PEDIATRICS Vol. 111 No. 4 April 2003, pp. 860-863
Clinical, Autoimmune, and HLA Characteristics of Children Diagnosed With Type 1 Diabetes Before 5 Years of Age
From the Pediatric Diabetes Center and Transplant Immunology Center, Loma Linda University Children’s Hospital, Loma Linda, California
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Background. Little is known about auxologic, autoimmune, and HLA characteristics specific to children with early-onset diabetes (EOD). HLA subtypes have been shown to play an important part in the determination of islet-cell autoimmunity and in the pace and intensity of the ß-cell destructive process.
Objectives. Our goals were to: 1) outline auxologic, autoimmune, and HLA class II characteristics of children diagnosed with type 1 diabetes before 5 years of age (EOD); 2) evaluate differences between EOD and later-onset or non-age-stratified type 1 diabetes; and 3) investigate the relation between type 1 diabetes-related HLA subtypes and markers of diabetic autoimmunity in EOD.
Methods. Forty children with EOD were studied. Auxologic and antibody radioimmunoassay data were obtained by retrospective analysis of records. HLA diabetes-related class II alleles were typed by polymerase chain reaction using sequence-specific primers.
Results. At diagnosis, the average age of the EOD study patients was 2.6 years, body mass index was 16.9 kg/m2, and weight was 106% of average weight for height. When compared with a matched subgroup of children with later-onset type 1 diabetes, preschoolers did not significantly differ in terms of birth weight or body mass index. The frequency of positive islet cell antibodies 512 and glutamic acid decarboxylase 65 antibodies was significantly less in EOD (28.6% and 31.6%, respectively). There were significant differences in the frequencies of some diabetes-related HLA alleles and haplotypes between the early-onset group and a large non-age-stratified type 1 diabetes group. None of the patients with EOD had either of the protective DRB1*1501 or DQB1*0602 alleles. There was a negative correlation between glutamic acid decarboxylase and the predisposing haplotype DR3/DQ2.
Conclusions. Children diagnosed with type 1 diabetes before 5 years of age may have different diabetes-related autoimmune and genetic characteristics from those diagnosed at a later age.
Key Words: early-onset diabetes • autoimmune markers • human leukocyte antigen subtypes
Abbreviations: EOD, early-onset diabetes • HLA, human leukocyte antigen • ICA, islet cell antibodies • GAD, glutamic acid decarboxylase • IAA, insulin auto antibody
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INTRODUCTION |
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The highest increase of incidence in type 1 diabetes over the past decade occurred in children under 5 years of age, a group at particular risk for diabetes-related natural and iatrogenic morbidity.1 Little is known about the genetic background and the clinical and autoimmune status of children with type 1 diabetes presenting before 5 years of age.2 Such early-onset of type 1 diabetes suggests a high risk for development of long-term diabetic complications.3 Recent data showed more severe metabolic decompensation and poorer ß-cell residual function at clinical onset of type 1 diabetes in very young children.4 Differences in genetic susceptibility for type 1 diabetes have been observed with early-onset of the disease.5 Moreover, neonates, infants, and toddlers with type 1 diabetes are more likely to have a father with type 1 diabetes than diabetic children diagnosed at a later age.6 Environmental triggers in infancy and early childhood may accelerate the onset of diabetes. For example, enteroviral infection documented by polymerase chain reaction was detected in twins developing type 1 diabetes in infancy, before detection of islet-cell antibodies.7 Differences in exposure to environmental air pollutants in early-onset diabetes (EOD) have just begun to be investigated. Humoral markers of diabetic autoimmunity have been used to characterize and identify risk for type 1 diabetes regardless of age of onset.8 HLA class II genes have been linked to predisposition to and protection from type 1 diabetes at any age.9 This study focuses on diabetes-related clinical, autoimmune, and genetic (HLA class II) characteristics in children diagnosed before 5 years of age.
