C9ORF72 hexanucleotide repeat expansion frequency in patients with Paget's disease of bone.

Paget's disease of bone (PDB) is a focal bone disorder affecting the skeleton segmentally. A strong genetic component has been shown in PDB, and variants in several genes, such as SQSTM1, VCP, and OPTN, have been associated with the disease. Mutations in the same genes have also been reported in patients with frontotemporal dementia and amyotrophic lateral sclerosis. Hexanucleotide repeat expansions in the C9ORF72 gene have been shown to be responsible for both familial and sporadic frontotemporal dementia/amyotrophic lateral sclerosis. Thence, we evaluated the frequency of the C9ORF72 hexanucleotide repeat expansions in a cohort of 191 Italian PDB patients and in 106 controls. The pathogenic repeat expansion was detected in 2 PDB patients (1.0%). During the follow-up period, both PDB patients did not develop any sign of mental decline and/or motor neuron disease. Our study suggests that repeat expansions in the C9ORF72 gene are rare in patients with PDB.