Study of the association between the CAPSL-IL7R locus and type 1 diabetes

In the past few years, several genes outside the MHC region have been described as new susceptibility genetic factors to type 1 diabetes. An association between CAPSL-rs1445898 and type 1 diabetes was reported in a large white population and corroborated in a genome-wide analysis, which also found an association with IL7R, which is located adjacent to CAPSL. The aim of this study was to replicate the aforementioned associations in independent cohorts.

We analysed two CAPSL (rs1010601 and rs1445898) and three IL7R (rs6897932, rs987106 and rs3194051) polymorphisms. All these single nucleotide polymorphisms (SNPs) were genotyped using TaqMan minor groove binder chemistry in 301 unrelated Spanish type 1 diabetes patients and 646 healthy controls. Additionally, the associated CAPSL SNP rs1445898 was genotyped in a Dutch cohort consisting of 429 type 1 diabetes patients and 720 healthy controls.

The homozygous mutant genotype of the CAPSL SNP rs1445898 showed a trend towards a protective effect in the overall Spanish cohort (OR [95% CI] 0.70 [0.44-1.09]; p = 0.09) and in the Dutch cohort (OR [95% CI] 0.74 [0.51-1.05]; p = 0.09). Pooling of both cohorts was performed, yielding a statistically significant difference (Mantel-Haenszel OR 0.71; p = 0.005). This protective effect was significantly different in early-onset vs late-onset Spanish patients (OR [95% CI] 0.26 [0.10-0.65]; p = 0.001). Similarly, in the early-onset subgroup, the homozygous mutant genotype of the IL7R SNP rs6897932 showed a similar protective effect (OR [95% CI] 0.18 [0.02-0.94]; p = 0.02).

In summary, we describe an independent replication of the association between the CAPSL-IL7R locus and type 1 diabetes, especially for early-onset type 1 diabetes patients.