SAT186 Young Patient With Primary Hyperparathyroidism And Mutation Of CDKN1B Gene MEN 4 Variant

Disclosure: J.J. Faria Briceno: None. S.S. Jande: None. T. Lairmore: None. R.R. Yatavelli: None. Background: Parathyroid adenomas are the most common cause of primary hyperparathyroidism (PHPT)accounting for 80-85% of the cases. PHPT most commonly manifests between 50-60 years of age and when it presents at younger age, it can be associated with inherited genetic conditions like multiple endocrine neoplasia or Hyperparathyroid Jaw tumor syndrome. Clinical Case: A 34-year-old male without significant past medical history was noted to have elevated serum calcium on routine lab work and was advised to promptly go to the emergency room for further evaluation. In the ED, the patient’s corrected calcium was 13.8 mg/dL (normal range 8.7 - 10.5 mg/dL), ionized calcium elevated at 1.77 mmol/L (normal range 0.90 - 1.20 mmol/L), PTH was 786.2 pg/mL (normal range 9 - 77 pg/mL). The patient denied any history of fractures, kidney stones or bone pain. Patient was treated medically with IV fluids and calcium lowering agents. Given the elevated PTH, ultrasonography of the neck was done which revealed an oval, hypoechoic lesion measuring 1.2 x 2.25 cm with increased vascular flow posterior to the right thyroid lobe consistent with parathyroid adenoma. Parathyroidectomy was performed with excision of right inferior parathyroid adenoma measuring 2.7 x 1.2 x 0.6 cm (1.25 grams). The preoperative PTH level was 997.7 pg/mL, which rapidly improved 20 minutes post tumor excision to 75.9 pg/mL, a 90% fall in PTH level suggestive of successful tumor excision. The patient’s post-operative period was uneventful. Considering the very young age of presentation; hyperparathyroidism genetic panel was obtained to rule out any inherited conditions like MEN1 or Hyperparathyroid Jaw tumor syndrome. Genetic testing revealed a germline missense mutation in CKDN1B (variant c.287C &gt, heterozygous) and classified as Variant of Uncertain significance). Mutations in the cyclic dependence kinase inhibitor 1B (CDKN1B) have been identified as the culprit for tumor growth seen in multiple endocrine neoplasia 4. MEN4 is a rare autosomal dominant endocrine tumor syndrome characterized by hyperparathyroidism and pituitary adenomas. The variant described in our patient has classically not been associated with other tumors and the available evidence is currently insufficient to determine the role of this variant in disease and hence classified as Variant of Uncertain Significance. Conclusion: Genetic testing should be considered in patients with primary hyperparathyroidism who present at very young age or have multiglandular disease. Our patient does not have any other classic features of MEN 4 and as the genetic mutation is classified as Variant of Uncertain Significance, patient would be monitored clinically, and caution exercised before using this result to inform clinical management decisions. Presentation: Saturday, June 17, 2023