Mutations and polymorphisms in the SDHB, SDHD, VHL, and RET genes in sporadic and familial pheochromocytomas
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The prevalence of germ line mutations within the RET-protooncogene and the tumor suppressor genes SDHB, SDHD, and VHL in pheochromocytomas (PC) varies in recent studies from 12 to 24%, if one look at them collectively. DNA was extracted from frozen tumor tissue as well as from blood leukocytes of 36 PC (26 sporadic/10 MEN2). Exons 1-8 of the SDHB-gene, 1-4 of the SDHD-gene, 1-3 of the VHL-gene, and exons 10, 11, 13, 14, 16 of the RET-gene were amplified by PCR and analyzed by DHPLC with the Transgenomic WAVE®-System. Samples with aberrant wave profiles were subjected to direct sequencing. Genetic aberrations were correlated to clinical characteristics. Germ line mutations in sporadic PC were identified in four patients (11%) whereas somatic mutations were observed in two (5%) patients. Nine coding polymorphisms (PM) were identified in seven (19%) patients. Intronic variants were observed in six (17%) patients and were all located in the SHDB gene. Patients with wild type alleles in all assessed genes were older (53 vs. 37 years, P = 0.007) and presented with an increased tumor size (49 vs. 32 mm, P = 0.003) compared to patients with mutations. Malignant PC revealed multiple (>2) genetic alterations more frequently than benign PC (4/7 vs. 4/29, P = 0.03). Interestingly intronic variants of the SDHB gene occur more frequently in malignant than in benign PC (3/7 vs. 2/29, P = 0.04). The frequency of germ line mutations in sporadic pheochromocytomas was lower in our cohort than previously reported. Polymorphisms of the RET gene are common (17%) and occur in familial and sporadic PC. Multiple genetic alterations including mutations, polymorphisms and intronic variants are more frequently observed in malignant PC.