Different genetic pathways in the development of periocular sebaceous gland carcinomas in presumptive Muir-Torre syndrome patients

Abstract

Periocular sebaceous gland carcinomas (SGCs) occur in the eyelids either sporadically or as a phenotypic feature of Muir-Torre syndrome (MTS). In knockout mice mismatch-repair (MMR) defects or inactivation of the fragile histidine triad (FHIT) gene are associated with MTS-like signs, including SGC. To dissect the genetic alterations associated with microsatellite instability (MSI) and inactivation of the FHIT gene, we studied nine periocular SGC specimens from MTS patients. Immunohistochemistry was performed for FHIT, MSH2, MLH1, and MSH6. We assessed MSI as well as loss of heterozygosity (LOH) at the FHIT locus with polymorphic markers and genomic multiplex PCR. Epigenetic silencing was detected by methylation-specific PCR (MSP) and combined bisulfite restriction analysis (COBRA). Our analyses identified two SGCs with FHIT positivity and high-grade MSI, and seven cases with loss of FHIT and microsatellite stability (MSS). MSI correlated with loss of MSH2 and MLH1 immunostaining. Loss-of-function mechanisms affecting the FHIT gene were identified as intragenic deletions eliminating the coding exons 5 and 6 on one hand, and complete biallelic methylation of the FHIT transcription regulatory region on the other hand. Germinal FHIT mutations as a predisposing factor for MTS were excluded in two index patients with cancer in three generations, including an FHIT-negative SGC. Our data suggest that either somatic inactivation of the FHIT gene associated with MSS or inactivation of the MMR system resulting in MSI contribute to the development of periocular SGCs in presumptive MTS.