viruses, and not being breastfed as an infant.
- Some non-genetic factors that have been proposed to influence type 2 diabetes risk include obesity, lack of exercise, and a diet high in sugar.
Researchers believe that there are a number of genes that influence susceptibility to type 1 and type 2 diabetes.
Single nucleotide polymorphisms (or SNPs) are small variations in a single "letter" of DNA that can be found throughout our entire genetic make-up. Specific SNPs located at numerous sites (more than a dozen so far) within the genome have been associated with susceptibility to type 1 or type 2 diabetes. However, the increased risk to develop diabetes associated with these SNPs is considered relatively small at this point. Further research is needed to replicate study findings and clearly establish associations.
People who have certain genetic conditions, such as hemochromatosis or mitochondrial conditions, are at an increased risk to develop diabetes.
Other yet to be identified or adequately classified genes may also contribute to type 1 and type 2 diabetes risk.
MODY:
MODY is an inherited genetic condition. There are currently nine identified types of MODY called MODY1-MODY9, which are caused by mutations in nine different genes.
MODY2 and MODY3 are the most common forms of MODY in Caucasians.
In the different types of MODY, having a mutation in a single gene copy is sufficient enough to cause the disease. This is called autosomal dominant inheritance. An affected person has a 50% chance to have an affected child with each pregnancy.
Neonatal diabetes mellitus:
In about 50% of cases of neonatal diabetes mellitus, diabetes is transient and resolves at a median age of 3 months. Transient neonatal diabetes mellitus has been associated with the overexpression of two genes, PLAGL1(ZAC) and HYMAI, found within an imprinted gene region at 6q24, as well as mutations in the KCNJ11 or ABCC8 genes. In transient neonatal diabetes caused by mutations in either the KCNJ11 or ABCC8 gene, having a mutation in a single gene copy is sufficient to cause the disease. This is called autosomal dominant inheritance.
The other 50% of cases of neonatal diabetes mellitus are permanent. Permanent neonatal diabetes mellitus (PNDM) can occur alone (isolated) or as part of a larger genetic syndrome. Isolated PNDM has been associated with mutations in at least five genes. These genes are KCNJ11 (about 30% of cases), ABCC8 (about 19% of cases), INS (about 20% of cases), GCK (about 4% of cases), and PDX1 (<1% of cases). Syndromic cases are caused by mutations in different genes.
- About 20% of people with mutations in the KCNJ11 gene have associated neurological features called DEND syndrome (developmental delay, epilepsy, and neonatal diabetes mellitus). Intermediate DEND syndrome refers to a milder form of the condition without seizures and with less severe developmental delay.
In PNDM caused by mutations in KCNJ11 or INS, one copy of the altered gene in each cell is sufficient to cause the condition. This is called autosomal dominant inheritance. While some cases of autosomal dominant PNDM are inherited from an affected parent, most cases occur due to a new, sporadic ("de novo") mutation in people with no family history of the disorder. Affected people have a 50% chance to have an affected child with each pregnancy.
In PNDM caused by mutations in GCK or PDX1 (and some cases caused by mutations in ABCC8), both copies of the gene in each cell have mutations. This is called autosomal recessive inheritance. Both parents of an affected person are obligate carriers (each have only one mutation). Two carriers have a 25% chance with each pregnancy to have an affected child, but typically do not have symptoms themselves. However, carriers for mutations in GCK may have MODY2.
Gestational diabetes:
The causes of gestational diabetes are largely unknown.
Researchers believe that having a family history of either type 1 or type 2 diabetes may increase the risk to develop gestational diabetes.
Genetic Testing
Clinical genetic testing for susceptibility to type 1 diabetes, type 2 diabetes or gestational diabetes is currently unavailable. Clinical genetic testing for MODY or neonatal diabetes mellitus may be available through an in person genetic consultation for people who are considered at risk. For more information on the genetics of diabetes: use our find a genetic professional directory to locate a trained
genetic professional in your area.
Informational genetic testing for susceptibility to type 1 and type 2 diabetes is available online (over the internet) as part of a whole genome scan. Whole genome scanning involves analyzing thousands of SNPs at once related to a number of different health conditions.
- At this point, many genetic professionals do not consider this testing clinically useful or medically relevant, but for informational purposes only. Go to the Tests tab to link to online providers, compare providers and read provider reviews.
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Last Reviewed February 2, 2010