Identification of somatic mutations in parathyroid tumors using whole-exome sequencing

Abstract

Context: The underlying molecular alterations causing sporadic parathyroid adenomas that drive primary hyperparathyroidism have not been thoroughly defined.

Objective: The aim of the study was to investigate the occurrence of somatic mutations driving tumor formation and progression in sporadic parathyroid adenoma using whole-exome sequencing.

Design: Eight matched tumor-constitutional DNA pairs from patients with sporadic parathyroid adenomas underwent whole-exome capture and high-throughput sequencing. Selected genes were analyzed for mutations in an additional 185 parathyroid adenomas.

Results: Four of eight tumors displayed a frame shift deletion or nonsense mutation in MEN1, which was accompanied by loss of heterozygosity of the remaining wild-type allele. No other mutated genes were shared among the eight tumors. One tumor harbored a Y641N mutation of the histone methyltransferase EZH2 gene, previously linked to myeloid and lymphoid malignancy formation. Targeted sequencing in the additional 185 parathyroid adenomas revealed a high rate of MEN1 mutations (35%). Furthermore, this targeted sequencing identified an additional parathyroid adenoma that contained the identical, somatic EZH2 mutation that was found by exome sequencing.

Conclusion: This study confirms the frequent role of the loss of heterozygosity of chromosome 11 and MEN1 gene alterations in sporadic parathyroid adenomas and implicates a previously unassociated methyltransferase gene, EZH2, in endocrine tumorigenesis.

Fig. 1.

Somatic mutations in EZH2. A, Sequences of constitutional genomic DNA, tumor genomic DNA, and tumor cDNA of EZH2 codons 640–642 in PTH122 of the discovery cohort. B, Sequences of constitutional genomic DNA, tumor genomic DNA, and tumor cDNA of EZH2 codons 640–642 in sample 413 from the large-scale EZH2 SET domain screen. Sequences from the forward direction are shown on the top row and the reverse direction are shown below.

Fig. 2.

Results of the MEN1 mutation screen. Mutation types per base of exon are displayed across exons 2–10 for all 193 tumors. The table displays the total mutational breakdown across all exons compared with the findings from previous studies. FS indels and IF indels represent frame shift and in-frame insertions or deletions, respectively.