Mutations due to single nucleotide polymorphism (SNP) of the gene encoding CYP 3A5 have been demonstrated to affect their expression. Among CYP3A5 alleles, CYP3A5*1 has been found to be the main allele associated with CYP 3A5 expression, whereas the mutant allele CYP3A5*3 prevents expression of the enzyme. Several studies have shown that this mutation affects the dosing of tacrolimus.