Independent Genetic Events Associated with the Development of Multiple Parathyroid Tumors in Patients with Primary Hyperparathyroidism

Abstract

Multiple parathyroid tumors, as opposed to hyperplasia, have been reported in a subset of patients with sporadic primary hyperparathyroidism (PHPT). It is not clear whether these multiple tumors are representative of a neoplastic process or whether they merely represent hyperplasia that has affected the parathyroid glands differentially and resulted in asynchronous growth. The molecular genetic techniques of comparative genomic hybridization (CGH), loss of heterozygosity (LOH), and MEN1 mutation analysis were performed on a series of five patients with multiglandular PHPT, each of which had two parathyroid tumors removed. Analysis of these multiple parathyroid tumors from patients with PHPT revealed that independent genetic events were associated with the development of a subset of these tumors. The DNA sequence copy number changes, identified by CGH analyses, either involved different chromosomal regions in the paired glands of a patient (two patients), or those regions implicated in one gland were not changed in a second gland from the same patient (two patients). Each of the three patients exhibiting LOH demonstrated different changes between the paired glands. Where LOH was detected in one gland from a patient, the other gland from the same patient either exhibited no allelic loss or the loss detected was in another region. Each of the three tumors exhibiting LOH at 11q13 was found to contain a somatic MEN1 mutation in the remaining allele, however these mutations were not present in the germline or in the paired gland from the same patient. Although it is possible that a separate series of genetic changes has arisen randomly in two separate glands within the same individual, it seems more likely that the development of these multiple tumors has arisen because of the involvement of other unknown factors. These factors may be genetic [such as the involvement of one or more germline mutations in an unknown low-penetrance gene(s), germline mosaicism or alterations in calcium-sensing receptor gene(s)], epigenetic, physiological, or environmental.