Pathogenicity of DNA variants and double mutations in multiple endocrine neoplasia type 2 and von Hippel-Lindau syndrome

Abstract

Context: Cancer genetics is fundamental for preventive medicine, in particular in pheochromocytoma-associated syndromes. Variants in two susceptibility genes, SDHC and RET, were found in a kindred with head and neck paraganglioma. This observation of coincident DNA variants, both reported as pathogenic, in two known susceptibility genes prompted the question of their pathogenic relevance.

Objective: Our objective was to elucidate the pathogenic role of the detected variants and study the prevalence of such variants.

Patients: Patients were registrants from the European-American Pheochromocytoma-Paraganglioma and German von Hippel-Lindau Disease Registries.

Design: Analysis of germline mutation screening results for all pheochromocytoma-paraganglioma susceptibility genes, including RET [multiple endocrine neoplasia type 2 (MEN 2)] and VHL [von Hippel-Lindau disease (VHL)]. Cases in which more than one DNA variant was found were clinically reevaluated, and cosegregation of the disease with the variant was analyzed within the registrants' families. A total of 1000 controls were screened for the presence of detected variants, and in silico analyses were performed.

Results: Three variants were identified, RET p.Tyr791Phe and p.Ser649Leu and VHL p.Pro81Ser. The frequencies of RET p.Ser649Leu (0.07%) and p.Tyr791Phe (0.9%) compared with controls excluded the two variants' role in the etiology of MEN 2 and VHL. None of the carriers of the RET variants who underwent prophylactic thyroidectomy showed medullary thyroid carcinoma. Clinical reinvestigation of 18 variant carriers excluded MEN 2. VHL variant p.Pro81Ser, also previously described as a mutation, did not segregate with the VHL in one family. In silico analyses for these variants predicted unmodified protein function.

Conclusions: RET p.Tyr791Phe and p.Ser649Leu and VHL p.Pro81Ser are definitely not pathogenic mutations for VHL and MEN 2. Misinterpretation results in irreversible clinical consequences.

Figure 1

Pedigrees of the three key case families. A, Pedigree of key case 1; B, pedigree of key case 2; C, pedigree of key case 3. The essential molecular genetic findings for mutations are indicated by underscoring by a solid line and for polymorphisms by a dotted line. The arrow indicates the index case of the family. AR, Angiomatosis retinae; HBL, hemangioblastoma of the central nervous system; HNP, head and neck PGL; PC, pancreas cysts; PHEO, pheochromocytoma; y, age at manifestation for affected cases (filled symbols) and current age for the unaffected (clear symbols). Genotypes are represented for each considered variant on the protein (p.) level. Del, Large deletions. Findings as Arg/Cys in A, subject II.1, show the results for allele 1 and allele 2. IVS1 is intervening sequence (intron) 1, +5 is the fifth intronic nucleotide. Note that in C, the protein81 and IVS1 + 5 findings are shown for only one allele, because the other allele is deleted.