Identification of an Amino Acid Motif in HLA-DRß1 That Distinguishes Uveitis in Patients With Juvenile Idiopathic Arthritis.

OBJECTIVE: Uveitis is a visually debilitating disorder that affects up to 30% of children with the most common forms of juvenile idiopathic arthritis (JIA). The disease mechanisms predisposing only a subgroup of children to uveitis are unknown. This study was undertaken to identify genetic susceptibility loci for uveitis in JIA, using a genome-wide association study in 522 children with JIA. METHODS: Two cohorts of JIA patients with ophthalmologic follow-up data were genotyped. Data were then imputed using a genome-wide imputation reference panel, and an HLA-specific reference panel was used for imputing amino acids and HLA types in the major histocompatibility complex (MHC). After imputation, genome-wide and MHC-specific analyses were performed, and a reverse immunology approach was utilized to model antigen presentation at 13 common HLA-DRß1 alleles. RESULTS: Presence of the amino acid serine at position 11 (serine 11) in HLA-DRß1 was associated with an increased risk of uveitis in JIA patients (odds ratio [OR] 2.60, P = 5.43 × 10-10 ) and was specific to girls (Pfemales = 7.61 × 10-10 versus Pmales = 0.18). Serine 11 resides in the YST motif in the peptide-binding groove of HLA-DRß1; all 3 amino acids in this motif are in perfect linkage disequilibrium and show identical association with disease. Quantitative prediction of binding affinity revealed that HLA-DRß1 alleles with the YST motif could be distinguished on the basis of discernable peptide-binding preferences. CONCLUSION: These findings highlight a genetically distinct, sexually dimorphic feature of JIA with uveitis as compared to JIA without uveitis. The association could be indicative of the potential involvement of antigen presentation by HLA-DRß1 in the development of uveitis in JIA. The results of this study may advance our progress toward improved treatments for, and possible prevention of, the sight-threatening complications of uveitis in children with JIA.

The natural history of a combined defect in MSH6 and MUTYH in a HNPCC family.

In the inherited syndromes, MUTYH-associated polyposis (MAP) and hereditary nonpolyposis colorectal cancer (HNPCC), somatic mutations occur due to loss of the caretaker function that base-repair (BER) and mismatch repair (MMR) genes have, respectively. Recently, we identified a large branch from a MSH6 HNPCC family in which 19 family members are heterozygous or compound heterozygous for MUTYH germ line mutations. MSH6/MUTYH heterozygote mutation carriers display a predominant HNPCC molecular tumour phenotype, with microsatellite instability and underrepresentation of G>T transversions. A single unique patient is carrier of the MSH6 germline mutation and is compound heterozygote for MUTYH. Unexpectedly, this patient has an extremely mild clinical phenotype with sofar only few adenomas at age 56. Four out of five adenomas show characteristic G>T transversions in APC and/or KRAS2, as seen in MUTYH associated polyposis. No second hit of MSH6 is apparent in any of the adenomas, due to retained MSH6 nuclear expression and a lack of microsatellite instability. Although this concerns only one case, we argue that the chance to find an additional one is extremely small and currently a mouse model with this genotype combination is not available. Moreover, the patients brother who is also compound heterozygous for MUTYH but lacks the MSH6 germline mutation presented with a full blown polyposis coli. In conclusion, these data would support the notion that abrogation of both MSH6 DNA mismatch repair and base repair might be mutually exclusive in humans.