Asymptomatic Maternal Combined Homocystinuria and Methylmalonic Aciduria (cblC) Detected through Low Carnitine Levels on Newborn Screening

A symptom-free woman gave birth to a girl with a low carnitine level on newborn screening. The baby was unaffected, but the mother had biochemical abnormalities and mutations characteristic of the cblC defect of vitamin B12 metabolism (late-onset form). This patient with cblC was detected through her infant's newborn screening.