High-grade atrioventricular block in a patient with an Albright hereditary osteodystrophy phenotype

Albright hereditary osteodystrophy is a clinical phenotype associated with disorders involving the GNAS (guanine nucleotide-binding protein, alpha stimulating activity polypeptide) gene, with clinical and biochemical expression influenced by parental imprinting. Pseudopseudohypoparathyroidism refers to the Albright hereditary osteodystrophy phenotype occurring without parathyroid hormone resistance or biochemical abnormalities. Cardiac manifestations in this disease spectrum are more commonly described in pseudohypoparathyroidism, where they are usually attributed to hypocalcaemia-related electrophysiological disturbance. We report a man in his 50s with clinical and radiographic features of Albright hereditary osteodystrophy, normal serum calcium, phosphate and parathyroid hormone levels, and a biochemical profile consistent with pseudopseudohypoparathyroidism. He presented with recurrent syncope and was found to have high-grade second-degree atrioventricular block with 2:1 atrioventricular conduction, requiring permanent pacemaker implantation. This case highlights a rare association between Albright hereditary osteodystrophy phenotype and clinically significant atrioventricular conduction disease in the absence of hypocalcaemia. Although the causality cannot be established from a single case, recognition of characteristic skeletal features may help clinicians identify an underlying syndromic diagnosis in patients presenting with otherwise unexplained arrhythmia.