We have recently described the association between rheumatoid arthritis and a coding single-nucleotide polymorphism in the intracellular protein tyrosine phosphatase, PTPN22. The disease-associated polymorphism, 1858 C/T (rs2476601), encodes an amino-acid change (R620W) in one of four SH3 domain binding sites in the PTPN22 molecule. We have now extended our initial studies to address three questions: (1) Is the association with rheumatoid arthritis limited to rheumatoid factor (RF) positive disease? (2) Does homozygosity for PTPN22 R620W substantially increase disease susceptibility? (3) Is there an interaction between PTPN22 and the rheumatoid arthritis (RA)-associated HLA-DRB1 shared epitope alleles? A total of 1413 Caucasian rheumatoid arthritis patients and 1401 Caucasian controls were genotyped. The results support the view that PTPN22 was strongly and preferentially associated with RF positive disease (OR ¼ 1.75, 95% CI 1.46-2.10, P ¼ 1.3 Â 10 À9 ). The PTPN22 risk allele was not significantly associated with RF negative disease (OR ¼ 1.19, 95% CI 0.92-1.53, P ¼ 0.18), although a very weak association cannot be completely excluded. There was a strong dose effect on disease risk; two copies of the PTPN22 R620W allele more than doubles the risk for RF positive RA (OR ¼ 4.57, 95% CI 2.35-8.89). There was no evidence of a genetic association between PTPN22 and HLA susceptibility alleles.

SummaryMicrotia is a congenital malformation of the external ear that can be observed in many species including sheep. However, the genetic basis of microtia still remains unclear. Here, a GWAS was conducted to investigate the genetic basis underlying microtia. A total of 55 samples from 26 microtia and 29 normal animals were genotyped with Illumina OvineHD BeadChip. The strongest significant SNP was identified on OAR6, approximating the evolutionarily conserved region of the HMX1 gene, which is related to congenital malformations of the external ear in other species such as cattle and rats. Sequencing an evolutionarily conserved region surrounding HMX1 revealed a duplication of 76 bp, which is concordant with microtia, suggesting a dominant inheritance mode. Identification of this causal mutation in the HMX1 gene indicates the role of this particular gene in the development of the external ear and provides a genetic marker for selection against microtia.