Molecular evaluation of a sporadic paraganglioma with concurrent IDH1 and ATRX mutations

Purpose Pheochromocytomas and paragangliomas (PPGLs) are neuroendocrine tumors of neural crest origin. Germline or somatic mutations of numerous genes have been implicated in the pathogenesis of PPGLs, including the isocitrate dehydrogenase 1 ( IDH1 ) gene and alpha thalassemia/mental retardation syndrome X-linked ( ATRX ) gene. Although concurrent IDH1 and ATRX mutations are frequently seen in gliomas, they have never been reported together in PPGLs. The aim of this study was to characterize one paraganglioma with concurrent IDH1 and ATRX mutations identified by whole exome sequencing. Methods Leukocyte and tumor DNA were used for whole exome sequencing and Sanger sequencing. 2-hydroxyglurarate level and the global DNA methylation status in the tumor were measured. ATRX’s cDNA transcripts were analyzed. Tyrosine hydroxylase (TH), HIF1α and ATRX staining, as well as telomere-specific FISH was also performed. Results The presence of a somatic IDH1 (c.394C>T, p.R132C) mutation and a concurrent somatic ATRX splicing mutation (c.4318-2A>G) in the current case was confirmed. Dramatic accumulation of 2-hydroxyglutarate was detected in the paraganglioma without the global DNA hypermethylation, and pseudohypoxia was also activated. Importantly, immunohistochemistry revealed negative TH staining in the tumor and the first exon region of TH gene was hypermethylated resulting in normal plasma metanephrines. The splicing ATRX mutation resulted in two transcripts, causing frameshifts. Immunohistochemistry revealed scarce ATRX staining in the tumor. Alternative lengthening of telomeres (ALT) was detected by FISH. Conclusions This case represents the first concurrence of IDH1 and ATRX mutations in PPGLs. Although relatively rare, a somatic R132C mutation of IDH1 might play a role in a small subset of sporadic PPGLs.