Identification of CANT1 mutations in Desbuquois dysplasia

Abstract

Desbuquois dysplasia is a severe condition characterized by short stature, joint laxity, scoliosis, and advanced carpal ossification with a delta phalanx. Studying nine Desbuquois families, we identified seven distinct mutations in the Calcium-Activated Nucleotidase 1 gene (CANT1), which encodes a soluble UDP-preferring nucleotidase belonging to the apyrase family. Among the seven mutations, four were nonsense mutations (Del 5' UTR and exon 1, p.P245RfsX3, p.S303AfsX20, and p.W125X), and three were missense mutations (p.R300C, p.R300H, and p.P299L) responsible for the change of conserved amino acids located in the seventh nucleotidase conserved region (NRC). The arginine substitution at position 300 was identified in five out of nine families. The specific function of CANT1 is as yet unknown, but its substrates are involved in several major signaling functions, including Ca2+ release, through activation of pyrimidinergic signaling. Importantly, using RT-PCR analysis, we observed a specific expression in chondrocytes. We also found electron-dense material within distended rough endoplasmic reticulum in the fibroblasts of Desbuquois patients. Our findings demonstrate the specific involvement of a nucleotidase in the endochondral ossification process.

Figure 1

Radiological Manifestations of Desbuquois Dysplasia (A and B) Hand X-rays at 1 and 3 years of age. Note the advanced carpal ossification and the delta phalanx (arrow). (C) Hip at 3 years of age. Note the Swedish key appearance of the proximal femur. (D) Knee at 3 years of age. Note the metaphyseal irregularities.

Figure 2

CANT1 Mutations Identified in Desbuquois Patients Position of the primers used for the RT-PCR.

Figure 3

CANT1 mRNA Expression by RT-PCR in Desbuquois Patient Lymphocytes and Fibroblasts and in Wild-Type Chondrocytes and Osteoblasts

Figure 4

Transmission Electron Microscopy in Fibroblasts from Three Desbuquois Dysplasia Patients (A–C) RER cisternae appeared markedly dilated in the vast majority of cells, in which there was an accumulation of slightly electron-dense, fibrillar, or finely granular proteinaceous material (arrows). Interestingly, there is no evidence of ribosome detachment, commonly observed in severe oxidative stress. (D) Cultured fibroblasts from healthy individuals failed to display significant enlargement of RER (arrowhead). (staining was with uranyl acetate and lead citrate; original magnification ×15,000).