An inactive cytochrome P450 CYP2D6 allele containing a deletion and a base substitution

Area of Science:

• Pharmacogenomics
• Molecular biology
• Enzyme kinetics

Background:

• Cytochrome P450 CYP2D6 is a key drug-metabolizing enzyme with significant genetic variability.
• Approximately 5%-10% of Caucasians are poor metabolizers due to CYP2D6 deficiency.
• Existing knowledge identifies most mutations causing CYP2D6 deficiency, but some phenotype-genotype discrepancies remain unexplained.

Purpose of the Study:

• To investigate the genetic basis of anomalous phenotype-genotype relationships in CYP2D6.
• To identify novel mutations in CYP2D6 responsible for poor metabolizer phenotypes despite heterozygous genotypes for common alleles.

Main Methods:

• Sequencing of all nine exons and intron-exon boundaries of the CYP2D6 gene.
• Phenotypic assessment of drug metabolism.
• Genotyping for common CYP2D6 mutant alleles.
• Analysis of allele frequency in a White American population.

Main Results:

• A single base-pair deletion (T1795) in exon 3, leading to premature termination and a truncated protein.
• A base substitution (G2064A) in exon 4, resulting in a G212E amino acid substitution.
• The newly identified CYP2D6 allele had a frequency of 0.01 in 50 White Americans.
• These mutations explain some previously observed anomalous genotype/phenotype relationships for CYP2D6.

Conclusions:

• Discovery of novel CYP2D6 mutations contributing to poor metabolizer phenotypes.
• These findings improve the understanding of CYP2D6 genetic variability and its clinical implications.
• The identified mutations provide a genetic explanation for certain unexplained CYP2D6 poor metabolizer cases.