Mutation of FGFR1 and MED12 of Cell-Free DNA Contribute to Early Diagnostics of Tumor-Induced Osteomalacia

Background: Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome with bone pain, fractures, and muscle weakness, which is mostly induced by phosphaturic mesenchymal tumors (PMTs). Owing to lacking sensitive detection techniques, the diagnosis of most TIO remains significantly delayed. Methods: As a case-control design, the plasma cell-free DNA (cfDNA) in four patients with TIO, four advanced cancer patients with bone metastasis (BM), and ten healthy controls were extracted and sequenced through a targeted next-generation sequencing approach. The comparison of mutation distribution and frequencies, and gene enrichment analysis was conducted between these groups. Findings: For the distributions of the allele frequencies, there was no obvious difference between the TIO and BM groups (p=0.946), while the differences between the case (TIO and BM) and the control groups were both extremely significant (both p<10-100). Similarly, for the mutation types, TIO and BM were closely alike (p=0.495) and healthy controls varied widely (p=3.05×10-58 and p=7.55×10-50, respectively). Despite the similarity of common mutations between TIO and BM groups, deleterious missense mutations within FGFR1 and loss-of-function mutations within MED12 were both found in 3/4 TIO patients while none of BM suffered. The gene ontology analysis strongly supported mutated genes found in TIOs would play a major role in PMTs process. Interpretation: As a proof-of-concept study, we reported the first study of the mutational landscape and genetic signature of the cell-free DNA in the TIO/PMTs. The early diagnosis of TIO can be achieved through specific biomarkers like deleterious mutations of FGFR1 and MED12 in cfDNA. Funding Statement: This research was funded in part by the National Natural Science Foundation of China (81472046 and 81772299 to Z.W., 81501852 to N.W., 81472045 and 81772301 to G.Q., and 81672123 to J.Z.), Beijing Natural Science Foundation (7172175 to N.W.), Beijing Nova Program (Z161100004916123 to N.W.,), Beijing Nova Program Interdisciplinary Collaborative Project (xxjc201717 to N.W.), 2016 Milstein Medical Asian American Partnership Foundation Fellowship Award in Translational Medicine (to N.W.), The Central Level Public Interest Program for Scientific Research Institute (2016ZX310177 to N.W.), PUMC Youth Fund & the Fundamental Research Funds for the Central Universities (3332016006 to N.W.), CAMS Initiative Fund for Medical Sciences (2016-I2M-3-003 to N.W., 2016-I2M-2-006 and 2017-I2M-2-001 to Z.W.), the Distinguished Youth Foundation of Peking Union Medical College Hospital (JQ201506 to N.W.), the 2016 PUMCH Science Fund for Junior Faculty (PUMCH-2016-1.1 to N.W.). Declaration of Interests: The authors have no conflict of interests to declare. Ethics Approval Statement: The study was reviewed and approved by the Ethics Committee of PUMCH.