Idiopathic type 1 diabetes, by definition, has no known etiology. Although only a minority of type 1 diabetic patients fall into this category, it is reported that the majority are of African or Asian descent. Individuals with this form of diabetes are considered to present heterogeneous clinical manifestations (1). Imagawa et al. (2) reported a new subtype of type 1 diabetes characterized by fulminant onset, absolute insulin deficiency, and absence of β-cell autoimmunity in Japanese adults. We reported similar cases of idiopathic type 1 diabetes in Japanese children.
Among 85 Japanese children with type 1 diabetes, 14 (16.5%) were classified as having idiopathic type 1 diabetes with no evidence of anti-islet autoantibodies. Of these 14 patients, 6 had a subtype of markedly abrupt onset. They consisted of five girls and one boy, aged 1.9–15.1 years at onset. Five of the six children had suffered viral infections before the onset of disease: two with Coxsackie virus B, one with influenza virus, one with mumps virus, and one with virus of unknown origin. The duration of hyperglycemic symptoms before the onset of overt diabetes was <18 days (range 5–18) in all six patients. Three patients had a particularly shorter symptomatic period of <7 days. Although all the patients showed high plasma glucose levels (565–772 mg/dl), all but one had HbA1c values <8.0% (6.6–7.6) at diagnosis. This suggests that the short symptomatic period before the onset of overt diabetes might be reflected by a low HbA1c value. All had ketoacidosis with bicarbonate levels <18 mmol/l (13–18) at onset. Four patients experienced impaired consciousness. They exhibited low or undetectable values (0.3–0.4 ng/ml) of serum C-peptide. This implies that β-cells were completely destroyed from the time of onset. One patient had first-degree relatives with type 2 diabetes, while none had family members with type 1 diabetes. All the patients had high-risk HLA typing (either HLA-DR4 or -DR9) for type 1 diabetes.
From these findings, the rapid onset form of idiopathic type 1 diabetes may not be rare in the Japanese population. This form is characterized by markedly abrupt onset with a severe metabolic disorder and absolute deficiency of insulin secretion at onset. Viral infection may be associated with the rapid destruction of β-cells. Ethnic and environmental factors may play a role in the etiology and clinical heterogeneity of idiopathic type 1 diabetes.
Address correspondence to Tatsuhiko Urakami, MD, Department of Pediatrics, Nihon University School of Medicine, 1-8-13 Kandasurugadai, Chiyoda-ku, Tokyo, 101-8309 Japan. E-mail: firstname.lastname@example.org.