Differential Diagnosis for CASR Gene Analysis to R/O FHH vs PHPT
Single Most Likely Diagnosis
- Familial Hypocalciuric Hypercalcemia (FHH): This condition is caused by mutations in the CASR gene, leading to altered calcium sensing and subsequent hypercalcemia with hypocalciuria. The CASR gene analysis is a direct test for this condition, making it the most likely diagnosis.
Other Likely Diagnoses
- Primary Hyperparathyroidism (PHPT): While PHPT is a common cause of hypercalcemia, the CASR gene analysis is specifically used to differentiate FHH from PHPT. However, some cases of PHPT may have similar clinical presentations, making it an important consideration.
- Neonatal Severe Primary Hyperparathyroidism (NSHPT): This is a rare but severe form of PHPT that can be caused by mutations in the CASR gene. Although less common, it is an important diagnosis to consider, especially in neonates.
Do Not Miss Diagnoses
- Lithium-Induced Hypercalcemia: Lithium therapy can mimic FHH by causing hypercalcemia and hypocalciuria. Missing this diagnosis could lead to unnecessary genetic testing and delayed treatment of lithium toxicity.
- Vitamin D Intoxication: Excessive vitamin D intake can cause hypercalcemia, which may be misattributed to FHH or PHPT. Failing to recognize vitamin D intoxication could result in delayed treatment and prolonged hypercalcemia.
Rare Diagnoses
- Bartter Syndrome: This rare genetic disorder affects renal calcium and magnesium handling, leading to hypocalcemia, not hypercalcemia. However, some variants may present with atypical features, making it a rare but possible consideration.
- Autoimmune Hypocalciuric Hypercalcemia: This is a rare condition characterized by autoantibodies against the CASR, leading to hypercalcemia and hypocalciuria. Although rare, it is an important diagnosis to consider in patients with unexplained hypercalcemia and hypocalciuria.