Nontruncated amino-terminal parathyroid hormone overproduction in two patients with parathyroid carcinoma: a possible link to HRPT2 gene inactivation

P>Objective Some patients with parathyroid carcinoma present with an over-production of nontruncated amino-terminal (NT-N) parathyroid hormone (PTH), a post-transcriptionally modified form of PTH(1-84). This is usually picked up on an elevated whole (W) PTH (third-generation)/total (T) (second-generation) PTH assay ratio (N > 0 center dot 8). Patients and design Two parathyroid cancer patients with several episodes of hypercalcaemia and multiple surgeries are described. In both patients, W-PTH, T-PTH and circulating PTH molecular forms separated by high-pressure liquid chromatography (HPLC) were measured with the same assays. qPCR was used to study HRPT2 gene mutation. Results The first patient had total calcium of 3 center dot 8 and 3 center dot 22 mmol/l before the fourth and fifth surgeries, and third/second-generation PTH ratios of 2 center dot 95 and 3 center dot 6, respectively. After the fourth surgery, the ratio remained normal for 1 year and increased progressively to 3 center dot 6 over 15 months. This preceded hypercalcaemia by 6 months. The ratio became normal after the fifth surgery. HPLC analysis disclosed an over-expression of NT-N PTH to 82 center dot 2% (N < 10%) relative to hPTH(1-84) before the fifth surgery. A deletion of all the tested exons of the HRPT2 gene was identified. In the second patient, W-PTH/T-PTH ratio was 0 center dot 89 when serum calcium was 3 center dot 3 mmol/l. NT-N PTH was also over-expressed at 51 center dot 9%. An inactivating mutation of the HRPT2 gene was also identified. Conclusions This may suggest that a progressive rise in third/second-generation ratio may have possible clinical utility to monitor parathyroid cancer recurrence. A possible association between NT-N PTH overproduction and HRPT2 gene inactivation is also suggested.