Genetic alterations in primary and secondary hyperparathyroidism

Molecular pathways associated with transcriptional alterations in hyperparathyroidism

Hyperparathyroidism is characterized by the oversecretion of parathyroid hormone biochemically and increased cell proliferation histologically. Primary and secondary hyperparathyroidism exhibit distinct pathophysiology but share certain common microscopic features. The present study performed the first genome-wide expression analysis directly comparing the expression profile of primary and secondary hyperparathyroidism. Microarray gene expression analyses were performed in parathyroid tissues from 2 primary hyperparathyroidism patients and 3 secondary hyperparathyroidism patients. Unsupervised hierarchical clustering analysis identified two natural subgroups containing different types of hyperparathyroidism. Combined with additional data extracted from a publicly available database, a meta-signature was constructed to represent an intersection of two sets of differential expression profile. Multiple pathways were identified that are aberrantly regulated in hyperparathyroidism. In primary hyperparathyroidism, dysregulated pathways included cell adhesion molecules, peroxisome proliferator-activated receptor signaling pathway, and neuroactive ligand-receptor interaction. Pathways implicated in secondary hyperparathyroidism included tryptophan metabolism, tight junctions, renin-angiotensin system, steroid hormone biosynthesis, and O-glycan biosynthesis. The present study demonstrates that different pathophysiology is associated with differential gene profiling in hyperparathyroidism. Several pathways are involved in parathyroid dysregulation and may be future targets for therapeutic intervention.

Hyperparathyroidism and subsequent cancer risk in Denmark

BACKGROUND

There is increasing evidence that hyperparathyroidism (HPT), a condition that leads to elevated serum calcium levels, is associated with endocrine and other malignancies, suggesting a possible causal link between HPT and carcinoma.

METHODS

To investigate the relation of HPT to subsequent cancer risk, the authors conducted a record-linkage study among 2425 patients who were diagnosed with HPT in Danish hospitals. Patients were identified in hospital discharge records, and records were then linked with the Danish National Cancer Registry for the years 1977-1993 to identify cancer incidence. To estimate cancer risk, standardized incidence ratios (SIRs) were computed.

RESULTS

After excluding patients who were diagnosed in the first year of follow-up, a total of 219 malignancies were observed, resulting in an SIR of 1.25 (95% confidence interval [95%CI], 1.1-1.4). Cancer risk among women was higher than among men. Among those with primary (idiopathic) HPT, hematopoetic malignancies were elevated significantly (SIR, 1.88; 95%CI, 1.0-3.2; based on 13 patients), with the excess derived primarily from 4 observed patients with multiple myeloma. Patients with secondary HPT had an insignificantly increased risk of overall cancers. Patients who were diagnosed with other or unspecified types of HPT had significant increases in carcinoma of the urinary tract (SIR, 2.71; 95%CI, 1.2-5.3; based on 8 patients) and carcinoma of the thyroid gland (SIR, 21.19; 95%CI, 4.3-61.9; based on 3 patients).

CONCLUSIONS

Future studies should monitor whether specific endocrine alterations associated with HPT may affect the long-term risk of hematopoetic, thyroid, and urinary tract carcinomas.

Overexpression and genetic abnormality of p53 in parathyroid adenomas

To study the significance of p53 abnormality in parathyroid tumors, 32 parathyroid adenomas and 22 hyperplastic glands from 14 cases of secondary hyperparathyroidism were analysed using immunohistochemistry, polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), single-strand conformation polymorphism (SSCP) and DNA sequencing. Immunohistochemical study revealed p53 overexpression in four parathyroid adenomas, of which two showed diffuse and one showed focal nuclear pleomorphism. Genetic analysis disclosed allelic loss in one, and a point mutation (R290H) and a polymorphism (L257 L) in another of the two other adenomas with diffuse nuclear pleomorphism. No abnormalities were discovered in the other two adenomas, although one had a R72P polymorphism in exon 4. There was no evidence of malignancy of the four tumors in either clinical or pathological terms. None of the 22 hyperplastic glands showed p53 overexpression. These results demonstrate that p53 abnormality can occur in benign parathyroid adenomas and is more prevalent in those with nuclear pleomorphism than in those without.

Clonal emergence in uremic parathyroid hyperplasia is not related to MEN1 gene abnormality

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.