Pheochromocytomas (PCC) and paragangliomas (PGL) are genetically heterogeneous neural crest-derived neoplasms. Both conditions are characterised by the growth of benign tumours in structures called paraganglia, affecting approximately one in four million people. Despite their benign character, these tumours can be associated with high morbidity and mortality due to mass effect and high amounts of circulating catecholamines. Germline mutations in the VHL, NF1, RET, TMEM127, SDHD, SDHB and SDHC genes have been shown to associate with PCC or PGL.
Recently, germline mutations in myc-associated factor X (MAX) have been shown to be responsible for 1.12% of PCC/PGL patients (Comino-Mendez I. et al. 2011, Nat Genet. 43:663-7; Burnichon N. et al. 2012, Clin Cancer Res. 18:2828-37). MAX is a member of basic helix-loop-helix leucine zipper (bHLHZ) family of transcription factors. Through its ability to form homo- or heterodimers with other family members, like MYC and MXD1 (MAD), MAX is suggested to act as a tumour suppressor gene and to play an important role in cell proliferation, differentiation and apoptosis (for review see Deng CV. 2012, Cell. 149:22-35; Cascon A. and Robledo M. 2012, Cancer Res. 72:3119-24). Mutations in the succinate dehydrogenase (SDH) complex subunit gene SDHA, can lead to PCCs and PGLs with variable penetrance (Burchinon N. et al. 2010, Hum Mol Genet. 19:3011-20). Moreover, bi-allelic SDHA mutations have been shown to cause an early onset neurodegenerative disorder known as Leigh syndrome (Hovarth R. et al. 2006, J Neurol Neurosurg. 77:74-6).
The SDHA gene (15 exons) spans ~38,5 kb of genomic DNA and is located on chromosome 5p15.33. The MAX gene (5 exons) spans ~27 kb of genomic DNA and is located on chromosome 14q23.3.
This P429-B2 SDHA-MAX probemix contains probes for most exons (10 of 15 exons) of SDHA gene and all five exons of MAX gene. This probemix also contains four flanking probes for SDHA and five flanking probes for MAX genes. In addition, 15 reference probes are included in this probemix, detecting different autosomal chromosomal locations. It should be noticed that cancer karyotypes can harbour multiple numerical and structural aberrations, which can complicate interpretation of these reference probes.
This SALSA® MLPA® probemix is designed to detect copy number changes of one or more sequences in the above mentioned genes. Heterozygous deletions of recognition sequences should give a 35-50% reduced relative peak height of the amplification product of that probe. Note that a mutation or polymorphism (e.g. SNP) in the sequence detected by a probe can also cause a reduction in relative peak height, even when not located exactly on the ligation site! In addition, some probe signals are more sensitive to sample purity and small changes in experimental conditions. Therefore, single probe deletions / duplications detected by MLPA should always be confirmed by other methods or by MLPA probemixes with higher resolution in the gene or chromosomal area of interest. Users should always verify the latest scientific literature when interpreting their findings.