This is the second national surveillance study to report on the incidence of type 2 diabetes in children and the first to report the incidence and clinical features at presentation of type 2 diabetes and other forms of non–type 1 diabetes in Canadian children. Based on provincial database registries (13
) and historical evidence (10
), the incidence of type 2 diabetes in children in Canada seems to be increasing. Obesity seems to be the single most important risk factor for type 2 diabetes, a finding common to other studies (2
). Interestingly, 8% of children with type 2 diabetes in our study were <10 years of age at presentation. In the U.S. SEARCH for Diabetes in Youth Study, only 3.6% of cases of type 2 diabetes occurred in children <10 years of age (3
), indicating that this may be a finding unique to the Canadian population. Our results highlight the fact that pediatric type 2 diabetes is not exclusive to the adolescent age-group and can occur in younger children. Similar to other studies (18
), treatment varied considerably, highlighting a need for clinical trials to identify optimal treatment strategies for pediatric type 2 diabetes.
The overall observed minimum incidence of type 2 diabetes in Canadian children is three times the rate reported in the U.K. (2
) and approximately one-quarter of that of the U.S. for children >10 years of age (3
). Although the observed minimum incidence of type 2 diabetes in Canadian Caucasian and Asian children is comparable to that reported by the U.K., the incidence in African/Caribbean children is twice that of the U.K. (2
). Canadian and U.K. incidence estimates are easily comparable because of similar surveillance methodologies. The SEARCH study included 10 locations that were considered representative of the multiethnic distribution of the U.S. population. Differences in U.S. and Canadian estimates may relate to variations in ethnic distribution and screening practices or a sampling bias toward sites with higher proportions of ethnic groups at higher risk for type 2 diabetes in the SEARCH study. To our knowledge, ours is the first population-based study to report the national incidence of medication-induced and monogenic diabetes.
Canadian Aboriginal children <18 years of age have the highest incidence of type 2 diabetes and the majority of these children are from Manitoba, explaining the 20-fold higher incidence rate of type 2 diabetes in this province. This finding is comparable to the U.S., which reports an incidence of type 2 diabetes in American Navajo youth aged 10–14 years of 22.4 cases per 100,000 person-years and 39.34 cases per 100,000 person-years in those aged 15–19 years (19
). Interestingly, type 2 diabetes in American Indian children <10 years of age is rare (19
); however, in Canadian Aboriginal children, 11 cases (11%) of type 2 diabetes occurred in children <10 years of age. This finding suggests that clinical practice guidelines on childhood type 2 diabetes may require revision for selected populations (20
). Finally, although Aboriginal children are at the highest risk for type 2 diabetes, 50% of clinically diagnosed type 2 diabetes occurred in non-Aboriginal children.
The presence of hyperglycemia, ketosis, and pancreatic autoimmunity typically suggests a diagnosis of type 1 diabetes. In this study, 44% of children with type 2 diabetes presented with ketonuria, 10% presented in DKA, and a small percentage exhibited the presence of GAD and insulin antibodies. These findings are similar to those reported in the literature (2
). The SEARCH study reported that 21.2% of children with clinically diagnosed type 2 diabetes were positive for GAD antibodies (3
). There is debate as to whether these youth have been misclassified as having type 2 diabetes; however, clinically they present with “typical” features of type 2 diabetes including obesity and acanthosis nigricans. Furthermore, they respond quickly to insulin treatment and can wean off insulin for extended periods of time (23
). Therefore, the presence of ketonuria and/or pancreatic autoimmunity does not preclude type 2 diabetes in the pediatric age-group. Additional studies are necessary to better understand the relationship of pancreatic autoimmunity to the etiology and natural history of diabetes in children.
This study was limited by factors common to other population-based surveillance studies. Our study generated a minimum incidence rate of pediatric non–type 1 diabetes for the following reasons: 1
) children with diabetes seen by nonparticipating physicians and nonresponders were not captured; 2
) classification was not possible when case reports were incomplete; and 3
) reporting physicians may not have recognized all children with cases of non–type 1 diabetes. The incidence of type 2 diabetes in Saskatchewan seems to be low. This may reflect the unique Aboriginal groups and other ethnic groups that live in that region of the country. The possibility of low reporting rates by pediatricians and family doctors in that province remains. The population estimate for Saskatchewan (233,900) represents only 3% of the total Canadian population of children <18 years of age, and, therefore, this underestimation probably had minimal impact on Canadian incidence rates. A previous surveillance study using the CPSP methodology reported cases from 7 of 13 provinces and territories, which represented 92% of the Canadian population (24
). Second, our study depended on physician-based classification of diabetes followed by review and classification by clinician investigators. This methodology was similar to that used in the U.K. where, 1 year after their initial study, only one case of type 2 diabetes was reclassified (18
). In the SEARCH study, differentiation of type 1 and type 2 diabetes was based on the diagnosis made by reporting physicians without review of clinical data by study investigators. Third, obesity-related morbidities such as hypertension and dyslipidemia were considered to be present if the reporting physician indicated as such; clinical or laboratory evidence was not requested. Last, testing for monogenic diabetes is not widely available in Canada. Patients with a typical family history and natural history of disease were classified as having monogenic diabetes even without confirmed genetic testing. Therefore, the calculated incidence of monogenic diabetes may be either an over- or underestimate of the true incidence.
Assessment of the completeness of ascertainment (i.e., capture-recapture method) using independent sources of information (i.e., prescription data and hospitalization) was not possible because many children with type 2 diabetes are not receiving medication and hospitalization is rare. It is likely that most new cases of non–type 1 diabetes in children were detected, as almost all Canadian children with uncommon conditions are referred to pediatric practitioners. In this study, 92% of cases were reported by pediatricians or pediatric endocrinologists, reflecting the model of care for pediatric chronic disease in Canada. In addition, a type 2 diabetes registry in Manitoba reports 35–45 new pediatric cases per year (25
), a number that is consistent with our study results: a total of 69 new cases of type 2 diabetes were reported in Manitoba over 2 years. In the present study, >75% of children with type 2 diabetes were reported by a pediatric endocrinologist. Every region in Canada is served by a team specializing in the care, education, and support of children with diabetes. A particular strength of this study is that surveillance occurred over a 24-month period and reporting rates remained consistent over this time period.
A sensitivity analysis was conducted to account for the small enriched sample of family physicians who participated in this study. Pediatricians were excluded from the sensitivity analysis because participation rates were high, the sample was not enriched, and previous CPSP surveillance studies with similar participation rates did not require a sensitivity analysis (24
). The maximum and conservative incidence rates were calculated to provide confidence intervals between which the true incidence of non–type 1 diabetes lies. Last, our response rates of 79–95% were acceptable for this type of surveillance study; however, cases could have been missed because of lack of reporting.
This prospective national surveillance study for non–type 1 diabetes provides information on the existing spectrum of non–type 1 diabetes in Canadian children. Until now, the majority of epidemiological data on pediatric type 2 diabetes originated from Manitoba where virtually all cases occur in Aboriginal youth. The results of this study provide a more accurate representation of type 2 diabetes in Canadian children and provide baseline incidence data based on Canada's unique ethnic, cultural, and geographic characteristics. As rates of type 2 diabetes increase, surveillance information is critical to inform health policy makers, track success of prevention and treatment strategies, and increase awareness among health care providers.