Atypical presentation of infantile cystinosis mimicking Bartter syndrome with concurrent hyperlipidemia and oromotor dysfunction: a case report

Infants with nephropathic cystinosis can rarely present with paradoxical hypokalemic metabolic alkalosis mimicking Bartter syndrome, delaying diagnosis. Herein, we present the case of a 14-month-old girl born to consanguineous parents, who presented with severe failure to thrive, persistent vomiting, and gross motor delay. Initial evaluation revealed stage 2 acute kidney injury, hyperlipidemia, severe hypokalemia, and elevated renin and aldosterone levels. Although the biochemical profile initially suggested Bartter syndrome, persistent hypophosphatemia in combination with severe oromotor dysfunction prompted genetic testing, revealing a homozygous, likely pathogenic variant in exon 7 of CTNS, which encodes cystinosin (c.422C>T; p.Ser141Phe). Fluid, electrolyte, and nutritional rehabilitation successfully corrected volume depletion and electrolyte imbalance. However, an underlying proximal renal tubular defect was unmasked as the patient transitioned to metabolic acidosis. The transient alkalosis was driven by severe polyuria and volume contraction, which temporarily masked the expected proximal bicarbonate wasting. Both hyperlipidemia and metabolic alkalosis improved during follow-up. Cystinosis should be considered in the differential diagnosis of infants presenting with an unexplained Bartter-like phenotype to prevent critical delays in initiating lifesaving cysteamine therapy.