Timely Diagnosis of Cobalamin C Disease via Rapid Genome Sequencing in a Neonate With Severe Prenatally Detected Biventricular Dysfunction

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Abstract
Cobalamin C (Cbl‐C) disease, the most common inborn error of cobalamin metabolism caused by biallelic pathogenic MMACHC variants, leads to multisystem involvement from methylmalonic acid and homocysteine accumulation. When diagnosed early, it is treatable. Rapid genome sequencing (GS) is becoming increasingly accessible and enables timely diagnosis and prompt treatment. We report a neonate who had severely decreased prenatal and postnatal biventricular function requiring inotropic support. Given the critically ill condition and unclear etiology, rapid GS was obtained and revealed homozygous pathogenic MMACHC variants, confirming a diagnosis of Cbl‐C disease. This prompted the early initiation of treatment with high‐dose hydroxocobalamin, betaine, levocarnitine, and folic acid. His cardiac function gradually improved, and he was discharged at 28 days of life. Critical care providers should suspect treatable inherited metabolic disorders in patients with unexplained presentations and recognize rapid GS as a powerful tool for early identification and treatment in critically ill patients.

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