Idiopathic Diabetes   (June 24, 2012)

I love the word "idiopathic." Besides making nice sounds as it rolls off one's tongue (id-dee-oh-PATH-ick), its definition is positively murky: it's used to describe a disorder of obscure or unknown cause. At one world-famous authority, it's stated that the word comes from the Greek:  idios (one's own) + pathos (suffering). Yes, that's definitely Greek to me.

Down to business. I received an e-mail which read:   "I saw [the following] information in a blog, and wondering about it? It is LADA relabeled? Is her doctor right?" The blog stated:

"I have Idiopathic Type 1 diabetes, or Type 1b diabetes. I had never heard of this before the doctor called to give me my test results from last week. I had been wondering and wondering about it since last Friday and finally, during lunch, the doctor called to tell me that I have Type 1b diabetes."

Well, first of all, the American Diabetes Association hasn't updated its nomenclature to include using letters for subtype designations (e.g., describing a form of diabetes as  "type 1A" or "type 1B"). (BTW, I'll go with the majority usage that I find on the ‘net and use capitalized letters when discussing these presumed subtypes, and not put a space between the number and the letter.)

Some websites have taken it upon themselves to generate their own definitions. For instance, one website states with pseudo-authoritative confidence that "Type 1 B diabetes is also referred to as idiopathic diabetes, or diabetes of unknown origin. This form of type 1 diabetes is not autoimmune in nature, and tests for islet cell antibodies will come up negative. People with type 1 B have an insulin deficiency and can experience ketoacidosis (a high blood sugar emergency), but their need for insulin injections typically waxes and wanes over time. Patients of African, Hispanic, or Asian descent are more likely to develop type 1 B diabetes." But that website offers no authorship information whatsoever, and is therefore subject to the usual rule of the Internet: when in doubt, don't trust information on the ‘net.

The "official" descriptions of various varieties of diabetes mellitus as promulgated by the American Diabetes Association are in a position statement titled Diagnosis and Classification of Diabetes Mellitus.

As I mentioned recently, the ADA lists type 1 (previously referred to as insulin-dependent diabetes or juvenile-onset diabetes) and type 2 (non–insulin-dependent diabetes or adult-onset diabetes), and other varieties of diabetes, but none of the others were deemed worthy of having a name that includes "Type-whatever-number-is-next." Nor has the ADA used letters for subtypes (such as "1A" or "1B").

But, importantly, in their discussion of what they call type 1, the ADA has a paragraph as follows:

Idiopathic diabetes

Some forms of type 1 diabetes have no known etiologies. Some of these patients have permanent insulinopenia and are prone to ketoacidosis, but have no evidence of autoimmunity. Although only a minority of patients with type 1 diabetes fall into this category, of those who do, most are of African or Asian ancestry. Individuals with this form of diabetes suffer from episodic ketoacidosis and exhibit varying degrees of insulin deficiency between episodes. This form of diabetes is strongly inherited, lacks immunological evidence for β-cell autoimmunity, and is not HLA associated. An absolute requirement for insulin replacement therapy in affected patients may come and go.

Not exactly the same description as the website I mentioned earlier, but close…

There have been other authors who have come up with their own definitions for "type 1B" diabetes. In 2003, a published letter in Diabetes Care discussed the

High Frequency of Type 1B (Idiopathic) Diabetes in North Indian Children With Recent-Onset Diabetes. (BTW, they studied children in the northern part of the country of India, not in American Natives). Their definition of type 1B diabetes seems to have been that any child who had no islet-cell antibodies (or, in other words, who were antibody-negative) was considered to have type 1B, whereas any child with islet-cell antibodies (or in other words, who were antibody-positive) were considered to have type 1A diabetes. Interestingly, in their review there were no differences in clinical features (such age at onset, duration of symptoms before diagnosis, frequency of ketosis, or BMI) or metabolic profile (plasma glucose, A1C, or fasting plasma C-peptide) for children who they categorized as 1A versus 1B.

Back to the question I was asked, whether "type 1B" diabetes is merely an alternate term for LADA diabetes (Latent Autoimmune Diabetes of Adults). That answer is easy, if one postulates that type 1B could be defined as antibody-negative type 1 diabetes, and one remembers that patients with LADA are usually antibody-positive: type 1B would NOT be synonymous with LADA. (Interestingly, LADA is another term that's not used in the ADA position statement.)

Does it matter that some people with apparent type 1 diabetes are antibody-negative (and hence would be labeled by the ADA as having "idiopathic diabetes", or what some folks are calling "type 1B diabetes")? The letter which I mention above stated that those researchers saw no clinical difference between 1A and 1B children in India. But that observation disagrees with the ADA's comments: the ADA seems to think that idiopathic diabetes patients (antibody-negative type 1 patients) are more likely to be of certain ethnicities (African or Asian), be more strongly inherited, and insulin replacement therapy in affected patients may be intermittent.

So some folks who look for all the world like they have type 1 diabetes have no antibodies, and therefore can be labeled as having a subtype of type 1 diabetes that is called "idiopathic diabetes" (or if you prefer, go ahead and call it "type 1B diabetes"). And some of these folks might have different characteristics, such as their race, their predisposition to gift their offspring with the disorder, and with intermittent insulin replacement perhaps being possible. To me, about all that this seems to indicate is that type 1 diabetes is a heterogeneous group of similar disorders, and not just one single disease – and that's been known for some time.