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METHODS |
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We performed retrospective analysis of a convenience sample of all 40 patients diagnosed with type 1 diabetes before 5 years of age at the pediatric diabetes center of Loma Linda University Children’s Hospital, from 1995 to 2000. Diagnosis of type 1 diabetes was based on clinical and biochemical evidence of insulin-deficient hyperglycemia. A randomly selected sample of equal size with later-onset diabetes diagnosed at the same center over the same period was used for comparison of clinical and autoimmune variables. The national disease research interchange human biological database (HBDI, Philadelphia, PA) of 671 nonstratified subjects with type 1 diabetes10 was used to conduct HLA comparisons. Diabetes and thyroid-related antibodies were measured by a commercial radioimmunoassay (Endocrine Sciences, Calabassus, CA). HLA class II subtyping was done at Loma Linda University Transplant Immunology Center using sequence-specific oligonucleotide probes. Reagents for amplification and probing were obtained from Lifecodes Corporation (Stamford, CT).
2 and Fisher’s exact tests were used for analysis of categorical variables, and 2-tailed t test was used for continuous variables. The protocol was reviewed and approved by Loma Linda University Institutional Review Board, and appropriate signed consent and assent forms were obtained. |
RESULTS |
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The average ages of the early and later-onset type 1 diabetes groups were 2.6 and 9.9 years, respectively (Table 1). Older children had a higher body mass index, but neither group was overweight in absolute or relative terms. Gender distribution of the 2 groups was similar with a slight preponderance of females. Ethnic breakdown was not significantly different between the 2 groups and was also representative of the background population for their respective geographic area. Winter was the predominant season for diagnosis of type 1 diabetes, and season-based frequencies of diagnosis were not significantly different between the 2 age groups.
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The frequency of having a honeymoon period after diagnosis was strikingly, but not significantly, decreased in the early-onset group (Table 2). At initial presentation, there was a higher frequency of symptoms suggestive of a concomitant viral illness, and a higher frequency of ketoacidosis in the early-onset group, although the duration of stay in the intensive care unit was also influenced by different physicians’ preferences.
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Autoimmune marker studies done within 1 month of diagnosis showed no significant difference in the frequencies of positive thyroid peroxidase antibody and thyroglobulin antibodies based on diabetes age of onset. The frequencies of glutamic acid decarboxylase (GAD) and islet cell antibodies (ICA)512 were significantly lower in the early onset group (Table 3). No significant differences were observed for insulin auto antibodies (IAAs), which were drawn at variable time points after the institution of insulin therapy. In contrast with a 20% incidence for hypothyroidism in the later-onset group, none of the patients with EOD and positive thyroid antibody(s) have evidence of thyroid dysfunction to date.
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Genotype analysis of the group with EOD focused on HLA class II genotypes, the most studied of the type 1 diabetes candidate genes. More than 50 single and combination alleles spanning the loci DQA1 (0101–0606), DQB1 (0201–0617), and DRB1 (0101–1602) were tested. These included predisposing alleles DR3 and DR4, protective alleles including DQB1 0602, as well as predisposing and protective haplotypes (allele combinations): DR3/DQ2 and DR4/DQ8 versus DR15/DQ6. Frequencies compared with HBDI nonstratified database of 671 subjects with type 1 diabetes showed the following statistically significant observations in the early-onset group: 1) a lower frequency of DR4 0401 (15% vs 47%, P < .01); 2) a higher frequency of DRB1 0407 (13% vs .3%, P < .01); 3) a higher frequency of DQB1 0303 (8% vs 1%, P = .03); 4) a lower frequency of the predisposing haplotype DRB1 0401/DQ8 (13% vs 39%, P < .01); 5) a higher frequency of DRB1 0405/DR3 (13% vs 3%, P < .01); 6) absence of the protective alleles DQB1 0602 and DRB1 1501 in all early-onset disease patients. Moreover, there was a negative correlation between GAD antibody and the predisposing haplotype DR3/DQ2. Ethnic trends in EOD were most pronounced in the DR locus (Table 4). DR4 0401 was present in 35% of white EOD patients but absent in all Hispanic patients. DR4 0401/DQ8 was present in 71% of white patients but absent in all Hispanic patients. DR4 0402/DQ8 was absent in all white but present in 93% of Hispanic patients. DR4 05 was absent in all white but present in 21% of Hispanic EOD patients.
