6912 Nail Fold Capillary Findings In Patients With Somatic EPAS1 Pathogenic Variants

Abstract Disclosure: H. Alkaissi: None. B. Turturice: None. J. S. Rosenblum: None. A. S. Alzahrani: None. S. Talvacchio: None. A. Derkyi: None. M. Nazari: None. H. Wang: None. I. Pinal Fernandez: None. Z. Zhuang: None. K. Pacak: None. We recently discovered a new syndrome characterized by a triad of pheochromocytoma/paraganglioma, polycythemia, and somatostatinoma (so called Pacak-Zhuang syndrome) caused by somatic gain-of-function pathogenic variants in the EPAS1 gene, encoding hypoxia-inducible factor 2α (HIF-2α). Recently, we have described additional features of this syndrome, including systemic developmental vascular malformations in patients and the mouse model 1. Here we evaluated vascular changes in the nailfold capillaries by using video capillaroscopy in four patients, three of whom were female and carried the same pathogenic somatic EPAS1 variant allele (EPAS1A530V). The first patient is an 18-year-old female with a history of ventricular septal defect since birth, acrocyanosis, abdominal paraganglioma, left adrenal pheochromocytoma, and polycythemia. The second patient is a 64-year-old female who presented with paraganglioma without polycythemia, in whom we found the EPAS1A530V variant from hair sample, and an additional variant (EPAS1P531A) in a resected paraganglioma, confirming the diagnosis. The third patient is a 33-year-old female had polycythemia, right adrenal pheochromocytoma, abdominal paragangliomas and duodenal somatostatinoma. The fourth patient is a 25-year-old male with PZS bearing a somatic EPAS1M535V pathogenic variant and an additional D536L542 deletion, with hypoplastic left ventricle and metastatic paraganglioma who never developed polycythemia due to concomitant sickle cell-thalassemia traits. Despite the notable differences in genotype between the first three patients compared to the fourth patient, whose genotype is more complex, nailfold video capillaroscopy of all these patients showed similar phenotype—abnormal capillary structure marked by widespread dilations, megacapillaries, sporadic capillary hemorrhages, and regions with diminished capillary density. While polycythemia has been implicated in megacapillaries phenotype, two of our patients did not have polycythemia at the time of evaluation, further supporting the role of HIF-2a in angiogenesis. In conclusion, we describe nailfold capillary changes on video capillaroscopy as a non-invasive clinical sign in patients with EPAS1 pathogenic variants. Whether this finding is due to circulating angiogenic factors secreted by the tissues harboring HIF-2α mutation, or a direct effect of HIF-2α on angiogenesis remains to be determined. References: 1. Rosenblum JS, Wang H, Dmitriev PM, Cappadona AJ, Mastorakos P, Xu C, Jha A, Edwards N, Donahue DR, Munasinghe J, Nazari MA, Knutsen RH, Rosenblum BR, Smirniotopoulos JG, Pappo A, Spetzler RF, Vortmeyer A, Gilbert MR, McGavern DB, Chew E, Kozel BA, Heiss JD, Zhuang Z, Pacak K. Developmental vascular malformations in EPAS1 gain-of-function syndrome. Presentation: 6/2/2024