Functional and in silico assessment of MAX variants of unknown significance.

UNLABELLED: The presence of germline mutations affecting the MYC-associated protein X (MAX) gene has recently been identified as one of the now 11 major genetic predisposition factors for the development of hereditary pheochromocytoma and/or paraganglioma. Little is known regarding how missense variants of unknown significance (VUS) in MAX affect its pivotal role in the regulation of the MYC/MAX/MXD axis. In the present study, we propose a consensus computational prediction based on five "state-of-the-art" algorithms. We also describe a PC12-based functional assay to assess the effects that 12 MAX VUS may have on MYC's E-box transcriptional activation. For all but two of these 12 VUS, the functional assay and the consensus computational prediction gave consistent results; we classified seven variants as pathogenic and three as nonpathogenic. The introduction of wild-type MAX cDNA into PC12 cells significantly decreased MYC's ability to bind to canonical E-boxes, while pathogenic MAX proteins were not able to fully repress MYC activity. Further clinical and molecular evaluation of variant carriers corroborated the results obtained with our functional assessment. In the absence of clear heritability, clinical information, and molecular data, consensus computational predictions and functional models are able to correctly classify VUS affecting MAX. KEY MESSAGES: A functional assay assesses the effects of MAX VUS over MYC transcriptional activity. A consensus computational prediction and the functional assay show high concordance. Variant carriers' clinical and molecular data support the functional assessment.

Usefulness of negative and weak-diffuse pattern of SDHB immunostaining in assessment of SDH mutations in paragangliomas and pheochromocytomas.

This is a confirmatory study about usefulness of SDHB and SDHA immunostaining in assessment of SDH mutations in paragangliomas and pheochromocytomas. Paraganglioma/pheochromocytoma syndrome (PGL/PCC syndrome) consists of different entities, associated with germline mutations in five different genes: SDHD, SDHAF2, SDHC, SDHA and SDHB. It has been suggested that negative immunostaining of SDHB can be taken as an indicator of the presence of a mutation in one of the five SDH genes. We have performed SDHB and SDHA immunohistochemical staining in a series of paragangliomas and pheochromocytomas from 64 patients. The patients had been previously checked for mutations in SDHD, SDHC and SDHB, but also for mutation in RET and VHL. All 14 patients with SDH mutations (9 with SDHB and 5 with SDHD mutations) exhibited negative or weak-diffuse SDHB staining pattern in tumour tissue, whereas cells of the 23 RET mutated and 8 VHL mutated tumours showed a positive SDHB immunostaining. Sixteen of the patients that did not exhibit a mutation in any gene showed positive SDHB immunostaining in tumour tissue, while only three of the patients without mutation exhibited negative staining. All patients exhibited positive pattern of SDHA immunostaining. The results confirm the value of SDHB immunohistochemical status in assessment of germline mutations in PGL/PCC syndrome.