We report three neonates with transient
hypoparathyroidism with elevated
parathyroid hormone (PTH) levels to clarify further the pathogenesis of late neonatal
hypocalcemia and
calcium homeostasis. Clinical signs were
seizures starting at age of 10 and 11 days. The biochemical features were characterized by transient
hypocalcemia and
hyperphosphatemia due to a high transport maximum of the
phosphate/glomerular filtration rate, despite high PTH levels. All had normal
magnesium and
calcidiol levels (at least 5 micrograms/l) for their age, and this precludes
hypoparathyroidism due to low
magnesium levels and
hyperparathyroidism due to overt
vitamin D deficiency. To diagnose
pseudohypoparathyroidism type I, intravenous human PTH (1-34) infusions were performed; however, they showed brisk responses of plasma and/or urine
cyclic AMP in response to the PTH infusion, but the phosphaturic response to the PTH was sluggish compared to the controls. All three showed an increase in serum
alkaline phosphatase activity, suggesting PTH stimulation of osteoblasts. They were treated initially with
calcium lactate or (1 alpha)-hydroxycalciol/
calcitriol. Their hypoparathyroid condition, however, was transient; they maintained normal serum
calcium and PTH levels without medication before the age of 6 months. The etiology, possibly intracellular signal transduction distal to
cyclic AMP and/or distinct from
adenylate cyclase in the kidney, is developmental and the condition was resolved completely within 6 months of age. We have termed this condition "transient
pseudohypoparathyroidism of the neonate".