Fig. 1. (  A ) Detection of the μ-opioid receptor gene  OPRM1:c.118A>G single-nucleotide polymorphism (SNP) in two subjects by restriction-length polymorphism analysis. After amplification of part of  OPRM1 exon 1 using modified primer Oprm1F, the polymerase chain reaction products were digested with the restriction enzyme  Bst UI to detect the  OPRM1:c.118A>G SNP. The OPRM1:c.115G>C substitution generated by primer Oprm1F in combination with the  OPRM1:c.118A>G SNP creates an extra  Bst UI site within the 193-base pair (bp) polymerase chain reaction product, resulting in fragments of 24 and 169 bp after restriction digestion (  left ). (  B ) The 193-bp polymerase chain reaction product containing  OPRM1:c.118A is not cut. Subject 2 is an  OPRM1:c.118GA heterozygote as indicated by the presence of 193-bp and 169-bp bands. Subject 3 is an  OPRM1:c.118AA homozygote (193-bp band only, right). M = marker. (  C ) Confirmation of the presence of the  OPRM1:c.118A>G SNP by direct sequence analysis. Subject 2 is an  OPRM1:c.118GA heterozygote, whereas subject 3 is an  OPRM1:c.118AA homozygote. The position of the G116C substitution generated by primer Oprm1F to create the  Bst UI restriction site on the  OPRM1:c.118G allele is indicated by an  asterisk .