Virtual twins for model-informed precision dosing of clozapine in patients with treatment-resistant schizophrenia.

Model-informed precision dosing using virtual twins (MIPD-VTs) is an emerging strategy to predict target drug concentrations in clinical practice. Using a high virtualization MIPD-VT approach (Simcyp version 21), we predicted the steady-state clozapine concentration and clozapine dosage range to achieve a target concentration of 350 to 600 ng/mL in hospitalized patients with treatment-resistant schizophrenia (N = 11). We confirmed that high virtualization MIPD-VT can reasonably predict clozapine concentrations in individual patients with a coefficient of determination (R2 ) ranging between 0.29 and 0.60. Importantly, our approach predicted the final dosage range to achieve the desired target clozapine concentrations in 73% of patients. In two thirds of patients treated with fluvoxamine augmentation, steady-state clozapine concentrations were overpredicted two to four-fold. This work supports the application of a high virtualization MIPD-VT approach to inform the titration of clozapine doses in clinical practice. However, refinement is required to improve the prediction of pharmacokinetic drug-drug interactions, particularly with fluvoxamine augmentation.

Delineating gene-environment effects using virtual twins of patients treated with clozapine.

Studies that focus on individual covariates, while ignoring their interactions, may not be adequate for model-informed precision dosing (MIPD) in any given patient. Genetic variations that influence protein synthesis should be studied in conjunction with environmental covariates, such as cigarette smoking. The aim of this study was to build virtual twins (VTs) of real patients receiving clozapine with interacting covariates related to genetics and environment and to delineate the impact of interacting covariates on predicted clozapine plasma concentrations. Clozapine-treated patients with schizophrenia (N = 42) with observed clozapine plasma concentrations, demographic, environmental, and genotype data were used to construct VTs in Simcyp. The effect of increased covariate virtualization was assessed by performing simulations under three conditions: "low" (demographic), "medium" (demographic and environmental interaction), and "high" (demographic and environmental/genotype interaction) covariate virtualization. Increasing covariate virtualization with interaction improved the coefficient of variation (R2 ) from 0.07 in the low model to 0.391 and 0.368 in the medium and high models, respectively. Whereas R2 was similar between the medium and high models, the high covariate virtualization model had improved accuracy, with systematic bias of predicted clozapine plasma concentration improving from -138.48 ng/ml to -74.65 ng/ml. A high level of covariate virtualization (demographic, environmental, and genotype) may be required for MIPD using VTs.

Pharmacogenomics in psychiatry - the challenge of cytochrome P450 enzyme phenoconversion and solutions to assist precision dosing.

Pharmacogenomic (PGx) testing of cytochrome P450 (CYP) enzymes may improve the efficacy and/or safety of some medications. This is facilitated by increased availability and affordability of genotyping, the development of clinical practice PGx guidelines and regulatory support. However, the common occurrence of CYP phenoconversion, a mismatch between genotype-predicted CYP phenotype and the actual CYP phenotype, currently limits the application of PGx testing for precision dosing in psychiatry. This review proposes a stepwise approach to assist precision dosing in psychiatry via the introduction of PGx stewardship programs and innovative PGx education strategies. A future perspective on delivering precision dosing for psychiatrists is discussed that involves innovative clinical decision support systems powered by model-informed precision dosing.

Quantifying the Impact of Phenoconversion on Medications With Actionable Pharmacogenomic Guideline Recommendations in an Acute Aged Persons Mental Health Setting.

Introduction: Polypharmacy and genetic variants that strongly influence medication response (pharmacogenomics, PGx) are two well-described risk factors for adverse drug reactions. Complexities arise in interpreting PGx results in the presence of co-administered medications that can cause cytochrome P450 enzyme phenoconversion. Aim: To quantify phenoconversion in a cohort of acute aged persons mental health patients and evaluate its impact on the reporting of medications with actionable PGx guideline recommendations (APRs). Methods: Acute aged persons mental health patients (N = 137) with PGx and medication data at admission and discharge were selected to describe phenoconversion frequencies for CYP2D6, CYP2C19 and CYP2C9 enzymes. The expected impact of phenoconversion was then assessed on the reporting of medications with APRs. Results: Post-phenoconversion, the predicted frequency at admission and discharge increased for CYP2D6 intermediate metabolisers (IMs) by 11.7 and 16.1%, respectively. Similarly, for CYP2C19 IMs, the predicted frequency at admission and discharge increased by 13.1 and 11.7%, respectively. Nineteen medications with APRs were prescribed 120 times at admission, of which 50 (42%) had APRs pre-phenoconversion, increasing to 60 prescriptions (50%) post-phenoconversion. At discharge, 18 medications with APRs were prescribed 122 times, of which 48 (39%) had APRs pre-phenoconversion, increasing to 57 prescriptions (47%) post-phenoconversion. Discussion: Aged persons mental health patients are commonly prescribed medications with APRs, but interpretation of these recommendations must consider the effects of phenoconversion. Adopting a collaborative care model between prescribers and clinical pharmacists should be considered to address phenoconversion and ensure the potential benefits of PGx are maximised.

