Italiano et al. BMC Cancer 2012, 12:408 http://www.biomedcentral.com/1471-2407/12/408 By performing western blotting, we identified a loss of SDHA protein expression in the two mutated cases whereas expression was retained in the non-mutated cases. This result was expected in the tumor with the p. Arg31X mutation because this mutation leads to a trun- cated SDHA protein. Although the p.D38V missense mutation does not lead to a truncated protein, the SDHA expression was significantly decreased by IHC and not detected by Western blot. This result can be explained by a conformational change of the mutated SDHA protein compromising the antigenic epitope for the antibody. Another explanation is that the p.D38V mutation leads to SDHA protein instability. As indicated above, since only the hot spot exons 9 and 13 of SDHA gene were investigated in this case, we cannot exclude the possibility of a germline mutation in a different exon, in keeping with a ‘two-hit’ mechanism of loss of func- tion, implicated in most other SDH-deficient neoplasias. Further investigations are needed to address this point. The persistent expression of SDHA protein in SDHA non-mutated GIST is in accordance with previous studies which showed consistent SDHA protein expression in SDHB-, and SDHD-mutated paraganglioma [25,36]. How- ever, since we have sequenced only exons 2, 9, 13, we can- not exclude the unlikely possibility of a SDHA mutation even in cases showing SDHA protein expression. Previous studies demonstrated that SDHB-, SDHC-, and SDHD- related paragangliomas and GIST all show loss of SDHB immunohistochemical expression [11,36]. It was suggested that absence of functional SDHC or SDHD leads to im- pairment of complex II formation and degradation of SDHB. Our results, showing absence of SDHB expression in SDHA-mutated GIST, are in accordance with this ex- planation. In contrast, whereas SDHB expression was not detected in all WT GIST included in our series, all these tumors (except the two with a mutation of the SDHA gene) displayed expression of SDHA. These findings sug- gest that the SDHB protein is degraded when the succin- ate dehydrogenase complex II is disrupted, whereas the SDHA protein remains intact. By pooling our results with those of previous studies [11,16,17,37], it appears that the majority of mutations of genes encoding subunits of the SDH complex II iden- tified in apparently sporadic KIT and PDGFRA WT GIST occurred in young adults (9 out of 13 patients). However, the majority of sporadic or syndromic KIT and PDGFRA WT GIST, occurring in the pediatric or young adult setting, display loss of SDHB protein [10], suggest- ing that defects in cellular respiration is a crucial event even in cases without mutation of the succinate de- hydrogenase complex II. Therefore, further investigation are needed to identify the mechanism involved in the al- teration of the succinate dehydrogenase complex II func- tion in cases without mutation of SDHA, -B, -C or -D. Page 6 of 7 Conclusion In conclusion, this study provides additional evidence that SDHA is another important gene involved in the tumorigenesis of a subset of GISTs lacking KIT or PDGFRA mutation. Although the number of identified mutation carriers is still low, current observations sug- gest that mutations of the succinate dehydrogenase com- plex II are more particularly associated with KIT and PDGFRA WT GIST occurring in young adults, outside the Carney’s triad trait. Although pediatric GIST consist- ently display alterations of SDHB protein expression, further molecular studies are needed to identify the cru- cial genetic events involved in their tumorigenesis. Gen- etic screening for SDHB, C and D germline mutations is recommended for patients with paraganglioma/pheo- chromocytoma and SDH deficient GISTs. At the time of this writing, it remains uncertain whether patients with SDHA-deficient GIST are also at increased risk for the tumors associated with SDHx germline mutation. The penetrance of SHDA mutations is also unknown. There- fore, further investigations are needed to clarify the clinical significance of a SDHA germline mutation and its impact in terms of genetic counseling. Competing interests The authors declare that they do not have any competing interests. Authors’ contributions AI, CLC, and YSS performed the molecular genetic analysis. AI and CRA wrote the manuscript. SS, PB, RPD and MPL participated in project design and provided clinical input. NS run the bioinformatic data analysis. All authors read and approved the final manuscript. Acknowledgements We thank Agnes Viale and the Genomic Core Lab for excellent technical support, Nicole Moraco for providing follow-up information and Milagros Soto for editorial assistance. Author details 1Departments of Pathology, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10065, USA. 2Institute Bergonie, Bordeaux, France. 3Departments of Surgery, Memorial Sloan-Kettering Cancer Center, New York, NY, USA. 4Developmental Biology, Sloan-Kettering Institute, New York, NY, USA. 5Bioinformatics, Memorial Sloan-Kettering Cancer Center, New York, NY, USA. 6Visiting Research Fellow from the Bergonie Institute, Bordeaux, France. Received: 2 April 2012 Accepted: 6 September 2012 Published: 14 September 2012 References 1. 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