Secondary diabetes means to know the primary cause

Author: Dr Sorin Ioacara | Last update: November 9th, 2020

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Discover here: Definition | Secondary diabetes classification | Monogenic diabetes

About 5% of all diabetes cases are secondary. Unfortunately, doctors fail to recognize them in medical practice. As a result, almost all of these cases are diagnosed as type 1 or type 2 diabetes. For example, Maternal Inherited Diabetes and Deafness (MIDD) diabetes can affect up to 1% of patients with diabetes, but it is often undiagnosed.

We will start with the definition of secondary diabetes and its classification. Next, we will discuss more broadly about monogenic diabetes and its subtypes, i.e. neonatal diabetes.


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Secondary diabetes is a heterogeneous group of disorders, which share the fact that doctors know the primary cause. A synonym sometimes used is “other specific types of diabetes”. The reality is that, in the classical forms of diabetes, we don’t know the primary source of the disease. For example, if we would have known the real cause in a patient with type 1 diabetes, then it wouldn’t be called “type 1”. The disease name would automatically become diabetes secondary to that cause.

Centres of excellence in diabetes manage to identify more and more cases of secondary diabetes. The ultimate goal is for the diagnosis of type 1 or type 2 diabetes to become as rare as possible. In other words, diabetes of unknown cause as a diagnosis will hopefully become the exception, not the rule, as it is now.

Classification of secondary diabetes

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There are currently over 100 causes of secondary diabetes. Each of them is responsible for a form of secondary diabetes. Knowing the cause gives the possibility of a personalized treatment. Often, the initial treatment received by the patient will be significantly changed. The metabolic control obtained with the right treatment is definitively better to the one previously received by the patient.

The main categories of secondary diabetes are the following:

  1. Monogenic diabetes affecting insulin secretion
  2. Genetic defects in insulin action
  3. Diseases of the exocrine pancreas
  4. Endocrine diseases
  5. Medicines and toxic substances
  6. Infections
  7. Rare forms of autoimmune diabetes
  8. Complex genetic syndromes

Monogenic diabetes affecting insulin secretion

Many chromosomes flying suggesting monogenic diabetes

The term “monogenic” means affecting only one gene. However, that gene can be “broken” in one or more places. To summarize, monogenic diabetes results from one or more defects in a single gene. As a result, insulin is either secreted inappropriately or no longer works as it should. In this section, we cover monogenic diabetes with reduced insulin secretion. The primary forms of diabetes addressed here are neonatal diabetes and MODY (Maturity Onset Diabetes of the Young).

Neonatal diabetes

Neonatal diabetes mellitus has a dedicated chapter. Neonatal diabetes appears relatively quickly after birth. Increased blood sugar levels sometimes appear from 1-2 weeks of life. In the vast majority of cases, severe symptoms and hyperglycemia occurs before six months of life. Unfortunately, the clinical diagnosis is often with diabetic ketoacidosis.


  1. American Diabetes Association Guideline 2020
  2. ISPAD Clinical Practice Consensus Guidelines 2018
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