Normocalcemic pseudohypoparathyroidism type 1B complicated by hypokalemia: A case report

Pseudohypoparathyroidism (PHP) is a heterogeneous group of disorders defined by resistance to parathyroid hormone (PTH), typically stemming from GNAS locus abnormalities. This report describes an unusual case of a 32-year-old Han Chinese male with sporadic PHP Type 1B (PHP1B) who presented with paroxysmal numbness and significant hypokalemia. Despite elevated PTH levels, the patient maintained normocalcemia and showed no evidence of globus pallidus calcification on brain imaging. Diagnosis was confirmed using methylation-specific multiplex ligation-dependent probe amplification, which identified characteristic GNAS imprinting defects: a gain of methylation at the NESP55 exon and loss of methylation at the AS, XL, and A/B exons. With a normal copy number, no detectable GNAS mutations, and a negative family history, the case was classified as sporadic PHP1B. This rare presentation highlights the broad phenotypic spectrum of PHP and emphasizes the clinical importance of monitoring diverse electrolyte disturbances, such as hypokalemia, even when calcium levels appear normal.