We may also be aware of some minor types like LADA (latent autoimmune diabetes of adults), a slower-onset form of autoimmune diabetes that appears in adults. Another type is MODY (maturity-onset diabetes of the young), which often, but not always, appears in children or young people. It is monogenic, meaning a mutation in only one gene causes the disease, and the affected gene is dominant, meaning that you can inherit only one copy of the gene from one parent and a normal gene from the other parent and you'll get MODY.
Type 2 diabetes is polygenic, meaning a lot of genes are usually involved.
Other forms of diabetes include gestational diabetes, a usually temporary form of diabetes that occurs in late pregnancy and then goes away after the baby is born, although having gestational diabetes greatly increases your risk of getting type 2 diabetes later. And there are various rare forms of diabetes as well as diabetes induced by taking drugs, including steroids.
But there's another form of diabetes that seems to becoming more and more common, especially in Africa, and that's Flatbush diabetes, named after the New York area where it was described some years ago.
It's also been called a lot of other things, including atypical diabetes, type 1B diabetes, idiopathic [meaning the cause is unknown) type 1 diabetes, and ketosis-prone type 2 diabetes.
I'll use the term Flatbush diabetes because I find it easier to rememember colorful nicknames, and also because it doesn't require one to decide if this form of diabetes is really type 1 or type 2. In fact, it seems to be somewhat in between.
Flatbush diabetes is found primarily in nonwhite populations, especially those of sub-Saharan African descent, although Asians, Hispanics, and even Caucasians can be diagnosed with it.
The hallmark of Flatbush diabetes is presenting with sudden onset of extremely high BG levels (BG levels of 700 mg/dL and A1c's of 12 to 14 are not uncommon), in diabetic ketoacidosis, or DKA. Because DKA used to be considered a hallmark of type 1 diabetes (in older terminology, type 2 diabetes was sometimes called ketosis-resistant diabetes), patients with Flatbush diabetes were originally considered to be type 1, and hence the name atypical type 1 or type 1B (regular type 1 diabetes is classified as type 1A according to the current official classification system).
However, patients with Flatbush diabetes don't have antibodies against beta cells; unlike "regular" type 1 diabetes, it's not an autoimmune disease. This is what it was sometimes called idiopathic type 1 diabetes.
Patients with Flatbush diabetes are also often overweight, as in type 2 diabetes, and have relatives with type 2 diabetes, and they may have some insulin resistance, which is one reason some people use the term type 1.5 diabetes. I think that term type 1.5 should be avoided, because it's sometimes used for LADA and sometimes used for type 1 patients who also show signs of insulin resistance.
A major distinguishing feature of Flatbush diabetes is that when the very high BG levels on diagnosis are brought down with insulin, the patients can often do quite well with oral drugs, or even just diet and exercise, for months or even years. Patients with "regular" type 1 diabetes often have a "honeymoon period" in which their insulin requirements are fairly low, but they always progress toward insulin dependence, and if they stop taking insulin they go into DKA.
Some patients with Flatbush diabetes do relapse and have another episode of DKA. But this relapse is often preceded by gradually increasing high BG levels. Others never relapse into DKA. After 10 years, about 60% do need insulin for good control, but this is close to the percentage of people with type 2 diabetes who use insulin after 10 years with the disease.
Flatbush diabetes is becoming more and more common in Africa, and in America, it now accounts for up to 50% of the cases among African Americans who are first diagnosed with DKA. No one is sure exactly what causes it, but it has been suggested that these patients are extremely sensitive to temporary damage to the beta cells by glucotoxicity and lipotoxicity, and when those conditions are reversed with insulin and diet, the beta cells are able to recover.
There may turn out to be several subtypes of Flatbush diabetes. Some patients are not able to control without insulin after their diagnosis whereas most are.
Recently, some people have suggested that Flatbush diabetes may be precipitated by a viral infection, for example, herpes infection. Why this causes this particular form of diabetes in some people and not others is not yet known.
So what does all this mean for you? Most of us don't really care how the official groups choose to name our form of diabetes. Whether Flatbush diabetes is type 1 or type 2 depends on how you define type 1 diabetes.
If you define type 1 as having antibodies against beta cells, then it would be type 2. If you define type 1 as being prone to DKA, then it would be type 1. If you define type 2 as having insulin resistance, then it would be type 2.
But who cares what they call it. If you're of nonwhite ethnic background and you were diagnosed with very high BG levels in ketoacidosis and told that you had type 1 diabetes, you might want to see your doctor to discuss whether or not you're likely to have Flatbush diabetes.
If you've never been tested for antibodies, the results of such a test would give a clue. If you have the antibodies, you're probably "regular" type 1 diabetes, and you'll have to stay on insulin. If you don't have the antibodies, there's a chance you could do well on just oral drugs.
Among those diagnosed with Flatbush diabetes, some are nevertheless insulin dependent and others are not. There's a lot we don't yet know about this disease. But the more we're all aware that it exists, the more our physicians will be apt to spot patients who have it. And the more patients are correctly diagnosed, the better their treatment will be.