SAT-738 Adult-onset Hypocalcemia Revealing Digeorge Syndrome (22q11.2 Deletion Syndrome): A Rare Case Of Late Diagnosis

Abstract Disclosure: K. Poolpong: None. S. Siriwong: None. T. Raomanachai: None. DiGeorge syndrome (22q11.2 deletion syndrome) is typically diagnosed in childhood due to congenital cardiac anomalies, hypocalcemia, immune deficiency, or craniofacial features. Adult-onset hypocalcemia as the first clinical manifestation remains exceptionally rare. We report a 43-year-old Thai male with no known childhood developmental concerns who presented with acute carpal spasms. Biochemical evaluation revealed hypocalcemia (serum calcium 6.24 mg/dL), low phosphate, and inappropriately normal PTH (23.1 pg/mL), indicating primary hypoparathyroidism. His past medical history included treated thyrotoxicosis. Physical examination revealed positive Chvostek and Trousseau signs, a harsh pansystolic murmur grade 3/6 at the left mid and lower parasternal border, cleft palate with dental loss, and mild bilateral sensorineural hearing loss. ECG showed QTc prolongation (488 ms), and echocardiography confirmed a small perimembranous ventricular septal defect. Genetic testing via FISH confirmed a 22q11.2 microdeletion, establishing the diagnosis of DiGeorge syndrome. He was treated with intravenous calcium followed by oral calcium carbonate and calcitriol, with resolution of symptoms and normalization of serum calcium. This case is noteworthy for the absence of classical phenotypic clues in childhood and the unusually late onset of hypocalcemia as the first clinical trigger. Compared to other adult DiGeorge cases, our patient had no prior seizures, psychobehavioral symptoms, or neonatal hypocalcemia. Instead, the diagnosis was guided by careful clinical examination and interpretation of subtle features such as cleft palate and congenital murmur. To our knowledge, this case represents one of the latest-age first clinical presentations of DiGeorge syndrome, where isolated hypocalcemia initiated diagnosis. This highlights the importance of considering congenital syndromes such as DiGeorge syndrome in adults with unexplained hypoparathyroidism, especially without history of neck surgery or other causes. Recognition of the 22q11.2 deletion changed the patient's management plan, prompting cardiac surveillance, audiologic support, and genetic counseling. This case underscores the pivotal role of thorough physical examination in uncovering subtle syndromic features that might otherwise go unrecognized. Timely diagnosis not only guides appropriate calcium replacement but also prompts lifelong surveillance and anticipatory care across specialties. Although current guidelines do not recommend routine genetic screening in adult hypocalcemia, this case demonstrates how phenotype-driven clinical judgment can guide appropriate testing and reveal overlooked congenital syndromes. Presentation: Saturday, July 12, 2025