Recurrent Hyperparathyroidism Due to a Novel CDC73 Splice Mutation

Abstract

The recognition of hereditary causes of primary hyperparathyroidism (pHPT) is important because clinical care and surveillance differ significantly between sporadic and hereditary pHPT. In addition, the increasing number of genetic tests poses a challenge to classify mutations as benign or pathogenic. Functional workâ up of variants remains a mainstay to provide evidence for pathogenicity. We describe a 52â yearâ old male patient with recurrent pHPT since age 35 years. Despite several neck surgeries with complete parathyroidectomy, he experienced persistent pHPT, necessitating repeated surgery for a forearm autotransplant, which finally resulted in unmeasurable parathyroid hormone (PTH) levels. Genetic testing revealed a new CDC73 variant (c.238â 8G>A [IVS2â 8G>A]), initially classified as a variant of uncertain significance. Parathyroid tissue from the initial surgeries showed loss of heterozygosity. Using an RTâ PCR approach, we show that the mutation leads to the use of a cryptic splice site in peripheral mononuclear cells. In addition, a minigene approach confirms the use of the cryptic splice site in a heterologous cell system. The novel c.238â 8G>A CDC73 variant activates a cryptic splice site, and the functional data provided justify the classification as a likely pathogenic variant. Our results underscore the importance of functional workâ up for variant classification in the absence of other available data, such as presence in diseaseâ specific databases, other syndromic clinical findings, or family history. In addition, the presented case exemplifies the importance to consider a hereditary condition in young patients with pHPT, particularly those with multiâ gland involvement. © 2017 American Society for Bone and Mineral Research.