ADH5 and Down syndrome: Moreover, ADH5 and Cocayne syndrome B (CSB, a member of the transcription-coupled nucleotide excision repair = TC-NER) provide Tier-1 and Tier-2 protection, respectively, against DPCs and ICLs caused by endogenous formaldehyde in the brain and kidney cells [8, 51, 53, 54] whereas ADH5 and FA protect the liver, kidney and hematopoietic cells [2].