It is difficult to differentiate between parathyroid neoplasia and hyperplasia. In an attempt to elucidate the clonality of uremic parathyroid hyperplasia and the molecular genetic abnormalities accounting for clonal emergence, we analyzed 20 cases of uremic parathyroid hyperplasia. Clonalities were determined using the X-chromosome-linked human androgen receptor (HUMARA) gene and the phosphoglycerate kinase (PGK) gene, and multiple endocrine neoplasia type 1 (MEN1) gene abnormality was analyzed by studying loss of heterozygosity (LOH) in 11q13 and somatic mutations in the MEN1 gene. As a positive control, a case of MEN1 with Zollinger-Ellison syndrome was analyzed simultaneously. Our analysis revealed that a majority (75%) of the uremic parathyroid hyperplasia tissues, including an autograft with recurrent hyperparathyroidism, was of monoclonal origin. Clonality did not correlate with serum carboxyl-terminal parathyroid hormone (C-PTH) level, calcium level, hemodialytic duration, gland weight or pathological features. Neither LOH in 11q13 nor somatic mutation in the MEN1 gene was detected. For the MEN1 case, a germline mutation (W198X) was detected in exon 3. We concluded that a majority of the uremic parathyroid hyperplasia cases was in fact monoclonal neoplasia. MEN1 gene abnormality played a minor role, if any, in the clonal emergence in uremic parathyroid hyperplasia.Key words: Parathyroid -Uremic parathyroid hyperplasia -Clonality -MEN1 gene Uremic parathyroid hyperplasia is characterized by hypersecretion of parathyroid hormone (PTH) and enlargement of more than one gland. Because of these features, uremic parathyroid hyperplasia is traditionally interpreted as reactive hyperplasia of the parenchymal cells.1, 2) Parathyroid tumors may occur in uremic parathyroid hyperplasia but are considered rare. Recently this concept has been challenged by molecular analysis and clinical longterm follow-up. Molecular analysis has demonstrated that some uremic parathyroid hyperplasia specimens are of monoclonal origin and should therefore be interpreted as neoplastic. 3,4) Clinical studies showed that about 3% and 7% of patients receiving a subtotal parathyroidectomy developed recurrent hyperparathyroidism 5 and 7 years later, respectively. A much higher recurrence rate was observed in autografts, with a frequency of 10, 20 and 30% occurring 3, 5 and 7 years, respectively, after total parathyroidectomy and autotransplantation.
5)In these cases, pathological observation of the autografts often revealed a distinct nodular proliferation of the parenchymal cells with larger and more irregular nuclei. Occasionally, apparent mitotic activity and nuclear pleomorphism were noted. A striking finding by Klempa et al. was the presence of small nests of parathyroid tissue next to or at some distance from the autografts. 6) These observations and evidence are suggestive of a neoplastic nature of uremic parathyroid hyperplasia. However, little is known about the molecular abnormalities accounting for this neoplastic proliferation. In...