Type 1.5 diabetes – a new diagnosis?

Dr Angela Murphy tells us about Type 1.5 diabetes, commonly known as latent autoimmune diabetes.


Mrs JM came to see me about her new diagnosis of Type 1.5 diabetes. She was concerned that she had never heard of this before and that it may represent a more dangerous type of diabetes. She specifically wanted to know if she was receiving the correct treatment. To be able to explain this diagnosis, let us go back to the very beginning.

Back to the beginning

Diabetes mellitus, a condition where blood glocose is high, has been described for thousands of years. It was initially diagnosed by testing for the sweet (mellitus) taste of urine.

Over time it became clear that not all diabetes is the same and so began attempts to classify the various types. This classification has changed over the years and we now categorise diabetes according to the cause of the diabetes. The four main types are:

  • Type 1

In this type, there is significant destruction of the insulin producing beta cells of the pancreas. This is usually due to an autoimmune process that attacks these cells but may occur without any sign of autoantibodies. The latter variant has a very strong family history and is more common in African and Asian populations.

  • Type 2

This is the most common form of diabetes occurring in 90-95% of cases. Usually there is a background of insulin resistance and then progressive loss in insulin secretion from the beta cells.

  • Type 3

This group has over several major subtypes with over 40 individual causes described. The group includes the maturity onset diabetes of the young (MODY) conditions which are single gene mutations; pancreatic diseases such as cystic fibrosis; endocrine disorders; side effects of drugs, such as HIV treatment or other rare genetic conditions.

  • Type 4

By definition, this is hyperglycaemia (high blood glucose) first detected in the second or third trimester of pregnancy. This type is better known as gestational diabetes.

LADA

As you can see, there is no Type 1.5 diabetes. The more accepted term for this type of diabetes is latent autoimmune diabetes in adults (LADA). LADA is a condition that occurs in adults between the ages of 30-50 years. Like Type 1 diabetes, there is autoimmune damage to the pancreatic beta cells. However, this seems to be at a much slower rate than in the young, typical Type 1 diabetes patient. Hence, the term latent.

Why is LADA called Type 1.5 diabetes?

LADA has features from both Type 1 and Type 2 diabetes, so it seems reasonable to call it Type 1.5. However, the cause of LADA is autoimmune beta cell destruction. So, for that reason it must be considered as a subtype of Type 1 diabetes.

We should always consider a diagnosis of LADA in a normal weight patient who has reasonable glucose control, using lifestyle interventions and/or oral medication only. It would be reasonable to test for LADA in such a patient.

LADA/Type 1.5 diabetes symptoms

Initially, patients may experience non-specific fatigue, decrease in concentration and hunger pangs after eating. More typical symptoms, such as weight loss, thirst and blurred vision, develop gradually over months, sometimes even years. Patients are often of normal weight and usually there is no family history of diabetes. They may have another autoimmune condition, such as thyroiditis, rheumatoid arthritis or coeliac disease. The patient is advised on a healthy lifestyle and usually started on oral medication to control glucose, which seems to help for a period. Ultimately, there will always come a point when insulin needs to be initiated.

Confirmation tests for LADA

The only way LADA can be confirmed is to do specific tests to look for the antibodies causing the damage, specifically the glutamic acid decarboxylase (GAD) antibody. A C-peptide level test can also be done to measure how much insulin the pancreas is still producing.

These are not routinely tested and it can be argued that doing these tests, does not necessarily change management. If the patient is having regular check-ups, including HbA1c measurement and testing glucose regularly at home, any deterioration in the diabetes will be detected. The decision to initiate insulin can then be made timeously.

However, we should consider the advantages of doing the antibody testing and establishing if LADA is present as seen below.

Protecting beta cell function

Some of the oral medications available to treat high blood glucose work by stimulating the beta cells of the pancreas to increase their insulin production.

In LADA, this may have the negative effect of speeding up the deterioration of the beta cell and shortening the latent period: patients would need to start insulin sooner.

Metformin is the best oral diabetic medication to begin with as it has no pancreatic action. Rather, metformin decreases the production of glucose in the liver.

Preserving beta cell function

There is evidence that early insulin treatment may assist the beta cells so that they can continue producing insulin for longer periods. A Japanese study looked at 4000 patients with LADA and found that those treated with early insulin took longer to be fully dependent on insulin compared to those patients on oral medications.

Prevention of ketoacidosis

Ketones are formed by the body when fat is used for fuel. The body does this when there is not enough insulin to move glucose out of the blood stream and into the working cells of the body. Unfortunately, these ketones cause the body to become acidotic which is very dangerous.

Patients with LADA could be made aware that a persistent increase in their blood glucose might be heralding the time to start insulin. In this way, there would be less delay and thus, less chance of developing ketones.

Table 1 – Comparison of Type 1 and Type 2 diabetes

DIABETES ADULT ONSET AUTOIMMUNE DIABETES TYPE 2
Type 1 Latent Autoimmune
Autoantibodies YES YES NO NO
Insulin required at diagnosis YES NO NO VARIABLE

MEET OUR EXPERT


Dr Angela Murphy is a specialist physician working in the field of Diabetes and Endocrinology in Boksburg. She is part of the Netcare Sunward Park Bariatric Centre of Excellence as well as a specialist with the Centre for Diabetes Excellence (CDE) network.