A 35-year-old man is found to have hypercalcemia (serum Ca 11.8 mg/dL), elevated PTH, and low urinary calcium excretion. His mother and sister have similar biochemical profiles. Genetic analysis reveals a heterozygous inactivating mutation in the CASR gene. What is the diagnosis?
- A Primary hyperparathyroidism
- B Familial hypocalciuric hypercalcemia ✓
- C MEN type 2A
- D Neonatal severe hyperparathyroidism
Correct answer: B. Familial hypocalciuric hypercalcemia
Explanation
Heterozygous inactivating CASR mutation causes familial hypocalciuric hypercalcemia (FHH), an autosomal dominant condition with mild hypercalcemia, inappropriately normal or mildly elevated PTH, and low urine calcium. It is benign and does not require parathyroidectomy. Neonatal severe hyperparathyroidism requires biallelic inactivation.
Reference: Williams Textbook of Endocrinology, 14th ed.
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