Large Germline Deletions of Mitochondrial Complex II Subunits SDHB and SDHD in Hereditary Paraganglioma

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Abstract
More than 30% of adrenal pheochromocytomas are hereditary. These neuroendocrine tumors are major components of three inherited cancer syndromes: multiple endocrine neoplasia type 2, von Hippel-Lindau disease (VHL), and pheochromocytoma/paraganglioma syndrome (PC/PGL). Germline mutations in RET; VHL; and SDHB, SDHC, and SDHD are associated with multiple endocrine neoplasia type 2, VHL, and PC/PGL, respectively. The majority (>70%) of hereditary extraadrenal PCs [catecholamine-secreting paragangliomas (PGL)] are accounted for by germline intragenic mutations in SDHB, SDHC, or SDHD. Therefore, a subset of hereditary PGL is not accounted for. Here we report two unrelated hereditary PGL families, one with a germline whole-gene deletion of SDHD (family 4194), the other a partial deletion of SDHB (family BRZ01). Although they were initially designated mutation negative for all of the PC-associated genes after PCR-based analysis, we suspected that a large deletion or rearrangement might be present. Genotyping around the PC-associated genes demonstrated that both families were consistent with linkage with one of these genes. Using fine structure genotyping and semiquantitative duplex PCR analysis, we identified an approximately 96-kb deletion spanning SDHD in family 4194 and an approximately 1-kb deletion involving the 5' end of SDHB in family BRZ01. Thus, including SDHB and SDHD deletion analysis could increase gene-testing sensitivity for PGL patients, which would aid in genetic counseling and management of patients and families.