Molecular profiling of different glioma specimens from an Ollier disease patient suggests a multifocal disease process in the setting of IDH mosaicism.

Ollier disease (OD) and Maffucci syndrome are rare conditions due to a post-zygotic somatic mutation that results in mosaicism. In addition to enchondromas and hemangiomas, some of these patients also develop other unrelated tumors, such as gliomas, that harbor IDH mutations, suggesting that an IDH mutation is a common genetic event in the tumorigenesis in this group of patients. We illustrate an interesting case of multifocal IDH-mutant astrocytomas in an OD patient with 8 years of follow-up. We first demonstrated identical IDH mutations in the brain tumor samples from various locations in this patient, but different 1p,19q results by fluorescent in-situ hybridization, different whole genome copy number profiles by OncoScan analysis, and a discrepant IDH2M131I mutation unique to one tumor, supporting a multifocal disease process in the setting of somatic IDH mosaicism.