A Novel RET D898Y Germline Mutation in a Patient with Pheochromocytoma


Introduction

Pheochromocytomas (PCCs) and paragangliomas (PGLs) are chromaffin cell origin neuroendocrine tumors. PCCs arise from the adrenal medulla and produce catecholamines, whereas paragangliomas occur in the thoracoabdominal sympathetic or parasympathetic ganglia and may, or may not, be associated with catecholamine secretion.In the present study, a novel germline RET gene mutation (c.2692G>T, p.Asp898Tyr) of unknown significance was identified in a patient with PCC and her family members at the Seoul National University Hospital, South Korea. 

Case Report

In November 2012, a 49-year-old Korean woman was referred to the Department of Endocrine Surgery due to a right adrenal mass, identified by abdominal sonography during a routine healthcare checkup. She had been suffering from headache, tachycardia, palpitations, and cold sweats for 5 years but had not previously undergone adrenal disease related diagnostic tests. Her mother and two sisters had a history of thyroidectomy as treatment for papillary thyroid cancer. 

Diagnosis

Twenty-four-hour urine collection revealed elevated vanillyl mandelic acid (VMA; 11.7 mg/day, reference: 2–7 mg/day), metanephrine (1625.6 μg/day, reference: 52–341 μg/day), normetanephrine (5459.5 μg/day, reference: 88–444 μg/day), epinephrine (256.4 μg/day, reference: 0.20 μg/day), and norepinephrine (153.2 μg/day, reference: 15–80 μg/day).

An abdominal computed tomography (CT) scan revealed a heterogeneous right adrenal mass of approximately 4.7 × 3.5 cm. Metaiodobenzylguanidine scintigraphy and single-photon emission CT showed increased uptake in the right adrenal gland

Treatment

The patient underwent right adrenalectomy using the posterior retroperitoneoscopic approach. The final pathologic diagnosis was a PCC with a size of 6.0 × 4.0 × 3.0 cm and a high risk of malignancy with a “PCC of the adrenal gland scaled score” of 13.During the 65-month follow-up after adrenalectomy, the levels of urine VMA, catecholamine, serum calcitonin, calcium, carcinoembryonic antigen, and parathyroid hormone remained within normal ranges. There was no evidence of malignant thyroid nodules on neck ultrasound examination. Genetic counseling was performed by a specialist nurse. Due to the family history of thyroid cancer, we suggested germline mutation screening of the RET gene to the patient and her family members. The index patient and her two sons, two younger brothers, one younger sister, and mother agreed to the germline mutation test and provided informed consent. The informed consent statement contained a statement concerning the sharing of results as follows: “The research, which was conducted for your information or human tissue samples, can be shared with other researchers through congress. We can publish the results so that other interested people can learn from this study.”

Discussion

Mutation AnalysisGenomic DNA was extracted from peripheral blood samples from the index patient and her family members. For the index patient, mutation testing included RET gene exons 8, 10, 11, 13, 14, 15, and 16 and their flanking regions using PCR and direct sequencing of DNA. For the family members, direct sequencing was performed only for RET exon 15. The GenBank reference sequence used to analyze data generated by direct sequencing was NM_020975.4. The Ensembl VEP (variant effect predictor, http://www.ensembl.org/info/docs/tools/vep/index.html) program was used to predict the biological effect of single nucleotide variants. To predict the impact of amino acid changes on protein structure and function, we used the SIFT (http://sift.jcvi.org/) and PolyPhen (http://genetics.bwh.harvard.edu/pph2/bgi.shtml) prediction tools. The ExAC database (http://exac.broadinstitute.org/) was used to identify the frequency of novel single nucleotide variants in the general population. To evaluate the clinical significance of previously reported RET gene variants, we exploited the dbSNP (https://www.ncbi.nlm.nih.gov/SNP/) and ClinVar (https://www.ncbi.nlm.nih.gov/clinvar/) databases.A germline mutation in the RET gene was identified in the index patient, her two sons, and her older sister. It was not identified in the mother or two younger brothers and one sister of the patient. Sanger sequencing revealed that the RET gene mutation was a c.2692G>T substitution (chromosome 10:43120165, reference sequence, GRCh38.p5). VEP analysis indicated that the mutation alters a GAT codon to TAT, resulting in a change in codon 898 (p.D898).. The score of the change according to the SIFT tool was 0, indicating that it is predicted to be “deleterious.” The PolyPhen score was 1, indicating that it is predicted as “probably damaging.” The frequency of the mutant allele in the population, estimated using the ExAC database, was , indicating that this is an extremely rare allele. Her sister and two sons, who also carried the mutation, did not develop any tumors during the 65-month surveillance period, although her sister had a history of thyroid cancer 

Keywords

RET D898Y Germline Mutation, Pheochromocytoma

Author : Jin Wook Yi et.al.