Multiple Carboxylase Deficiency in an Infant Presenting With Severe Metabolic Acidosis and Sepsis-Like Features: A Case Report and Literature Review.

Multiple carboxylase deficiency (MCD) is a rare, treatable inborn error of biotin metabolism that may present in children in the first year of life with life-threatening metabolic crises. We report a 4-month-old child presenting with persistent seizures, eczematous rash near the orifices, unjustified loss of hair with baldness, and severe metabolic acidosis, initially mimicking septicemia. Urine organic acid investigation showed elevated levels of 3-hydroxyisovaleric acid, 3-methylcrotonylglycine, 3-hydroxypropionic acid, methylcitrate, and lactate that lead towards MCD. This diagnosis remains unconfirmed, as confirmatory testing (serum biotinidase activity and genetic analysis) was not available at our center. Early initiation of biotin (10 mg/day) led to rapid clinical and biochemical recovery. This particular case depicts the importance of biotin-responsive metabolic disorders in the first year of a child presenting with the classic triad of seizures, dermatitis, and alopecia with metabolic acidosis. Early recognition and prompt initiation of biotin therapy can result in rapid clinical recovery. Timely diagnosis is crucial to prevent avoidable morbidity and long-term neurological sequelae. This case highlights the importance of considering MCD in children. In the first year of life, unexplained metabolic acidosis as timely treatment can be lifesaving.