The NT5C3A gene at 7p14.3 codes the 336 amino acid chain that is processed to cytosolic 5'-nucleotidase 3A. Its various isoforms are expressed in different cell lines. Thus isoform 4 is only expressed in reticulocytes (although isoforms 1 and 3 are also expressed in reticulocytes]]). Isoform 2 which contains the first 50 coded amino acids is found bound to the endoplasmic reticulum and induced by interferon alpha. Variations if dysfunctional, are the cause of P5N deficiency (P5ND). This is an autosomal recessive haemolytic anaemia with marked basophilic stippling. It is similar to the anaemia of lead poisoning as lead inhibits this enzyme, amongst others.