ADH5 and Fanconi anemia: This is provided by a two-tiered protection system that consists of the enzymes alcohol dehydrogenase 5 (ADH5) and aldehyde dehydrogenase 2 (ALDH2) that detoxify this aldehyde (Tier-1) (2, 3) and two DNA repair pathways: Fanconi anemia and transcriptional coupled nucleotide excision repair (Tier-2) that repair DNA damage caused by formaldehyde (4, 5).