Endocrine Abstracts

Patients with germline pathogenic variant (PV) in the SDHB gene (Paraganglioma syndrome type 4, PPGL4) have a high-risk of developing paragangliomas and pheochromocytomas. PPGL4 has increased risk for aggressive and metastatic abdominal-thoracic paragangliomas compared with other paraganglioma syndromes.

Aims: To assess possible germline DNA epigenetic alterations in patients harboring the SDHB PV.

Materials and Methods: Patients with PPGL4 were characterized clinically in our clinic and genetically via germline DNA sequencing for the familial variant (SDHB c.640C>T p.Q214Ter, n=144) and whole genome methylation analysis compared 19 patients vs 129 controls. The control group consisted of four SDHB PV-negative family members and 125 samples retrieved from a public database (GSE224359). Analysis was performed on Rstudio, using the ChAMP suite for normalization, imputation, differentially methylated probes (DMP), and regions (DMR) analyses. Pathway analysis and visualization were executed using the clusterprofiler and enrichplot packages. Promoter regions were defined by the transcription start site (TSS1500).

Results: The cohort includes three kindreds, presenting independently with an index patient: Index patient inkindred A, a 12-year-old boy, with thoracic paraspinal and testicular paragangliomas. Index patient inkindred B, a 26-year-old woman with abdominal paraganglioma, metastatic to the lungs and spine. Index patient inkindred C, a 41-year-old man with a locally aggressive abdominal paraganglioma, metastatic to the skull and spine. A total of 114 (44.2% females) patients underwent genetic evaluation (45/50, 16/28, and 25/36 in kindreds A, B and C, respectively). Of those, 50 (58.1%) harbored the familial SDHB PV (68.9%, 56.2%, and 40.0%, respectively). Twenty-six patients underwent at least partial clinical evaluation: eight had paraganglioma (4/8 had metastatic disease), three had pheochromocytoma, and two patients had neck masses that are currently being evaluated. Based on germline DNA promoter methylation data, SDHB PV carriers clustered separately from controls, including the SDHB PV non-carriers from the same kindred. No separation was demonstrated between patients that developed vs not developed PPGL at the time of the data collection. CpGs annotated to multiple genes were found differentially methylated between the groups. Of special interest are MGMT (encoding methyl guanine O-methyl transferase), and ARID1B (encoding AT-rich interactive domain-containing protein 1B) in the SDHB PV positive group.

Conclusions: We report one of the largest cohorts of PPGL4, showing typical low penetrance and aggressive phenotype. Genomic analysis shows distinct germline DNA methylation in SDHB PV-positive compared with the control group. Future studies may reveal an association between specific epigenetic alterations and penetrance/phenotypic patterns.