6611 ACTH deficiency due to TBX19 mutation mimics complete adrenal insufficiency in a newborn

Abstract Disclosure: T. Reinehr: None. P.M. Holterhus: None. S.A. Wudy: None. A. Richter-Unruh: None. C. Spratte: None. C. Roll: None. Isolated ACTH deficiency (IAD) is a rare cause of adrenocortical insufficiency. T-box transcription factor 19 (TBX19) mutations are responsible for more than 60% of neonatal cases of IAD. To the best of our knowledge, we present for the first time a newborn with ACTH deficiency due to a TBX19 mutation with almost steroid-free plasma and urine: At day 2 of life, the female newborn (birth weight 3190g, length 52 cm, 40+1 gestational age) was transferred to our neonatal intensive care unit for severe hypoglycemia (12 mg/dl), which responded to intravenous glucose infusion. Surprisingly, the sodium serum concentrations decreased from 140 mmol/l at day 2 of life to 126 mmol/l at day 7 of life. There were no clinical signs of adrenal insufficiency such as vomiting or hypotonia. Treatment with oral sodium-chloride 5.85% was started. Endocrine diagnostic work-up performed at day 8 of life demonstrated normal values of fT4, HGH and IGFBP-3 ruling out pituitary involvement of these axes, while ACTH serum concentrations were markedly decreased (1.5 pg/ml). Liquid- chromatography-mass spectrometry (LC-MS/MS) revealed nearly absent glucocorticoids (17-hydroxyprogesterone <0.12 nmol/l, 11-deoxycortisol <0.08 nmol/l, cortisol <4.2 nmol/l, and cortisone 1.3 nmol/l (norm value [nv]: 17-138 nmol/l)). Androgens were undetectable (testosterone <0.02 nmol/l, androstenedione <0.08 nmol/l). Mineralocorticoids were severely reduced (11-desoxycorticosterone 0.1 nmol/l (nv: 0.2-1.0 nmol/l), corticosterone 0.6 nmol/l (nv: 1-24 nmol/l), aldosterone 0.1 nmol/l (nv: 0.8-2.3 nmol/l)). In urine spot, gas chromatography-mass spectrometry (GC-MS) demonstrated subnormal excretion of C19 and C21 steroids including fetal zone steroids. Serum and urine measurements were interpreted by the labs as a typical finding similar to StAR defect. The genetic analyses revealed a normal female karyotype (46,XX) and ruled out CYP11A1 and StAR, mutations but demonstrated a homozygous missense mutation in TBX19 (c.172A>G, p.(Thr58Ala)). After 3 months of life under treatment with hydrocortisone (10mg/m² divided in 3 doses) and fludrocortisone (0.05 mg divided in 2 doses), cortisol was normal (320 nmol/l) and DHEAS was undetectable (<3 nmol/l). While androgens were in normal range (testosterone 2.6 nmol/l, androstenedione 0.28 nmol/l), 11-deoxycorticosterone was normal (0.74 nmol/l), corticosterone was undetectable (<0.5 nmol/l) and aldosterone was decreased (0.12 nmol/l nv: 0.8-1.2 nmol/l). At this time point, ACTH was <4 pg/ml, renin 1.6 mIU/l, LH 0.7 mIU/l and FSH 24.5 mIU/ml. This case demonstrated that isolated ACTH deficiency should be considered as a potential differential diagnosis in complete adrenal steroid insufficiency in newborns. Our data suggest that ACTH is not only necessary for cortisol biosynthesis but also for sufficient mineralocorticoid and androgen production by the adrenals in neonates. Presentation: 6/3/2024