Primary hyperparathyroidism (PHPT) is a common endocrine disorder characterized by dysregulation of parathyroid hormone release. The large majority of PHPT cases are attributable to sporadic, single-gland parathyroid adenoma, in which MEN1 and CCND1/cyclin D1 are the most well-established drivers of tumorigenesis. Sporadic parathyroid carcinoma, which appears to mostly arise through molecular pathways distinct from those causing benign parathyroid tumors, is rare and is most frequently driven by mutational inactivation of the CDC73 (HRPT2) tumor suppressor gene. Targeted investigation of suspected tumor driver genes, as well as unbiased whole-genome or exome sequencing of small cohorts, have revealed additional novel candidate tumor genes in sporadic parathyroid neoplasia, generally at modest or low mutational frequencies consistent with marked molecular genetic heterogeneity from tumor to tumor. The ability of these additional candidates to participate in the pathogenic process of driving parathyroid tumorigenesis in vivo largely remains to be demonstrated experimentally. This review will summarize the molecular genetic abnormalities identified to date in sporadic PHPT and discuss the strength of evidence for their proposed roles in parathyroid tumor formation.

Hybrid genetic elements, Mud-P and Mud-Q (collectively, Mud-P22s), have been constructed that carry two-thirds of the temperate Salmonella phage P22 genome sandwiched between the ends of transposon Mu. Insertions of these elements in the Salmonella chromosome generate locked-in P22 prophages that cannot excise. Upon induction (as a consequence of the inactivation of P22 c2 repressor), a locked-in prophage replicates its DNA in situ, resulting in the amplification of neighboring regions of the chromosome and the processive packaging of three contiguous headsful of adjacent DNA in one direction from the P22 packaging site, pac. Phage particles in an induced lysate of a Mud-P22 lysogen contain DNA molecules corresponding to several minutes of chromosomal DNA adjacent to the site of prophage insertion and transduce nearby genetic markers with high efficiencies. Mud-P22 prophages have been introduced into an F' episome by transposition; resident Mud insertions on the Salmonella chromosome may be converted to Mud-P22 insertions by homologous recombination in P22-mediated transductional crosses.

Objective: Primary hyperparathyroidism is most often caused by a sporadic single-gland parathyroid adenoma (PTA), a tumor type for which cyclin D1 is the only known and experimentally validated oncoprotein. However, the molecular origins of its frequent overexpression have remained mostly elusive. In this study, we explored a potential tumorigenic mechanism that could increase cyclin D1 stability through a defect in molecules responsible for its degradation. Methods: We examined two tumor suppressor genes known to modulate cyclin D1 ubiquitination, PRKN and FBX4, for evidence of classic two-hit tumor suppressor inactivation within a cohort of 82 PTA cases. We examined the cohort for intragenic inactivating and splice site mutations by Sanger sequencing and for locus-associated loss of heterozygosity (LOH) by microsatellite analysis. Results: We identified no evidence of bi-allelic tumor suppressor inactivation of PRKN or FBX4 via inactivating mutation or splice site perturbation, neither in combination with nor independent of LOH. Among the 82 cases, we encountered previously documented benign single nucleotide polymorphisms (SNPs) in 35 tumors at frequencies similar to those reported in the germlines of the general population. Eight cases exhibited intragenic LOH at the PRKN locus, in some cases extending to cover at least an additional 1.7Mb of chromosome 6q25-26. FBX4 was not affected by LOH. Conclusion: The absence of evidence for specific bi-allelic inactivation in PRKN and FBX4 in this sizeable cohort suggests that these genes only rarely, if ever, serve as classic driver tumor suppressors responsible for the growth of PTAs.