Somatic IDH1 variant (p.R132C) in an adult male with Maffucci syndrome

Abstract

Maffucci Syndrome is a rare, highly variable somatic mosaic condition and well-known cancer related gain-of-function variants in either the IDH1 or IDH2 genes have been found in the affected tissues of most reported patients. Features include benign enchondroma and spindle cell hemangioma, with a recognized increased risk of various malignancies. Fewer than 200 cases have been reported, therefore accurate estimates of malignancy risk are difficult to quantify and recommended surveillance guidelines are not available. The same gain-of-function IDH1 and IDH2 variants are also implicated in a variety of other benign and malignant tumors. An adult male presented with several soft palpable lesions on the right upper limb. Imaging and histopathology raised the possibility of Maffucci syndrome. DNA was extracted from peripheral blood lymphocytes and tissue surgically resected from a spindle-cell hemangioma. Sanger sequencing and Droplet-digital PCR analysis of the IDH1 gene was performed. We identified a somatic mosaic c.394C>T (p.R132C) variant in exon 5 of IDH1, in DNA derived from hemangioma tissue at ~ 17% mutant allele frequency. This variant was absent in DNA derived from blood. This variant has been identified in the affected tissue of most reported patients with Maffucci syndrome Although the patient has a potentially targetable variant, and there is a recognized risk of malignant transformation in this condition, a decision was made not to intervene with an IDH1 inhibitor. The reasons and prospects for therapy in this condition are discussed.