In PHP Type 1A, what is the typical pattern for serum calcium, phosphate, and PTH?

In PHP Type 1A, what is the typical pattern for serum calcium, phosphate, and PTH?

• A. Hypercalcemia, Hypophosphatemia, Low PTH
• B. Hypocalcemia, Hyperphosphatemia, High PTH
• C. Normal calcium, normal phosphate, normal PTH
• D. Hypercalcemia, Hyperphosphatemia, High PTH

Answer: (B)

The pattern reflects end-organ resistance to parathyroid hormone. In pseudohypoparathyroidism type 1A, the kidneys and bones don’t respond properly to PTH because of a signaling defect (often a Gs alpha subunit mutation). As a result, calcium cannot be adequately mobilized or reabsorbed, so calcium levels fall (hypocalcemia). PTH’s normal job includes promoting phosphate excretion by the kidney; with resistance, phosphate isn’t excreted effectively, so phosphate rises (hyperphosphatemia). The parathyroid glands keep secreting PTH in an attempt to correct the low calcium, so PTH levels are high.

The pattern reflects end-organ resistance to parathyroid hormone. In pseudohypoparathyroidism type 1A, the kidneys and bones don’t respond properly to PTH because of a signaling defect (often a Gs alpha subunit mutation). As a result, calcium cannot be adequately mobilized or reabsorbed, so calcium levels fall (hypocalcemia). PTH’s normal job includes promoting phosphate excretion by the kidney; with resistance, phosphate isn’t excreted effectively, so phosphate rises (hyperphosphatemia). The parathyroid glands keep secreting PTH in an attempt to correct the low calcium, so PTH levels are high.