A Systematic Investigation of PIK3CA Mutations in Isolated Macrodactyly: Indication for Accurate Classification, Diagnosis and Potential Novel Therapeutics

Abstract

Grant received from: Beijing Talent Funding There is no financial information to disclose. Macrodactyly, a rare congenital digital anomaly, has been challenging the hand surgery society. The recent discovery of somatic PIK3CA mutations in a few isolated macrodactyly patients shed light on the fundamental understanding in pathogenesis of this disabling deformity. We set up to systematically test the association between PIK3CA mutations with isolated macrodactyly in order to establish a molecular pathophysiology-based diagnosis, classification and possibly a novel therapeutic strategy. Overgrowth tissues including skin, nerve, adipose tissues from clinically diagnosed isolated macrodactyly patients (N = 12) were removed during routine surgical debulking or correction procedures and preserved as formalin-fixed-paraffin-embedded (FFPE) blocks. DNA recovered from these FFPE samples were tested for PIK3CA mutation status using a modified and targeted Sanger DNA sequencing method with greatly improved sensitivity for detecting low level somatic mosaic mutations. PIK3CA mutation level, tissue(s) of occurring, type of mutations and their genomic locations were analyzed. PIK3CA mutations were detected from affected tissues in 9 out of the 12 patients studied, with mutation level ranging from 8 to 27%. The mutations detected include p.His1047Arg (N = 4), p.His1047Leu (N = 2), p.545Glu > Lys (N = 2) and p.542Glu > Lys (N = 1). These are codons in the PIK3CA gene that are frequently mutated in cancers. In terms of the tissue sources in which a mutation was found, adipose tissue has the highest mutation detection rate (100%), followed by nerve (83%) and skin (71%). No mutations found in bone tissues from two patients with PIK3CA mutations detected in other tissues of the same patients. Patients and/or tissues negative for PIK3CA mutations are subjected to downstream analysis using high throughput next generation DNA sequencing. (Figs. 40-1, 40-2) •A high proportion (75%) of isolated macrodactyly patients harbors activating PIK3CA mutations that lead to digital overgrowth as a result of abnormally activated Akt-PI3K signaling.•Adipose and nerve tissues provide the highest PIK3CA mutation detection yield among all the sources of affected tissues.•A modified Sanger DNA sequencing method is a cost-effective way to exam PIK3CA mutations in isolated macrodactyly patients clinically.•Patients negative for PIK3CA mutations may harbor other PIK3CA mutations beyond the detection of our assay or due to different molecular mechanism.•To our knowledge, our study is the largest study linking PIK3CA mutations to isolated macrodactyly.Figure 40-2PIK3CA mutations in isolated macrodactyly patients. PIK3CA gene structure with critical domains, targeted regions, and mutations identified in isolated macrodactyly patients are summarized. Red arrows indicate three targeted regions (p.418-435, p.527-555, and p.1009-1058) by Sanger DNA sequencing. Mutations previously reported and numbers of patients are depicted above the gene structure and those found in our patients are shown under. Cancer hotspot mutations are highlighted in red.View Large Image Figure ViewerDownload Hi-res image Download (PPT)