Whole exome sequencing of patients with diffuse idiopathic skeletal hyperostosis and calcium pyrophosphate crystal chondrocalcinosis.

Objectives: DISH/CC is a poorly understood phenotype characterised by peripheral and axial enthesopathic calcifications, frequently fulfilling the radiological criteria for Diffuse Idiopathic Skeletal Hyperostosis (DISH, MIM 106400), and in some cases associated with Calcium Pyrophosphate Dihydrate (CPPD) Chondrocalcinosis (CC). The concurrence of DISH and CC suggests a shared pathogenic mechanism. In order to identify genetic variants for susceptibility we performed whole exome sequencing in four patients showing this phenotype.

Materials and methods: Exome data were filtered in order to find a variant or a group of variants that could be associated with the DISH/CC phenotype. Variants of interest were subsequently confirmed by Sanger sequencing. Selected variants were screened in a cohort of 65 DISH/CC patients vs 118 controls from Azores. The statistical analysis was performed using PLINK V1.07.

Results: We identified 21 genetic variants in 17 genes that were directly or indirectly related to mineralization, several are predicted to have a strong effect at a protein level. Phylogenetic analysis of altered amino acids indicates that these are either highly conserved in vertebrates or conserved in mammals. In case-control analyses, variant rs34473884 in PPP2R2D was significantly associated with the DISH/CC phenotype (p=0.028; OR=1.789, 95% CI= 1.060 - 3.021)).

Conclusion: The results of the present and preceding studies with the DISH/CC families suggests that the phenotype has a polygenic basis. The PPP2R2D gene could be involved in this phenotype in an as yet unknown way.