Identification and characterization of CYP2D6*56B, an allele associated with the poor metabolizer phenotype.

A 5-year-old African-American girl presented with a CYP2D6*4xN/*10 genotype that was discordant with her poor metabolizer phenotype determined with the probe drug dextromethorphan. Both phenotype and genotype were confirmed in repeat assessments, suggesting that the CYP2D6*10 allele carried a novel debilitating sequence variation(s). The rationale for this study was to resolve the discordance and to describe the novel non-functional allelic variant of CYP2D6 and its frequency in populations of different ethnic backgrounds.

Cytochrome P4502D6 (CYP2D6) gene locus heterogeneity: characterization of gene duplication events.

Duplications and multiplications of active CYP2D6 genes can cause ultrarapid drug metabolism and lead to therapeutic failure. Multiple functional and non-functional duplication alleles have been further characterized. Duplications were detected by long-range polymerase chain reaction (PCR), PCR-restriction fragment length polymorphism, and sequence analysis. A PCR fragment encompassing the entire duplicated gene was utilized for detailed characterization. Duplications occurred at 1.3, 5.75, and 2.0% in Caucasian, African American, and racially mixed populations, respectively (n=887 total). Of those 28, 47, and 17% were non-functional CYP2D6*4 x N. Twelve unique duplication alleles were detected: *1 x N, *2 x N, *4 x N, *6 x N, *10 x N, *17 x N, *17 x N[spacer], *29 x N, *35 x N, *43 x N, *45 x N, and a novel non-functional tandem arrangement of a chimeric 2D7/2D6 and *1 gene. All novel duplications except *35 x N were found in African Americans. Accurate identification of gene duplication events is essential to avoid false-positive ultrarapid metabolism assignments and thus, overestimation of predicted activity and increased risk for unwanted adverse events.

Pediatric acetaminophen overdose: risk factors associated with hepatocellular injury.

OBJECTIVES: To characterize demographic and clinical factors associated with pediatric acetaminophen overdose and identify risk factors for hepatocellular injury. DESIGN: Retrospective 10-year chart review. SETTING: Two regional children's hospitals. MATERIALS AND METHODS: Records of patients examined because of acetaminophen ingestion from January 1, 1988, through December 31, 1997, were reviewed. Hepatocellular injury was defined as elevation of serum aminotransferase levels greater than 2 times the reference values. Severe hepatotoxic effect was defined as hepatotoxic effect with evidence of encephalopathy and/or coagulopathy. RESULTS: Data from 322 patients (208 girls and 114 boys, aged 1-17 years) were obtained. Ingestions were intentional in 140 patients (median age, 14 years) and unintentional in 172 (median age, 2 years). Another 10 cases represented dosing errors with therapeutic intent (median age, 3.5 years). Twenty-seven patients had hepatocellular injury; of these, 4 had severe hepatotoxic effects and 1 died. Hepatocellular injury occurred in 10.0% of the dosing error group, 17.9% of the intentional group, and 0.6% of the unintentional group. No patients underwent liver transplantation. Hepatocellular injury was associated with presentation longer than 24 hours after ingestion (odds ratio [OR], 335.0; 95% confidence interval [CI], 40.8-275.0), age 10 to 17 years (OR, 36.9; 95% CI, 4.9-275.4), intentional overdose (OR, 37.2; 95% CI, 5.0-278.2), dose greater than 150 mg/kg (OR, 17.9; 95% CI, 2.3-139.2), and white race (OR, 2.8; 95% CI, 1.1-7.2). CONCLUSIONS: Intentional and unintentional acetaminophen overdoses occurred with similar frequency. Therapeutic misadventure was relatively uncommon, as was hepatocellular injury. Practitioners should have greater suspicion of acetaminophen-associated hepatocellular injury in patients who present more than 24 hours after ingestion, older children, and those who have intentional ingestion.

Identification and characterization of novel sequence variations in the cytochrome P4502D6 (CYP2D6) gene in African Americans.

Cytochrome P4502D6 (CYP2D6) genotyping reliably predicts poor metabolizer phenotype in Caucasians, but is less accurate in African Americans. To evaluate discordance we have observed in phenotype to genotype correlation studies, select African American subjects were chosen for complete resequencing of the CYP2D6 gene including 4.2 kb of the CYP2D7-2D6 intergenic region. Comparisons were made to a CYP2D6(*)1 reference sequence revealing novel SNPs in the upstream, coding and intervening sequences. These sequence variations, defining four functional alleles (CYP2D6(*)41B, (*)45A and B and (*)46), were characterized for their ability to influence splice site strength, transcription level or catalytic protein activity. Furthermore, their frequency was determined in a population of 251 African Americans. A -692(TGTG) deletion (CYP2D6(*)45B) did not significantly decrease gene expression, nor could any other upstream SNP explain a genotype-discordant case. CYP2D6(*)45 and (*)46 have a combined frequency of 4% and can be identified by a common SNP. Carriers are predicted to exhibit an extensive or intermediate CYP2D6 phenotype.