Type 1 diabetes has two subtypes: type 1A includes the common, immune-mediated forms of the disease, and type 1B includes the non-immune forms. The common form of type 1A diabetes is probably caused by multiple actions, and interactions, of genetic and environmental factors. Genetic linkage studies have shown significant associations between the HLA region on chromosome 6p21 and type 1A diabetes. In addition, class II genes encoding HLA-DR and HLA-DQ, as well as some other HLA foci, seem to account for most of the genetic risk for type 1A diabetes. Thus, children who carry both of the highest risk HLA haplotypes (DR3-DQ2 and DR4-DQ8) have a risk of approximately 1 in 20 for developing type 1 diabetes by the age of 15 years. Current approaches for the prediction of type 1 diabetes rely on the major genetic risk factors, genotyping for HLA-DR and HLA-DQ loci, and screening for autoantibodies directed against islet cell antigens (Figure 28.6).
Twice-daily injections of short- and intermediate-acting insulins are most common in paediatric practice. Monomeric insulins, such as lispro or aspart, which can be injected with or even after meals, are helpful in toddlers with their erratic appetites. These insulin analogues may also reduce nocturnal hypoglycemia. After the diagnosis of diabetes, there is sometimes a partial remission (the ‘honeymoon period’), lasting from a few months to 2 years, during which the insulin dose is <0.5 U/kg. This is due to a transient improvement in residual beta-cell function. It is usual to maintain low-dose insulin treatment during the honeymoon period. Use of multiple daily injections, or long-acting analogues, has no effect on the duration of this honeymoon phase. Children and young adults with type 1 diabetes should be screened regularly for complications (Box 28.1).
Hypoglycemia is common in children with diabetes, particularly in younger children who cannot communicate and in whom signs of hypoglycemia (pallor, drowsiness, lethargy) are often detected by the parents (Figure 28.7, Table 28.2). Moreover, young children are at risk of later neuropsychological impairment from severe, recurrent hypoglycemia. Presumably, this relates to the effect of hypoglycemia on the developing brain. Even older children are less able to detect hypoglycemia than adults. Behavioral manifestations of hypoglycemia include aggression, irritability, sadness, fatigue and naughtiness.
Continuous subcutaneous insulin infusion (CSII, insulin pump therapy) is an alternative option for achieving strict metabolic control in selected patients, particularly in children who have been unable to maintain adequate glycemic control with multiple-dose injections without frequent, unpredictable and disabling hypoglycemia (Figure 28.8). Experience of CSII in children is less extensive than in adults but it is rapidly gaining in popularity. As with adults, careful selection of patients and a healthcare team experienced in insulin pump therapy are essential.
The prevalence of impaired glucose tolerance and type 2 diabetes in children is increasing in parallel with the increase in childhood obesity. When type 2 diabetes is diagnosed in young people, most are undergoing puberty, so perhaps the increased insulin resistance of puberty triggers or unmasks the type 2 diabetes. Most of these children also belong to a high-risk ethnic group, i.e. African, Caribbean, Asian or Latino descent. There may be clinical signs of insulin resistance apart from obesity, such as acanthosis nigricans or the polycystic ovary syndrome. The pathophysiology of type 2 diabetes in childhood is probably similar to that in adults (see Chapter 7).
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Rudy Bilous MD, FRCP, Professor of Clinical Medicine, Newcastle University, Honorary Consultant Endocrinologist, South Tees Foundation Trust, Middlesbrough, UK
Richard Donnelly MD, PHD, FRCP, FRACP, Head, School of Graduate Entry Medicine and Health, University of Nottingham, Honorary Consultant Physician, Derby Hospitals NHS Foundation Trust, Derby, UK
A John Wiley & Sons, Ltd., Publication This edition first published 2010, © 2010 by Rudy Bilous and Richard Donnelly. Previous editions: 1992, 1999, 2004
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