People with this form of diabetes have GAD antibodies. Testing for these can help diagnose the type of diabetes an adult has.
What are GAD antibodies?
GAD antibodies stop insulin being produced in the pancreas by marking out cells for attack.
GADA is short for GAD autoantibodies. Antibodies in this case means autoantibodies.
GAD antibodies result in the immune system stopping insulin being produced, leading to diabetes.
Normal role of GAD
GAD is short for glutamic acid decarboxylase. This is an enzyme that is needed to make a neurotransmitter. Neurotransmitters are involved in nerve messaging.
The neurotransmitter is gamma-aminobutyric acid (GABA), an amino acid that has the effect of reducing nerve transmission.
GAD inhibits nerve messages. It relaxes muscles, for example. Lack of GAD is involved in a disease known as stiff-person syndrome.
GAD is found in the brain and the pancreas, the organ in the belly that produces insulin.
When GAD produces antibodies
Unfortunately, GAD can also act as an autoantigen. This means that it triggers the immune system to produce antibodies against its own cells.
In this case, these GAD autoantibodies mark out cells in the pancreas for attack.
These pancreas cells produce insulin. Diabetes is the result of the immune system attacking these cells as if they were foreign material that must be destroyed.
Autoimmunity is the cause of type 1 diabetes, and other diabetes-related autoantibodies are also involved aside from GAD autoantibodies.
Finding GAD antibodies is a way to diagnose type 1 diabetes when doctors are not sure. This may be when people show signs in later life that start to resemble type 1 diabetes, whereas type 1 usually develops at younger ages.
What is LADA?
LADA stands for latent autoimmune diabetes in adults. It can be considered slow-developing type 1 diabetes. It usually appears after the age of 30.
LADA is a condition in people later in adulthood who develop what might appear at first to be type 2 diabetes. In fact, the condition is more similar to type 1 diabetes. It has been called "type 1.5 diabetes."
Adults with diabetes who are positive for the GAD autoantibodies are more likely to need insulin treatment. A need for insulin at the time of diagnosis defines type 1 diabetes. It is usually diagnosed in late childhood.
LADA usually requires insulin treatment within 6 to 12 months of a GADA-positive test.
Symptoms of diabetes
High thirst may be one symptom of diabetes.
Classic diabetes symptoms include:
- Needing to urinate often
- High thirst
- Unusual hunger
- Lack of energy
- Blurry vision
These symptoms are caused by high levels of sugar in the blood. They are often what lead to a diagnosis of diabetes. The symptoms are reduced by treatment.
Some other symptoms, such as tingling or numbness in the feet or hands, can signal advanced disease caused by diabetes.
Some symptoms are more typical of type 1 diabetes than type 2 diabetes, such as unusual weight loss.
Type 1 diabetes and GAD antibodies
Most people with diabetes have type 2 diabetes, which usually develops in adult life.
Type 1 diabetes is less common and usually has an onset in children and young adults. If the diagnosis of type 1 or 2 diabetes is unclear, a test for GAD antibodies can help.
How is a GAD antibody test done?
A test for GAD antibodies is done by scientists working in a lab. The sample they test is from the blood. The sample may also be used for other diabetes tests done at the same time.
Taking the blood sample involves a needle through the skin, usually in the arm, to reach a vein and draw blood. The small wound may be mildly painful afterward.
What do GAD antibody results mean?
The GAD antibody test comes back with a measurement of the level of GADA in the blood:
- If the result is equal to or below 0.02 nanomoles per liter, this diagnoses type 1 diabetes
- Higher concentrations above 0.03 nanomoles per liter signal nervous disorders
Other tests for diabetes
Testing for GAD antibodies is not routine for people suspected of having diabetes.
It is used when there is doubt about whether the condition is type 1 or type 2 diabetes. Other antibodies are also tested during this lab diagnosis:
- Islet cell cytoplasmic autoantibodies (ICA) - these antibodies also result in insulin-producing cells being attacked
- Insulinoma-associated-2 autoantibodies
- Insulin autoantibodies - insulin itself can trigger an attack by the immune system
Standard tests for diabetes are usually enough to make a diagnosis of type 1 or type 2 diabetes. Both kinds involve measurement of blood sugar levels.
The decision to diagnose type 1 or 2 is usually made based on features such as age of onset, severity of symptoms, and need for insulin.
Blood sugar levels are tested in the blood sample. This can measure the concentration indicated at the time of the sample. The A1C test indicates the average blood sugar level over the previous 3 months.
What other conditions result in high GAD antibodies?
Injecting insulin works to control blood sugar levels.
Autoimmunity against the neurotransmitter targeted by GAD antibodies results in a nerve disorder known as stiff-person syndrome.
This condition is uncommon but happens more often in people with other autoimmunity disorders, including type 1 diabetes.
Symptoms of stiff-person syndrome include:
- Muscle stiffness
- Muscle spasms
The symptoms progress slowly. They affect the trunk mostly, but also the limbs.
The level of GAD antibodies is typically higher in people who have stiff-person syndrome than in people who have type 1 diabetes.
Treatment of type 1 diabetes
Type 1 diabetes caused by autoimmunity needs to be treated by providing the insulin that cannot be produced by the body.
Treatment is not targeted at the autoimmune aspect caused by GAD autoantibodies. Instead, it treats the problem caused by it.
Insulin treatment controls blood sugar levels. This prevents complications caused by high blood sugar, which causes damage to blood vessels.
People with type 1 diabetes, including people with LADA, must manage their condition with daily blood tests and insulin injections.
Insulin may also be needed to treat type 2 diabetes in its later stages. Type 2 diabetes does not involve the attack of insulin-producing cells led by GAD antibodies, however.