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Objective We previously described a family in which predisposition to pheochromocytoma (PCC) segregates with a germline heterozygous KIF1B nucleotide variant (c.4442G>A, p.Ser1481Asn) in three generations. During the clinical follow-up, one proband’s brother, negative for the KIF1B nucleotide variant, developed a bilateral PCC at 31 years. This prompted us to reconsider the genetic analysis. Design and methods Germline DNA was analyzed by next-generation sequencing (NGS) using a multi-gene panel plus MLPA or by whole exome sequencing (WES). Tumor-derived DNA was analyzed by SnapShot, Sanger sequencing or NGS to identify loss-of-heterozygosity (LOH) or additional somatic mutations. Results A germline heterozygous variant of unknown significance in MAX (c.145T>C, p.Ser49Pro) was identified in the proband’s brother. Loss of the wild-type MAX allele occurred in his PCCs thus demonstrating that this variant was responsible for the bilateral PCC in this patient. The proband and her affected grandfather also carried the MAX variant but no second hit could be found at the somatic level. No other pathogenic mutations were detected in 36 genes predisposing to familial PCC/PGL or familial cancers by WES of the proband germline. Germline variants detected in other genes, TFAP2E and TMEM214, may contribute to the multiple tumors of the proband. Conclusion In this family, the heritability of PCC is linked to the MAX germline variant and not to the KIF1B germline variant which, however, may have contributed to the occurrence of neuroblastoma (NB) in the proband.

The identification of Von Hippel-Lindau (VHL) mosaic mutations by conventional Sanger sequencing requires a labour-intensive enrichment step, thus explaining that mosaicism occurrence is underestimated in patients. Nowadays, it is possible to detect mutation in cell sub-populations by next-generation sequencing (NGS). Here, we described a diagnosis strategy using NGS with high coverage in a series of eight patients who were negative for a VHL abnormality by Sanger sequencing and deletion search. In two patients, a mosaic mutation in VHL was detected by NGS. One patient with a 5.7% mutated allele frequency had a severe phenotype and an early disease onset. In conclusion, clinical NGS in an hospital molecular oncogenetics laboratory is an efficient tool to identify VHL mosaic mutation. Its use may improve patient monitoring and genetic counseling.

International audience; MUC5B, mapped clustered with MUC6, MUC2, and MUC5AC to chromosome 11p15.5, is a human mucin gene of which the genomic organization is being elucidated. We have recently published the sequence and the peptide organization of its huge central exon, 10,713 base pairs (bp) in length. We present here the genomic organization of its 3' region, which encompasses 10,690 bp. The genomic sequence has been completely determined. The 3' region of MUC5B is composed of 18 exons ranging in size from 32 to 781 bp, contrasting thus with the very large central exon. The sizes of the 18 introns range from 114 to 1118 bp. Some repetitive sequences were identified in four introns. The peptide deduced from the sequence of the 18 exons consists of an 808-amino acid peptide. This carboxyl-terminal region exhibits extensive sequence similarity to MUC2, MUC5AC, and von Willebrand factor, particularly the number and the positions of the cysteine residues, suggesting that this domain may be derived from a common ancestral gene. The presence in these components of a cystine knot also found in growth factors such as transforming growth factor-beta is of particular interest. Moreover, one part of this peptide is identical to the 196-amino acid sequence deduced from the cDNA clone pSM2-1, which codes for a part of the high molecular weight mucin MG1 isolated from human sublingual gland. Considering the expression pattern of MUC5B and the origin of MG1, we can thus conclude that MUC5B encodes MG1.