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INTRODUCTION

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ESSENTIALS OF DIAGNOSIS & TYPICAL FEATURES

  • Polyuria, polydipsia, and weight loss.

  • Hyperglycemia and glucosuria often with ketonemia/ketonuria.

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GENERAL CONSIDERATIONS

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Type 1 diabetes (T1D) is the most common type of diabetes mellitus in people younger than 20 years, but can develop at any age and most cases are diagnosed after age 20. The classical presentation includes increased thirst (polydipsia), urination (polyuria), and weight loss; however, the patient may be overweight or even obese. T1D is further divided into T1a (autoimmune) (~95% of the cases) and T1b (idiopathic) diabetes. T1a diabetes is marked by presence of autoantibodies to islet cell autoantigens (insulin, GAD65, IA-2, and ZnT8) and high-risk HLA (human leucocyte antigen) haplotypes (DR4, DQ8, and DR3/DQ2). Insulin production, measured by fasting or stimulated C-peptide levels, is usually low. In the United States, T1D affects an estimated 1.5 million people, including 160,000–200,000 patients younger than age 20 (~25,000 diagnosed annually).

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Type 2 diabetes (T2D) is a heterogeneous phenotype diagnosed most often in persons older than age 40 who are usually obese and initially not insulin-dependent. T2D is rare before age 10, but has increased in frequency in older children as a consequence of the epidemic of obesity. The vast majority of the 26 million patients with diabetes in the United States have T2D, but only approximately 16,000 patients are younger than age 20 (~5000 diagnosed annually).

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Monogenic forms of diabetes can be diagnosed at any age. They account for less than 1% of childhood diabetes, but form the majority of cases diagnosed before the ninth month of life. Neonatal diabetes is transient in about half of the cases; if persistent, it presents a significant clinical challenge. Some infants respond better to sulfonylurea than insulin. Maturity-onset diabetes of the young (MODY) presents as a nonketotic and usually non–insulin-dependent diabetes in the absence of obesity or islet autoantibodies. A strong family history of early-onset diabetes is common. The most frequent forms are due to mutations in glucokinase or hepatic nuclear factor 1 or 2 genes. Glucokinase mutations rarely require therapy; other forms respond to oral hypoglycemic agents or insulin. Commercial and research-oriented genotyping services are available to aid correct diagnosis.

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Pathogenesis

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A. Type 1 Diabetes
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Type 1 diabetes results from autoimmune destruction of the insulin-producing β cells of the pancreatic islets. This destruction occurs over months or years and symptoms do not appear until most of the pancreatic islets have been destroyed.

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The incidence is the highest in children of European ancestry, followed by African Americans and Hispanics; the rates are low in Asians and Native Americans.

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About 6% of siblings or offspring of persons with T1D also develop diabetes (compared with prevalence in the general population of 0.2%–0.3%). However, fewer than 10% of children newly diagnosed with T1D have a parent or sibling with the ...

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