Association of sporadic chondrocalcinosis with a −4‐basepair G‐to‐A transition in the 5′‐untranslated region of ANKH that promotes enhanced expression of ANKH protein and excess generation of extracellular inorganic pyrophosphate

Abstract

Objective. Certain mutations in ANKH, which encodes a multiple-pass transmembrane protein that regulates inorganic pyrophosphate (PPi) transport, are linked to autosomal-dominant familial chondrocalcinosis. This study investigated the potential for ANKH sequence variants to promote sporadic chondrocalcinosis.Methods. ANKH variants identified by genomic sequencing were screened for association with chondrocalcinosis in 128 patients with severe sporadic chondrocalcinosis or pseudogout and in ethnically matched healthy controls. The effects of specific variants on expression of common markers were evaluated by in vitro transcription/translation. The function of these variants was studied in transfected human immortalized CH-8 articular chondrocytes.Results. Sporadic chondrocalcinosis was associated with a G-to-A transition in the ANKH 5-untranslated region (5-UTR) at 4 bp upstream of the start codon (in homozygotes of the minor allele, genotype relative risk 6.0, P ‫؍‬ 0.0006; overall genotype association P ‫؍‬ 0.02). This ؊4-bp transition, as well as 2 mutations previously linked with familial and sporadic chondrocalcinosis (؉14 bp C-to-T and C-terminal GAG deletion, respectively), but not the French familial chondrocalcinosis kindred 143-bp T-to-C mutation, increased reticulocyte ANKH transcription/ANKH translation in vitro. Transfection of complementary DNA for both the wild-type ANKH and the ؊4-bp ANKH protein variant promoted increased extracellular PPi in CH-8 cells, but unexpectedly, these ANKH mutants had divergent effects on the expression of extracellular PPi and the chondrocyte hypertrophy marker, type X collagen.Conclusion. A subset of sporadic chondrocalcinosis appears to be heritable via a ؊4-bp G-to-A ANKH 5-UTR transition that up-regulates expression of ANKH and extracellular PPi in chondrocyte cells. Distinct ANKH mutations associated with heritable chondrocalcinosis may promote disease by divergent effects on extracellular PPi and chondrocyte hypertrophy, which is likely to mediate differences in the clinical phenotypes and severity of the disease.

European League Against Rheumatism recommendations for calcium pyrophosphate deposition. Part I: terminology and diagnosis

“…The risk doubles every decade between 45 and 85 years (OR=2.25, 95% CI 1.79 to 2.82) independently of other risk factors 41. CPPD under age 45 should raise the possibility of familial42 18 43 or metabolic disease predisposition, especially if polyarticular. Gout is the main differential diagnosis of acute CPP crystal arthritis.…”

Calcifying tendinitis of the shoulder: Advances in imaging and management

“…Because there is no entirely clear relation among ANKH and TNAP genes and crystal deposition, this mutation will only be part of the story. Zhang et al [15], in their basic research project on heritable chondrocalcinosis, noted that distinct ANKH mutations associated with heritable chondrocalcinosis may promote disease by divergent effects on extracellular inorganic pyrophosphate and chondrocyte hypertrophy, which may mediate differences in the clinical phenotypes and severity of the disease.…”

P5L mutation in Ank results in an increase in extracellular inorganic pyrophosphate during proliferation and nonmineralizing hypertrophy in stably transduced ATDC5 cells

“…Recent studies of transient transfection of a familial (P5L [17]) ANKH mutation and two ANKH variants (-4 bp, 5' untranslated region [31] and deletion of E490 [15]) in an immortalized human chondrocyte cell line (CH-8) demonstrated an increase in the transcription and translation of ANK. Among the two missense ANKH mutants studied, neither the P5L mutant nor the M48T mutant demonstrated an increase in ePPi elaboration [31].…”