CBS can be classified into responsive to pyridoxine (approximately 50% of cases), caused by milder mutations affecting cofactor binding or folding, often associated with milder phenotypes and later onset and responding to high-dose pyridoxine (100–500 mg/day), and pyridoxine-unresponsive CBS deficiency caused by severe enzyme defects, requiring dietary methionine restriction. Here, CBS is linked to homocystinuria.