Renal Tubular Acidosis With High Anion Gap: A Report of Two Cases

We report two children, one aged three years and six months and another five years and seven months, who presented with growth failure and progressive skeletal deformities.On examination, they had short stature, frontal bossing, rachitic rosary, Harrison sulcus, pectus carinatum, widened wrists, and genu valgum, suggestive of rickets.The X-rays of the wrist joints showed typical features like metaphyseal cupping, fraying, splaying and widening of the growth plate.Further investigations revealed metabolic acidosis with a high anion gap and urine pH >5.5.There was hypokalemia, hypercalciuria, and phosphaturia in both patients, and one of the patients also had nephrocalcinosis, suggestive of distal renal tubular acidosis.The delta gap ratios in the two children were 0.8 and 0.57, respectively, suggestive of mixed high-and normalanion-gap metabolic acidosis.The presence of high-anion-gap metabolic acidosis led to further investigations.The urinary organic acid profiling revealed elevated 2-deoxytetronic acid, phenylacetic acid, thioglycolic acid, palmitic acid, and malonic acid, suggestive of an additional organic acid metabolic disturbance.So, the final diagnosis of distal renal tubular acidosis with an additional organic acid metabolic disturbance was made and managed with alkali (sodium bicarbonate), potassium supplementation for correction of hypokalemia, levocarnitine, biotin, and vitamin B12 as metabolic supportive therapy.On subsequent follow-up at six months, there was clinical improvement, normalization of blood pH, and anion gap.These cases highlight the importance of evaluation for an additional organic acid metabolic disturbance in patients with renal tubular acidosis and high anion gap.