Aldehyde dehydrogenase 1A1 (ALDH1A1) is a member of the ALDH gene superfamily. Aldehyde dehydrogenases (ALDHs) are responsible for the metabolism of aldehydes (exogenous and endogenous) through NAD(P) + -dependent oxidation to their corresponding carboxylic acids or CoA esters. Different biological functions have been attributed to the different ALDH family members. The cytosolic enzyme ALDH1A1 is involved in the catalysis of retinol (vitamin A) metabolite retinaldehyde to retinoic acid (RA). RA acts as a ligand for the nuclear receptors retinoic receptor (RAR) and the retinoid X receptor (RXR) and therefore regulates the transcriptional activity of genes involved in multiple important processes including proliferation, differentiation, and apoptosis.

The purine nucleoside phosphorylase gene (PNP) encodes an enzyme which reversibly catalyzes the phosphorolysis of purine nucleosides. PNP is ubiquitously expressed in mammalian cells and tissues. PNP mutations cause nucleoside phosphorylase deficiency which result in defective T cell mediated immunity but can also affect B cell immunity and antibody responses.