Co-existence of glucagonoma with recurrent insulinoma in a patient with multiple endocrine neoplasia-type 1 (MEN-1)

A novel likely pathogenetic variant p.(Cys235Arg) of the MEN1 gene in multiple endocrine neoplasia type 1 with multifocal glucagonomas

PURPOSE

Multiple endocrine neoplasia type 1 (MEN1) is a hereditary endocrine syndrome caused by pathogenic variants in MEN1 tumor suppressor gene. Diagnosis is commonly based on clinical criteria and confirmed by genetic testing. The objective of the present study was to report on a MEN1 case characterized by multiple pancreatic glucagonomas, with particular concern on the possible predisposing genetic defects.

METHODS

While conducting an extensive review of the most recent scientific evidence on the unusual glucagonoma familial forms, we analyzed the MEN1 gene in a 35-year-old female with MEN1, as well as her son and daughter, using Sanger and next-generation sequencing (NGS) approaches. We additionally explored the functional and structural consequences of the identified variant using in silico analyses.

RESULTS

NGS did not show any known pathogenic variant in the tested regions. However, a new non-conservative variant in exon 4 of MEN1 gene was found in heterozygosity in the patient and in her daughter, resulting in an amino acid substitution from hydrophobic cysteine to hydrophilic arginine at c.703T > C, p.(Cys235Arg). This variant is absent from populations databases and was never reported in full papers: its characteristics, together with the high specificity of the patient's clinical phenotype, pointed toward a possible causative role.

CONCLUSION

Our findings confirm the need for careful genetic analysis of patients with MEN1 and establish a likely pathogenic role for the new p.(Cys235Arg) variant, at least in the rare subset of MEN1 associated with glucagonomas.

Conditional deletion of Men1 in the pancreatic β-cell leads to glucagon-expressing tumor development

The tumor suppressor menin is recognized as a key regulator of β-cell proliferation. To induce tumorigenesis within the pancreatic β-cells, floxed alleles of Men1 were selectively ablated using Cre-recombinase driven by the insulin promoter. Despite the β-cell specificity of the RipCre, glucagon-expressing tumors as well as insulinomas developed in old mutant mice. These glucagon-expressing tumor cells were menin deficient and expressed the mature α-cell-specific transcription factors Brain-specific homeobox POU domain protein 4 (Brn4) and v-maf musculoaponeurotic fibrosarcoma oncogene family, protein B (MafB). Moreover, the inactivation of β-cell-specific transcription factors was observed in mutant β-cells. Our work shows that Men1 ablation in the pancreatic β-cells leads to the inactivation of specific transcription factors, resulting in glucagon-expressing tumor development, which sheds light on the mechanisms of islet tumorigenesis.