SUN-403 Apparent Mineralocorticoid Excess (AME): Challenges in the Newborn Period

Abstract Disclosure: S. Patel: None. L. Choleva: None. M. Wilkes: None. C.J. Romero: None. B.C. Shah: None. R. Rapaport: None. J.C. Han: None. M. Yau: None. Classic apparent mineralocorticoid excess (AME) is a rare form of low renin hypertension. It is caused by pathogenic variants in the HSD11B2 gene that codes for the enzyme 11 beta-hydroxysteroid dehydrogenase type 2, which converts cortisol to cortisone. As the excess cortisol has an affinity for the mineralocorticoid receptor, it can cause severe hypertension and hypokalemia. Case reports describe the earliest diagnosis and treatment in infancy, as young as 7 months old. We describe an infant diagnosed with AME at 2 weeks of life and the subsequent management. Pediatric Endocrinology was consulted at 28 hours of life for a male infant born at 27 weeks gestation (GA) to a mother with AME. His mother is homozygous for the Δ299 variant, c.895_897del (p.Tyr299del), in HSD11B2, and his father is a carrier of the same variant. The parents are 1st cousins. During pregnancy, the mother was switched from spironolactone to eplerenone to avoid teratogenic effects. The pregnancy was complicated by intrauterine growth restriction and severe maternal hypertension requiring labetalol and nifedipine. We recommended frequent monitoring of the infant’s blood pressure (BP) every 6 hours, daily electrolytes, and genetic testing. The birth weight was 0.47 kg (1.05% for GA), length 34 cm (15.5% for GA), and head circumference 20.5 cm (0.01% for GA). On initial labs, Na+ was 135 meQ/L, K+ 3.3 meQ/L, HCO3- 24.6 meQ/L, aldosterone <1.0 ng/dL, renin 6.2 ng/mg/hr, and urine free cortisol to cortisone ratio was elevated at 78:1. Genetic analysis at 2 weeks showed homozygosity for the Δ299 variant, confirming AME. At 5 weeks of life, he was hypertensive to 88/53 mmHg (92%/98%ile for age), and renin downtrended to 3.4 ng/mg/hr. Spironolactone was then started at 1 mg/kg/day. KCl supplementation was added after K+ continued to be <4 meQ/L, but discontinued after K+ increased to 5.2 meQ/L ∼3 months of life. At his most recent follow-up at age 6 months, weight improved to 5.65 kg (11.9% for corrected age), while BP was 111/84 mmHg (99%/99%ile for age) and renin was <0.167 ng/mg/hr. The spironolactone dose was therefore increased to 2 mg/kg/day. To our knowledge, this patient is the youngest diagnosed and treated for AME. Patients with AME have been previously reported to present at the earliest in later infancy. However, at 5 weeks of age, our patient was hypertensive and hypokalemic, with a downward trend in renin that guided us to initiate spironolactone. By starting spironolactone at this age, we desire to mitigate the risks of longstanding hypertension. BP and electrolytes are not routinely checked in infants; perhaps in newborns with concerns for AME, they should be monitored to avoid missing diagnoses or indications for treatment. As there are no guidelines on caring for AME in the newborn period, by reporting this case we aim to contribute potential management strategies to the literature. Presentation: Sunday, July 13, 2025