The spectrum of clinical phenotypes that are caused by BCS1L gene variants ranges from severe growth restriction, aminoaciduria, cholestasis, iron overload, lactic acidosis and early death syndrome (growth restriction, aminoaciduria, cholestasis, iron overload, lactic acidosis and early death) to multisystemic CIII deficiency, which is characterized by encephalopathy of variable severity, proximal tubulopathy and liver failure and mild Björnstad syndrome with sensorineural hearing loss and a brittle hair condition known as pili torti. The gene discussed is BCS1L; the disease is Björnstad syndrome.