MUTATIONS IN A PYROPHOSPHATE CHANNELLING GENE IN PATIENTS WITH CUFF TEAR ARTHROPATHY

Abstract

Progressive arthritis can occur in association with massive tears of the rotator cuff. Altered joint kinematics are commonly proposed as the principle causative factor but this does not explain the absence of arthropathy in some patients. We have investigated the role of the ANKH gene in patients with cuff tear arthropathy. The transmembrane protein ANKH promotes intracellular to extracellular inorganic pyrophosphate channelling which regulates calcium pyrophosphate dihydrate and hydroxyapatite crystal deposition. Genomic DNA was prepared from peripheral blood leucocytes from 20 patients with cuff tear arthropathy diagnosed clinically and radiologically and 24 healthy matched controls. All 12 exons and exon-intron boundaries from the ANKH gene were PCR amplified and sequenced with BigDye version 3.1 terminator kit (ABI), and analysed using ABI PRISM ® 3100 Genetic Analyser. We have identified 5 single nucleotide polymorphisms (SNPs) including 4 that have previously been identified in patients with chondrocalcinosis. These are in exon 2 (GCC†’GCT 294), intron 2 (G†’A +8), exon 8 (GCA†’GCG 963) and intron 8 (T†’G +15). We also identified an A†’G variant in 3′-UTR, 30 base pairs after the stop codon which has not been reported before in crystal deposition diseases, and is also not seen in any of the healthy controls. Further elucidation is necessary to demonstrate a causal relationship between these ANKH mutations and cuff tear arthropathy, which will add to our understanding of pathogenic mechanisms in this condition.