A Novel Splice Site IRP1 Mutation Associated with Pheochromocytoma-Polycythemia Syndrome

Presentation Number: SUN 360
Date of Presentation: April 2nd, 2017

Ying Pang*1, Garima Gupta2, Chunzhang Yang1, Herui Wang1, Ziedulla Abdullaev3, Svetlana D. Pack3, Zhengping Zhuang4 and Karel Pacak1
1National Institutes of Health, Bethesda, MD, 2National Institutes of Health, bethesda, MD, 3National Institutes of Health, Bethesda, 4National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD

Abstract

Background: Recent discoveries of genetic mutations causing upregulation of the hypoxia signaling pathway, including HIF2A, VHL, and PHD1/2 have been reported as players in the pathogenesis of pheochromocytoma/paraganglioma (PHEO/PGL)-polycythemia syndrome. However, some patients presenting with both of these diagnoses test negative for these well-known genetic mutations, indicating towards other undiscovered genetic/pathogenetic factors.

Clinical Case:

A 47-year-old female was referred due to history of a right-sided PHEO, diagnosed and resected at age 42. Her symptoms prior to diagnosis included episodes of elevated blood pressure, palpitations, diaphoresis, abdominal pain, nausea, and vomiting. Initial diagnostic work-up revealed elevated levels of urinary norepinephrine, dopamine, and normetanephrine with a 4.5 cm lesion in the right adrenal gland identified on CT. Furthermore, patient was diagnosed with polycythemia of unclear etiology at age 37 after presenting with classic clinical symptoms of aquagenic pruritus, facial plethora, excessive sweating, joint pain, fatigue and headache. Preoperatively, her hematocrit levels ranged between 46.5–50.9 % [normal: 35-45%] with transient improvement postoperatively. Erythropoietin (EPO) levels were not investigated prior to surgery but were within the normal reference range postoperatively.

Genetic testing for mutations in the well-known PHEO susceptibility genes associated with this syndrome was negative. Due to unclear etiology of the secondary polycythemia seen in the patient, we performed further testing and discovered two heterozygous mutations (c.267-1G>T; c.267G>A) at the exon 3 splice site of iron regulatory protein 1 (IRP1) gene, which is a negative regulator of HIF-2α. ini gene construct and splicing site analysis showed the mutations caused novel splicing site formation and frameshift mutation of IRP1. Fluorescence in situ hybridization analysis demonstrated heterozygous IRP1 gene deletions and immunohistochemistry showed loss of the IRP1 protein and HIF-2α over expression in tumor cells. Furthermore, protein levels of EPO and EPO receptor in the tumor were found to be upregulated on immunohistochemistry compared to the normal adrenal medulla.

Conclusion: This is the first report, which provides new molecular genetic evidence of association between a somatic IRP1 loss-of-function mutation in PHEO and secondary polycythemia. Patients diagnosed with PHEO/PGL and polycythemia that test negative for genetic mutations in HIF2A, PHD1/2, and VHL, IRP1 could be considered for testing of this gene.

 

Nothing to Disclose: YP, GG, CY, HW, ZA, SDP, ZZ, KP