Bone Abstracts

Introduction: Paget’s disease of bone (PDB) has an autosomal-dominant mode of inheritance in one-third of cases. The germinal SQSTM1/P392L mutation is the most frequent mutation, present in 40% of patients with a familial form of PDB, and 8% of unrelated patients. Fibrous dysplasia (FD) is a rare bone disorder, mono or polyostotic, caused by post-zygotic mutations in GNAS gene, for which a PCR-clamping method was developed to ease their detection and avoid bone biopsies. Given the focal nature of PDB, this study aimed at optimizing this PCR-clamping method to search for SQSTM1/P392L post-zygotic mutations in peripheral blood of PDB patients.

Methods: We optimized the PCR method in nine FD patients with a locked nucleic acid (LNA) specific for the GNAS/R201L mutation, which blocks the wild-type allele amplification. Thereafter, we optimized the PCR method in PDB patients, using a LNA specific for the SQSTM1/P392L mutation, and we analyzed 210 unrelated PDB patients non carrier of a germinal SQSTM1/P392L mutation. We compared PDB patients with post-zygotic mutation to unrelated patients with germinal mutation (n=21) and without mutation (n=203) for age at diagnosis, sex, number of affected bones, Renier’s index (an anatomical index measuring the PDB extent), and total alkaline phosphatase levels.

Results: We found, for the reference post-zygotic GNAS/R201L mutation, one carrier among FD patients. Seven (3.3%) unrelated PDB patients carried a SQSTM1/P392L post-zygotic mutation. PDB patients with a SQSTM1/P392L post-zygotic mutation had a Renier’s index lower than patients carrying a germinal mutation (6.9±4.1 vs 15.5±10.4, P=0.046) and had a younger age at diagnosis than patients without mutation (53.0±13.9 vs 63.5±10.8 years, P=0.05).

Conclusion: This study confirmed that PCR-clamping increases the sensitivity of detection of SQSTM1/P392L post-zygotic mutations which may occur in unrelated patients with PDB. Further analyses are required to understand the functional consequences of this post-zygotic mutation in PDB.