Molecular characterization of novel germline deletions affecting SDHD and SDHC in pheochromocytoma and paraganglioma patients

Abstract

A major cause of paraganglioma and pheochromocytoma is germline mutation of the tumor suppressor genes SDHB, SDHC, and SDHD, encoding subunits of succinate dehydrogenase (SDH). While many SDH missense/nonsense mutations have been identified, few large deletions have been described. We performed multiplex ligation-dependent probe amplification deletion analysis in 126 point mutation-negative patients, and here we describe four novel deletions of SDHD and SDHC. Long-range PCR was used for the fine mapping of deletions. One patient had a 10 kb AluSg–AluSx-mediated deletion including SDHD exons 1 and 2, the entire TIMM8B gene, and deletion of exons of C11orf57. A second patient had a deletion of SDHD exons 1 and 2 and exon 1 of the TIMM8B gene. A third patient showed a deletion of exon 2 of SDHD, together with a 235 bp MIRb–Tensin gene insertion. In a fourth patient, a deletion of exons 5 and 6 of the SDHC gene was found, only the second SDHC deletion currently known. The deletions of the TIMM8B and C11orf57 genes are the first to be described, but do not appear to result in an additional phenotype in these patients. Four of the eight breakpoints occurred in Alu sequences and all three SDHD deletions showed an intron 2 breakpoint. This study underlines the fact that clinically relevant deletions may encompass neighboring genes, with the potential to modify phenotype. Gene deletions of SDHD and SDHC represent a substantial proportion of all mutations, and must be considered in paraganglioma patients shown to be negative for mutations by sequencing.