This case describes the diagnosis and management of an infant with clinically diagnosed aldosterone synthase deficiency (genetics pending). She is now being managed with medical therapy and is growing well.
A 5 month-old female infant was born at 40+4/40 weeks gestation to a 24yo primiparous woman, following an uneventful pregnancy. The infant’s birth weight was 3640g, length 51.0cm, head circumference of 34.5cm. She was formula-fed from birth with no issues initially over the first week or so of life. Subsequently she fed progressively more poorly tolerating only 30-40mL at a time and failed to gain weight and lost 4% of her birth weight.
Four days later she re-presented with no improvement in symptoms or weight gain and persistent marked hypotonia. Further investigations including MRI brain, serum ammonia, urine metabolic screen, and karyotype (46XX) were normal. Hyponatraemia was noted. Urine sodium excretion was inappropriately high (59 mmol/L). Cortisol (410 nmol/L, adult ref: 145-619), ACTH (1.6 pmol/L, ref: <20), and 17-hydroxyprogesterone (1.5 nmol/L, ref: 0.0-6.0) were all unremarkable. Aldosterone/renin showed renin above the upper detectable limit and aldosterone in the lower half of the adult reference range. The biochemical diagnosis of aldosterone synthase deficiency was made. Fludrocortisone 300microg PO daily and sodium chloride supplements 5mL PO TDS were commenced with good clinical effect and improvement in the plasma sodium and renin concentrations.
The likely aetiology of hyponatraemia differs with age at presentation ranging from excess total body water, most commonly due to the syndrome of inappropriate antidiuretic hormone secretion, in the first 5 days of life to low total body sodium of various aetiologies during the late newborn period from 6-28 days. A rare cause of infant hyponatraemia is congenital isolated hypoaldosteronism, an autosomal recessively inherited disorder of the CYP11B2 (aldosterone synthase) enzyme that catalyses the production of aldosterone from corticosterone.