ESPE Abstracts

Background: PHP is a rare heterogeneous genetic disorder causing parathyroid hormone (PTH) resistance. This condition is caused by deficiency of the α subunit of the protein Gs, encoded by GNAS gene. Clinical classification is based on presence or absence of Albright hereditary osteodystrophy (AHO) and multiple or single hormone resistance, to PHP1a/1c and PHP1b respectively.

Objective: To describe the clinical and practical management of a case of PHP1a in a challenging clinical context.

Method: Case review of clinical notes and investigations in 8 year old girl with recent hypothyroidism and severe hypocalcaemia. A previous clinical diagnosis of Beckwith Wiedemann syndrome (BWS) was made in the neonatal period, however genetic analysis was negative. At 6 years she was referred to endocrinology services with new onset hypothyroidism.

Results: Severe hypocalcaemia calcium 1.63 mmol/l (RR 2.1–2.62), high PTH 613 ng/l (RR 15–65), and high phosphate 3.10 mmol/l (RR 1.0–1.8), were found, with normal renal function, ultrasound and urinary calcium 0.04 mmol/l. She was commenced on calcium and vitamin D supplements; however the PTH (319 ng/l) remained elevated. Clinical and radiological features were consistent with AHO, PTH resistance with coexisting TSH resistance made the diagnosis of BWS doubtful and PHP1a was considered. The introduction of calcium supplementation generated painful subcutaneous calcinosis in her feet. Daily activities were restricted due to severe pain. She improved only when calcium supplements were stopped and 1,25-dihydroxyvitamin D (One Alpha 25 ng/kg per day) was started. Analgesia and orthotics were an essential part of management. GNAS1 gene and methylation (imprinting defect in PHP1b) defects were negative.

Conclusion: When making a new diagnosis of PHP1a, excess calcium supplementation should be avoided, with a goal to maintain calcium in the low normal range and focus on careful 1,25-dihydroxyvitamin D dose adjustment. Aiming to minimize bone demineralisation and optimize normal PO4, PTH thereby avoiding excessive calcium deposition.