A variety of causes can manifest as diabetes mellitus. While most patients have Type 1 or Type 2 diabetes, other types occur. Identifying the cause is important for management and prognosis.

Type of Diabetes


Type 1

absolute insulin deficiency following destruction of the beta-cells

Type 2

relative insulin deficiency due to a combination of insulin resistance and impaired insulin secretion


diabetes triggered by pregnancy and often remitting afterwards


genetic or acquired (see below)


Other causes of diabetes or impaired glucose handling due to genetic cause primarily affecting insulin production or action:

(1) genetic defect in beta-cell function

(1a) neuroD1 and chromosome 2 (MODY 6)

(1b) glucokinase and chromosome 7p (MODY 2)

(1c) HNF-1alpha and chromosome 12 (MODY 3)

(1d) insulin promotor factor 1 and chromosome 13 (MODY 4)

(1e) HNF-1beta and chromosome 17 (MODY 5)

(1f) HNF-4alpha and chromosome 20q (MODY 1)

(1g) mitochondrial DNA

(2) genetic defect in insulin action (defect in insulin receptor, etc)

(2a) Type A insulin resistance

(2b) leprechaunism

(2c) lipoatrophic diabetes

(2d) Rabson-Mendenhall syndrome)


Other causes of diabetes or impaired glucose handling due to acquired causes:

(1) disease of the exocrine pancreas

(1a) pancreatitis

(1b) cystic fibrosis

(1c) hemochromatosis

(1d) fibrocalculous pancreatopathy

(1e) pancreatic tumor

(1f) trauma or surgery

(2) drug or chemical-induced

(2a) corticosteroids

(2b) treatment of AIDS

(2c) organ transplantation (tacrolimus, other)

(2d) thiazides

(2e) interferon

(2f) Vacor

(2g) nicotinic acid

(2h) pentamidine

(2i) second-generation anti-psychotic agents

(2j) diazoxide

(2k) Dilantin

(2l) beta-adrenergic agonists

(2m) others

(3) endocrinopathies

(3a) acromegaly

(3b) glucagonoma or somatostatinoma

(3c) hyperthyroidism

(3d) aldosternoma or Cushing's disease

(3e) pheochromocytoma

(4) viral infection-related

(4a) cytomegalovirus (CMV)

(4b) congenital rubella

(5) immunologic disorders

(5a) antibodies to insulin receptor

(5b) stiff man syndrome

(6) hereditary disorder associated diabetes (may include one or more of the above mechanisms)

(6a) Klinefelter's syndrome

(6b) Turner's syndrome

(6c) Friedrich's ataxia

(6d) Wolfram's syndrome

(6e) Prader-Willi syndrome

(6f) Down's syndrome

(6g) myotonic dystrophy

(6h) Lawrence-Moon-Bardet-Biedl syndrome

(6i) congenital porphyria

(6j) others


Some patients have a syndrome that shares features of both Type 1 and Type 2 diabetes ("not quite Type 1, not quite Type 2").



Type 1

Type 2

Not Quite


very low









not prone



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