Global Adrenal Insufficiency in Two Independent Patients Carrying the Same Homozygous c.172A>G, p.(Thr58Ala) Mutation in the TBX19 Gene.

Introduction: TBX19 mutations cause isolated ACTH-deficiency. While this classically results in severe hypocortisolism, potential consequences for mineralocorticoid biosynthesis have not been described to date. Liquid chromatography mass spectrometry (LC-MS/MS) and gas chromatography mass spectrometry (GC-MS) allow novel insights into the steroid metabolism of pediatric endocrine diseases.

Case presentation: Patient 1 (female) presented right after birth with hypoglycemia and hyponatremia (minimum sodium 126 mmol/L). She recovered under therapy with hydrocortisone, fludrocortisone and initial NaCl. Patient 2 (male) presented after birth with prolonged cholestatic jaundice. Only at the age of 3.5 months, repeated episodes of hypoglycemia occurred. Both patients showed severely reduced ACTH. LC-MS/MS analyses on plasma samples demonstrated combined reduced glucocorticoid- and mineralocorticoid biosynthesis confirmed by GC-MS analyses on spot urine. In contrast to patient 1, patient 2 (currently 8 years old) never suffered from hyponatremia. Both patients carry the same homozygous c.172A>G, p.(Thr58Ala) mutation in the TBX19 gene proving isolated ACTH-deficiency.

Conclusion: Isolated ACTH-deficiency can be associated with reduced mineralocorticoids and hyponatremia. We hypothesize that sufficient pituitary ACTH secretion is an important predisposition for regular adrenal mineralocorticoid biosynthesis.