Multiple endocrine neoplasia type 1 (MEN1): clinical heterogeneity in a large family with a nonsense mutation in the MEN1 gene (Trp471Stop)

Abstract

Objective: Familial multiple endocrine neoplasia type 1 (MEN1) is an hereditary dominant trait characterized by tumours of the parathyroids, anterior pituitary and endocrine pancreatic glands, among others. The MEN1 gene has recently been cloned, and MEN1-mutations have been identified in several families as well as in a number of sporadic cases. The aim of this study was to search for mutations in a large MEN1-family in order to define the clinical heterogeneity among mutation-carriers. We also analysed DNA from several tumour tissues in order to test the 'two hit' model for inactivation of the MEN1 gene.

Patients and methods: We searched for mutations in the MEN1-gene in members of a large MEN1-family. A total of 11 affected and 4 healthy at risk individuals were analysed. DNA was obtained and exons 1 to 10 of the MEN1-gene were PCR-amplified and subjected to automated-direct sequencing. In addition, we isolated DNA from parathyroid tumours of two family members, and compared this DNA with that of the normal tissue counterpart to define if the normal copy of the MEN1-gene was deleted.

Results: G to A change at nucleotide 7640 (exon 10) that would convert Trp to Stop at codon 471 was found. This mutation was identified in eleven affected individuals, as well as in four healthy (asymptomatic) family members. These patients showed a wide spectrum of clinical symptoms and ages of presentation. Comparison of normal and tumour DNAs showed the loss of the normal (non-mutated) copy of MEN1 gene in the tumour tissue.

Conclusion: The different ages of disease presentation and the heterogeneity of symptoms among carriers of the Trp471Stop mutation, which would lead to the synthesis of a truncated non-functional protein, suggest that clinical heterogeneity is a characteristic of MEN1 independent of the type of mutation. Finally, the lack of amplification of the normal MEN1-allele on DNA from parathyroid tumours of two family members indicates that MEN1 is a tumour suppressor gene, the second hit that inactivates the normal copy in mutation carriers being a deletion.