Head and Neck Paraganglioma in Pacak-Zhuang Syndrome.

Head and neck paragangliomas (HNPGLs) are typically slow-growing, hormonally inactive tumors of parasympathetic paraganglia. Inactivation of prolyl-hydroxylase domain-containing 2 protein causing indirect gain-of-function of hypoxia-inducible factor-2α (HIF-2α), encoded by EPAS1, was recently shown to cause carotid body hyperplasia. We previously described a syndrome with multiple sympathetic paragangliomas caused by direct gain-of-function variants in EPAS1 (Pacak-Zhuang syndrome, PZS) and developed a corresponding mouse model. We evaluated a cohort of patients with PZS (n = 9) for HNPGL by positron emission tomography, magnetic resonance imaging, and computed tomography and measured carotid body size compared to literature reference values. Three patients had imaging consistent with HNPGL, one of which warranted resection and was confirmed on histology. Three additional patients had carotid body enlargement (Z-score > 2.0), and three had carotid artery malformations. Using high resolution ex vivo imaging and histology, we found that nine of ten adult mutant mice had carotid body tumors and six of eight had a paraganglioma on the cranio-caval vein, the murine homologue of the superior vena cava; these were also found in four of five mutant mice at post-natal day 8. These tumors and the one resected from a patient were positive for tyrosine hydroxylase, synaptophysin, and chromogranin A. Brown fat in a resected patient tumor carried the EPAS1 pathogenic variant. These findings 1) suggest HNPGL as a feature of PZS and 2) show that these pathogenic variants are sufficient to cause the development of these tumors, which we believe represents a continuous spectrum of disease starting from hyperplasia.