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. 2008 Aug;31(8):1546-9.
doi: 10.2337/dc08-0239. Epub 2008 May 16.

The rising incidence of type 1 diabetes is accounted for by cases with lower-risk human leukocyte antigen genotypes

Spiros Fourlanos  1 , Michael D Varney, Brian D Tait, Grant Morahan, Margo C Honeyman, Peter G Colman, Leonard C Harrison
Affiliations
Free PMC article

The rising incidence of type 1 diabetes is accounted for by cases with lower-risk human leukocyte antigen genotypes

Spiros Fourlanos et al. Diabetes Care. 2008 Aug.
Free PMC article

Abstract

Objective: The rising incidence of type 1 diabetes has been attributed to environment, implying a lesser role for genetic susceptibility. However, the rise could be accounted for by either more cases with classic high-risk genes or by cases with other risk genes. Separately, for any degree of genetic susceptibility, age at presentation may decrease in a permissive environment. To examine these possibilities, human leukocyte antigen (HLA) class II DRB1 genes known to confer risk for type 1 diabetes were analyzed in relation to year of birth and age at diagnosis over the last five decades.

Research design and methods: Caucasoid subjects (n = 462) diagnosed with type 1 diabetes before age 18 between 1950 and 2005 were DRB1 genotyped.

Results: Mean +/- SD age at diagnosis, 8.5 +/- 4.5 years, did not differ across decades. Recent diagnosis was associated with a lower proportion but unchanged incidence of the highest-risk DRB1 genotype DR3,4 (2000-2005, 28% vs. 1950-1969, 79%; P < 0.0001) and a higher proportion of lower-risk genotypes DR4,X and DR3,X (2000-2005, 48% vs. 1950-1969, 20%; P = 0.0002). The frequency of the DRX,X genotype was low (<or=3%) across decades. Recent birth was associated with a lower age at diagnosis for lower risk DR3,3 and DR4,4 (P < 0.0001) and DR4,X (P < 0.0001) and DR3,X (P = 0.015) genotypes but not for DR3,4.

Conclusions: The rising incidence and decreasing age at diagnosis of type 1 diabetes is accounted for by the impact of environment on children with lower-risk HLA class II genes, who previously would not have developed type 1 diabetes in childhood.

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Figures

Figure 1
Figure 1
The proportion of HLA-DRB1 genotypes in childhood-onset type 1 diabetes according to year of diagnosis (where X is a non-3 or non-4 DR allele). □, DR3,4; ▪, DR4,X and DR3,X.
Figure 2
Figure 2
Mean age at diagnosis of type 1 diabetes by decade of birth according to HLA-DRB1 genotypes. Error bars indicate the standard deviation.
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