MON-763 - Postpartum Hypocalcemia Revealing Pseudohypoparathyroidism Type 1B Due to an STX16 Mutation

Pseudohypoparathyroidism (PHP) is a rare disorder of parathyroid hormone (PTH) resistance characterized by hypocalcemia, hyperphosphatemia, and elevated PTH levels. Diagnosis may be delayed, particularly in patients lacking phenotypic features of Albright hereditary osteodystrophy (AHO). Physiologic changes during pregnancy and the postpartum period may unmask underlying disorders of calcium metabolism.

This is a case of a 25-year-old female that was referred for evaluation of severe hypocalcemia following twin delivery. During pregnancy, she experienced bilateral hand numbness. On postpartum day one, she developed profound fatigue and altered mental status. Serum calcium was 6.0 mg/dL (reference 8.6–10.3), though she was discharged without treatment. Persistent upper extremity numbness and worsening cognitive symptoms led to repeat evaluation approximately 1 month postpartum, revealing a calcium level of 5.3 mg/dL (reference 8.2–10.2). She was treated with intravenous calcium and discharged on calcium carbonate, calcitriol, and vitamin D. Laboratory evaluation demonstrated hypocalcemia with a markedly elevated intact PTH of 260 pg/mL (reference 15–65), hyperphosphatemia of 6.4 mg/dL (reference 2.5–5.0), normal 25-hydroxyvitamin D level, and normal renal function. She denied nephrolithiasis, polyuria, gastrointestinal symptoms, or classic neuromuscular irritability. She lacked phenotypic features of AHO. Review of prior records revealed hypocalcemia for at least seven years. She was continued on oral calcitriol 0.5 mcg twice daily and oral calcium carbonate 1000 mg daily. ​​Genetic testing identified a pathogenic STX16 mutation, consistent with autosomal dominant pseudohypoparathyroidism type 1B. None of her children were found to have hypocalcemia. On follow-up, the patient experienced significant clinical and biochemical improvement with normalization of serum calcium.

This case illustrates postpartum unmasking of pseudohypoparathyroidism type 1B presenting as a hypocalcemic crisis with neurocognitive symptoms. Recognition of biochemical PTH resistance in the absence of AHO is essential for diagnosis. Genetic confirmation enables accurate classification, counseling, and management, with favorable outcomes when appropriately treated.

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