Objective: To determine whether familial isolated hyperparathyroidism (FIHP) is a variant of multiple endocrine neoplasia type 1 (MEN1) we analyzed the MEN1 gene in such a kindred.
Design and methods: The study included the 70-year-old proband and nine relatives. Blood was drawn for biochemical evaluation and germline mutation analysis by direct sequencing of the MEN1 gene amplified by PCR. A hyperplastic parathyroid gland obtained from a family member served for a loss of heterozygosity (LOH) study.
Results: Three members from two generations in this kindred were found to have primary hyperparathyroidism, while none had clinical or biochemical evidence of MEN1, MEN2 or hyperparathyroidism--jaw tumor syndrome. Analysis of germline DNA in the proband showed a missense mutation (GGC-->GAC) at codon 305 in exon 7 of the MEN1 gene that predicts an amino acid change from glycine to aspartic acid (G305D). This mutation segregated with primary hyperparathyroidism in the kindred, and, in addition, there were two asymptomatic mutant-gene carriers at relatively advanced ages. In contrast, the mutation was not detected in genomic DNA from five unaffected individuals and from 50 healthy subjects. The LOH study showed a loss of the wild-type allele, which confirmed that a functional defect of the MEN1 gene product, menin, is etiological for FIHP.
Conclusions: FIHP is a genetically heterogeneous disease with a subset linked to MEN1, most likely representing a variant of MEN1. The late onset and the reduced penetrance of disease found in this kindred may be related to the site and the type of mutation, although the precise mechanism involved is unknown at present.