Endocrine Abstracts

Introduction: Pheochromocytomas and paragangliomas (Pheo/PGL) are rare neuroendocrine tumours arising from the adrenal medulla or the symphathetic paraganglia, respectively. Germline mutations are present in ~40% of the patients. To date, at least 16 genes have been demonstrated to be involved in the genetic background of Pheo/PGL. Prioritization in order of genes tested can be applied, but if the probability of a disease-associated germline mutation exceeds 10% the testing of all susceptibility genes is recommended. Using next generation sequencing (NGS) based methods for genetic testing of Pheo/PGL associated genes progressively becomes part of the routine diagnostics.

Objective: To assess the genetic background of Hungarian patients with Pheo/PGL and to develop a NGS based gene panel assay for analysis of Pheo/PGL susceptibility genes.

Methods: We examined 131 patients with the diagnosis of Pheo/PGL diagnosed and nursed at the 2nd Department of Medicine, Semmelweis University. The prevalence of the germline mutations of Pheo/PGL genes was determined using conventional methods. Genotype-phenotype correlations were evaluated. A gene panel covering 15 genes (RET, VHL, NF1, EPAS, EGLN1, KIF1B, SDHA, SDHB, SDHAF2, SDHC, SDHD, FH, MAX, TMEM127, MEN1) was developed and analytical sensitivity was evaluated on 36 patients with known genetic background. Library preparation was performed using SeqCapEZ capture platform with our probe design. Illumina MiSeq instrument was used for sequencing. Sequencing data were analysed with GATK workflow. Variant annotation was performed with SNPeffect.

Results: Germline mutations of Pheo/PGL genes were present in at 34% of the patients: 10 (7.6%) SDHB, 9 (6.9%) RET, 5 (3.8%) VHL, TMEM127, MDH2, 4 (3%) NF1, 3 (2.3%) SDHD, 2 (1.5%) SDHC and KIF1B. 5 of 10 SDHB mutation carriers developed malignant disease. Homozygous form of a MDH2 variant was associated with malignancy. Among the 10 patients with bilateral adrenal Pheo 4 RET, 2 TMEM127 and 1 VHL mutations were identified. The coverage of genes in our panel was higher than 150 reads in all regions and all known mutations were correctly identified.

Discussion: Our findings regarding the prevalence of germline mutations in the development of Pheo/PGL are in accordance with the literature. No founder mutation occurred in our population as we could detect mutations in 9 genes, underlining the need of novel methods for mutation analysis in everyday clinical practice. Our NGS-based gene panel performed accurately, however two recently identified genes (MDH2, GOT2) were not covered.