Molecular Diagnosis and Clinical Characterization of Pseudohypoparathyroidism Type-Ib in a Patient With Mild Albright's Hereditary Osteodystrophy-Like Features, Epileptic Seizures, and Defective Renal Handling of Uric Acid

We describe a patient who presented with epileptic seizures unresponsive to anticonvulsive treatment. Laboratory investigations demonstrated epileptiform seizure activity in the brain but also revealed severe hypocalcemia, hyperphosphatemia, and elevated serum parathyroid hormone. In addition, the patient showed a reduced serum level of 25-[OH]-vitamin D. The diagnosis of pseudohypoparathyroidism type-Ib (PHP-Ib) was made based on these clinical findings and upon identification of a 3-kb deletion within the STX16 locus, a genetic defect frequently associated with autosomal dominant PHP-Ib. This mutation was also present in the patient's unaffected mother and her affected sister. Despite the molecular diagnosis of PHP-Ib, which is characterized by parathyroid hormone resistance in the absence of Albright's hereditary osteodystrophy (AHO), the patient had a round face, slightly short stature, and short fourth metacarpals, which were consistent with mild AHO. The patient and her affected sister, who lacked AHO-like features, showed reduced serum levels of uric acid and increased fractional excretion of uric acid, a finding that was reported only once previously for PHP-Ib. Unlike the previous report, the fractional uric acid excretion and serum uric acid levels returned to normal in our patient and her sister after 3 months of treatment period. These findings underscore several important points with respect to the pathogenesis and clinical presentation of PHP-Ib. Furthermore, the findings in the index case present interesting novel aspects, including a previously undescribed coexistence of the 3-kb STX16 deletion and AHO-like features and a clinical course complicated by concomitant 25-[OH]-vitamin D deficiency, which may have resulted, at least partly, from long-term use of antiepileptic drugs.