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Because the focus of the study was EOD, and because of funding limitations, HLA testing of our later-onset patient subgroup was not performed.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Despite the small number of study children with onset of diabetes before 5 years of age, clinical and autoimmune differences between them and children with later-onset disease have been suggested by previous studies.11 The higher frequency of ketoacidosis in younger children at diagnosis may partly reflect age-related delay in verbalization and toilet training, which can mask diabetes symptoms. Older children have free access to fluids, thus self-medication, as opposed to early-onset younger children who are usually dependent on guardians. Therefore, timing of diagnosis may have little relevance to timing of onset of disease. The higher frequency of symptoms of concomitant illness at presentation was neither confirmed by studies of viral titers nor compared with frequencies in nondiabetic children of similar age. However, the clinical data, including a trend for lack of a honeymoon period, suggest a more rapid and/or severe ß-cell destructive process in younger children.
Earlier reports on diabetes autoimmune markers showed that young children are usually positive for 1 or more markers at the time of diagnosis,12–14 and that there is a correlation between titer levels and the rate and intensity of ß-cell destruction.4 This implies that early-onset of type 1 diabetes should be associated with higher diabetes antibody titers. Other data, including ours, provide evidence to the contrary. GAD and ICA512 antibody results suggest a relative lack of a diabetes-specific humoral immune response in infants and toddlers with new-onset diabetes. The finding may reflect age-related differences in type 1 diabetes autoimmunity or the existence of nonautoimmune diabetogenic mechanisms in younger children. The latter possibility is strengthened by the observation of a higher frequency of symptoms of a viral illness at diagnosis in the very young.
The incidence of type 1 diabetes is disproportionately increasing in infants and toddlers.15,16 This group of children was generally excluded from the recent US-based Diabetes Prevention Trial, which uses ICA positivity as the first line of screening for diabetes risk.17 Our preliminary data, albeit in a small number of patients, and that of others4 suggest that diabetes in the very young should be viewed as a separate entity for purposes of early detection or prevention of type 1 diabetes. More thorough and large-scale studies are needed to identify specific predisposing factors for EOD. Identification of such factors may facilitate the design of antigen-specific immune intervention trials for infants and toddlers at risk for type 1 diabetes.
The significantly lower frequencies of diabetes ICA and GAD antibodies at diagnosis in our study can be a result of a rapid environmentally triggered ß-cell destructive process. These antibodies may be late-appearing if their titers are followed longitudinally. Markers of cellular autoimmunity might have been detected if tested for.18 Alternatively, a direct toxic ß-cell effect may be the predisposing mechanism in a subgroup of children with EOD. Results of IAA drawn at various time points following institution of insulin therapy cannot be interpreted with certainty.19
HLA findings in this pilot study of EOD have not to our knowledge been previously described or published. The unique differences in frequencies of predisposing and protective alleles and/or haplotypes in early-onset disease may in part reflect the genetic diversity of this group compared with others previously tested. Race/ethnicity-based diabetes-related HLA data were not available as a reference tool. Results highlight caveats that may hinder identification of diabetes risk in children of diverse ethnic backgrounds, thus affecting their participation in current type 1 diabetes prevention trials.20 The wide spectrum of candidate diabetogenes,21 within and outside the HLA locus, further adds to the complexity of diabetes risk identification in young children. The study points to another potential caveat of type 1 diabetes prevention trials: a possible negative correlation between genetic and autoimmune risks as screened for by current strategies.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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The above pilot study suggests that onset of type 1 diabetes before 5 years of age is associated with increased illness and diabetic ketoacidosis at presentation, low frequency of ICA and GAD antibodies, and lower-than-expected frequency of known diabetogenes. Furthermore, diabetes-related HLA class II frequencies in children with EOD have ethnic-related distribution tendencies. The study raises the possibility that preschool diabetes may not be classic type 1A disease, and may thus require unique prevention and therapeutic strategies.
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ACKNOWLEDGMENTS |
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This work was funded in part by a research grant from the Department of Pediatrics at Loma Linda University.
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FOOTNOTES |
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Received for publication Sep 18, 2002; Accepted Dec 4, 2002.
Address correspondence to Eba H. Hathout, MD, FAAP, Chief, Division of Endocrinology, Director, Pediatric Diabetes Center, Loma Linda University Children’s Hospital, 11175 Campus Street, CP A1120R, Loma Linda, CA 92354. Email: ehathout{at}ahs.llumc.edu
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PEDIATRICS (ISSN 1098-4275). ©2003 by the American Academy of Pediatrics
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