Endocrine Abstracts

Pseudohypoparathyroidism (PHPT) is a very rare disorder characterised by a lack of response to parathyroid hormone at the level of the proximal tubule. In the absence of the classical features of Albright Osteodystrophy, the diagnosis can be missed. We present two cases of type 1B PHPT. The first case was of a 39 year old man presenting with non-specific abdominal symptoms and was found to have a corrected calcium of 1.89 mmol/ (2.21-2.52 mmol/l) with a paired PTH of 734pg/ml (15-65pg/ml) but normal phosphate and a slightly raised alkaline phosphatase (ALP). Vitamin D level was 17 nmol/l (>50 nmol/l). He had a normal phenotype. He was treated with intravenous calcium and transitioned to oral calcium, Vitamin D and active vitamin D. Coeliac screen was negative. Three months later calcium normalised to 2.24 mmol/l and vitamin D had climbed to 65 nmol/l. PTH level had fallen but remained significantly raised at 334pg/ml. Genetic testing confirmed a diagnosis of pseudohypoparathyroidism Type 1B due to partial loss of the maternal methylation pattern at the GNAS locus. The second case was of a 22 year old man presenting to his GP after experiencing tetany while abroad, necessitating IV calcium replacement. Corrected serum calcium was low at 1.63 mmol/l with a raised serum phosphate of 1.63 mmol/l with normal ALP and vitamin D and a PTH of 308pg/ml. He had a normal phenotype. Genetic testing diagnosed PHPT Type 1B due to loss of the maternal methylation pattern at the GNAS locus. His calcium normalised on oral calcium with 1600 units of Vitamin D daily and 1 mg of one alpha. PTH remained elevated at 138pg/ml. Pseudohypoparathyroidism should be suspected in individuals with hypocalcaemia, raised PTH and hyperphosphatemia especially if the PTH level remains raised despite correction of calcium and vitamin D deficiency.