The Impact of CYP2D6 and CYP2C19 Polymorphisms on Suicidal Behavior and Substance Abuse Disorder Among Patients With Schizophrenia: A Retrospective Study

CYP2D6 ultra-rapid metabolizer phenotype not associated with attempted suicide in a large sample of psychiatric inpatients

AIM

Suicide accounts for over 800,000 deaths per year worldwide and is the tenth-leading cause of mortality in USA. Several studies have investigated cytochrome P450 CYP2D6 ultra-rapid metabolizer (UM) phenotype in relation to suicidality, with mixed results. This study tested the hypothesis of increased suicide risk among CYP2D6 UMs.

PATIENTS & METHODS

Among the 4264 state psychiatric hospital inpatients included, 2435 (57%) reported a prior suicide attempt.

RESULTS

No association between UM status and attempted suicide was observed in bivariate (odds ratio: 0.87; 95% CI: 0.53-1.25), multivariate (adjusted odds ratio: 0.89; 95% CI: 0.55-1.46), or risk-stratified analyses.

CONCLUSION

These results contrast with prior reports of increased suicidality among CYP2D6 UMs and highlight the pressing need to identify reliable screening methods to better address this persistent public health problem.

Pharmacogenetics of drug oxidation via cytochrome P450 (CYP) in the populations of Denmark, Faroe Islands and Greenland

Denmark, the Faroe Islands and Greenland are three population-wise small countries on the northern part of the Northern Hemisphere, and studies carried out here on the genetic control over drug metabolism via cytochrome P450 have led to several important discoveries. Thus, CYP2D6 catalyzes the 2-hydroxylation, and CYP2C19 in part catalyzes the N-demethylation of imipramine. The phenomenon of phenocopy with regard to CYP2D6 was first described when Danish patients changed phenotype from extensive to poor metabolizers during treatment with quinidine. It was a Danish extensive metabolizer patient that became a poor metabolizer during paroxetine treatment, and this was due to the potent inhibition of CYP2D6 by paroxetine, which is also is metabolized by this enzyme. Fluoxetine and norfluoxetine are also potent inhibitors of CYP2D6, and fluvoxamine is a potent inhibitor of both CYP1A2 and CYP2C19. The bioactivation of proguanil to cycloguanil is impaired in CYP2C19 poor metabolizers. The O-demethylation of codeine and tramadol to their respective my-opioid active metabolites, morphine and (+)-O-desmethyltramadol was markedly impaired in CYP2D6 poor metabolizers compared to extensive metabolizers, and this impairs the hypoalgesic effect of the two drugs in the poor metabolizers. The frequency of CYP2D6 poor metabolizers is 2%-3% in Greenlanders and nearly 15% in the Faroese population. The frequency of CYP2C19 poor metabolizers in East Greenlanders is approximately 10%. A study in Danish mono and dizygotic twins showed that the non-polymorphic 3-N-demethylation of caffeine catalyzed by CYP1A2 is subject to approximately 70% genetic control.

A combined high CYP2D6-CYP2C19 metabolic capacity is associated with the severity of suicide attempt as measured by objective circumstances

This study examined, for the first time, whether a high CYP2D6-CYP2C19 metabolic capacity combination increases the likelihood of suicidal intent severity in a large study cohort. Survivors of a suicide attempt (n=587; 86.8% women) were genotyped for CYP2C19 (*2, *17) and CYP2D6 (*3, *4, *4xN, *5, *6, *10, wtxN) genetic variation and evaluated with the Beck Suicide Intent Scale (SIS). Patients with a high CYP2D6-CYP2C19 metabolic capacity showed an increased risk for a severe suicide attempt (P<0.01) as measured by the SIS-objective circumstance subscale (odds ratio (OR)=1.37; 95% confidence interval (CI)=1.05-1.78; P=0.02) after adjusting for confounders (gender, age, level of studies, marital status, mental disorders, tobacco use, family history of suicide, personal history of attempts and violence of the attempt). Importantly, the risk was greater in those without a family history of suicide (OR=1.82; CI=1.19-2.77; P=0.002). Further research is warranted to evaluate whether the observed relationship is mediated by the role of CYP2D6 and CYP2C19 involvement in the endogenous physiology or drug metabolism or both.

Detection and characterization of the CYP2D6*9x2 gene duplication in two Spanish populations: resolution of AmpliChip CYP450 test no-calls

BACKGROUND

CYP2D6 is a major drug-metabolizing enzyme. Polymorphic variation includes copy number variants such as gene deletions, duplications and multiplications of functional and nonfunctional gene units. In this article we describe the first systematic characterization of a CYP2D6*9x2 gene duplication. CYP2D6*9 is an allelic variant conferring reduced enzymatic activity. This novel gene duplication was discovered in two unrelated Spanish psychiatric patients. Both subjects were initially tested with the AmpliChip CYP450 test, which indicated the presence of a duplication and the CYP2D6*9 allele, but did not make a genotype call. The goal of the study was to resolve this issue by characterizing the CYP2D6 gene locus in these patients.

MATERIALS & METHODS

Both individuals and one offspring were regenotyped using our own CYP2D6 genotyping strategy employing long-range PCR and TaqMan-based SNP detection. In addition, gene resequencing and genotyping of duplication-specific long-range PCR products and quantitative gene copy number analysis was applied.

RESULTS

The duplication was mapped to the CYP2D6*9 allele and copy number analysis determined a CYP2D6*9x2 gene duplication in all three individuals. Because CYP2D6*9x2 is not recognized by the AmpliChip CYP450 test, this structural arrangement was responsible for the 'no call' on the AmpliChip CYP450 test report.

CONCLUSION

The full characterization of this allele will aid in the interpretation of AmpliChip CYP450 test results for clinical and research applications. Original submitted 8 June 2011; Revision submitted 18 July 2011.

Pharmacogenetics and forensic toxicology

Large inter-individual variability in drug response and toxicity, as well as in drug concentrations after application of the same dosage, can be of genetic, physiological, pathophysiological, or environmental origin. Absorption, distribution and metabolism of a drug and interactions with its target often are determined by genetic differences. Pharmacokinetic and pharmacodynamic variations can appear at the level of drug metabolizing enzymes (e.g., the cytochrome P450 system), drug transporters, drug targets or other biomarker genes. Pharmacogenetics or toxicogenetics can therefore be relevant in forensic toxicology. This review presents relevant aspects together with some examples from daily routines.