Uptake of prenatal diagnostic testing and the effectiveness of prenatal screening for Down syndrome.

OBJECTIVES: To map prenatal screening and diagnostic testing pathways in Victorian pregnant women during 2003 to 2004; measure the impact of prenatal diagnostic testing uptake on the effectiveness of prenatal screening for Down syndrome; and assess factors influencing uptake of diagnostic testing following screening. METHODS: State-wide data collections of prenatal screening and diagnostic tests were linked to all Victorian births and pregnancy terminations for birth defects. RESULTS: Overall, 52% of women had a prenatal test (65 692/126 305); screening (44.9%), diagnostic testing (3.9%), or both (3.2%). Uptake of diagnostic testing was 71.4% (2390/3349) after an increased risk screen result, and 2.5% (1381/54 286) after a low risk result. Variation in uptake of diagnostic testing reduced the effectiveness of the screening program by 11.2%: from 87.4% (sensitivity - 125/143) to 76.2% (prenatal diagnoses of Down syndrome - 109/143). In both the increased and low risk groups, uptake was influenced by absolute numerical risk, as well as by the change in numerical risk from a priori risk. CONCLUSIONS: This comprehensive follow-up demonstrates clearly that numerical risk is being used to aid in decision making about confirmatory diagnostic testing. Collectively, these fundamental individual decisions will impact on the overall effectiveness of screening programmes for Down syndrome.

Multidrug-resistant genotype (ABCB1) and seizure recurrence in newly treated epilepsy: data from international pharmacogenetic cohorts.

PURPOSE: The association between a specific polymorphism (3435C>T) in the ABCB1 gene, coding for the membrane drug transporter P-glycoprotein (PgP), and pharmacoresistance to seizure control is controversial. Studies have been limited by multiple drug use, chronic cohorts with varying definitions, and retrospective clinical data. Herein we examine the relationship of this polymorphism with seizure recurrence in three independent international cohorts of patients newly treated for epilepsy. METHODS: Data were collected on demographics, medication details, and seizure control after 12 months of treatment. The distribution of ABCB1 3435C>T genotypes was compared between patients with and without recurrent unprovoked seizures. RESULTS: Five hundred forty-two newly treated patients were enrolled (212 from Australia, 285 from Scotland, and 45 from Hong Kong). A total of 38.4% had recurrent unprovoked seizures after starting antiepileptic drug (AED) treatment. Genotype frequencies and ethnicity did not differ between the Scottish and Australian cohorts, but both were significantly different in the Hong Kong cohort. There was no significant relationship between the ABCB1 3435C>T genotype and the rate of recurrence of unprovoked seizures in the three cohorts individually or combined; however the epilepsy syndrome and a greater number of seizures pretreatment was associated with an increased risk of seizure recurrence. CONCLUSIONS: The ABCB1 3435C>T genotype does not have a major role in determining the efficacy of seizure control with initial AED therapy. The study highlights issues that arise in combining pharmacogenetic datasets from different ethnic regions and health systems, an approach that is essential to advance this field.

Multicentre search for genetic susceptibility loci in sporadic epilepsy syndrome and seizure types: a case-control study.

BACKGROUND: The Epilepsy Genetics (EPIGEN) Consortium was established to undertake genetic mapping analyses with augmented statistical power to detect variants that influence the development and treatment of common forms of epilepsy. METHODS: We examined common variations across 279 prime candidate genes in 2717 case and 1118 control samples collected at four independent research centres (in the UK, Ireland, Finland, and Australia). Single nucleotide polymorphism (SNP) and combined set-association analyses were used to examine the contribution of genetic variation in the candidate genes to various forms of epilepsy. FINDINGS: We did not identify clear, indisputable common genetic risk factors that contribute to selected epilepsy subphenotypes across multiple populations. Nor did we identify risk factors for the general all-epilepsy phenotype. However, set-association analysis on the most significant p values, assessed under permutation, suggested the contribution of numerous SNPs to disease predisposition in an apparent population-specific manner. Variations in the genes KCNAB1, GABRR2, KCNMB4, SYN2, and ALDH5A1 were most notable. INTERPRETATION: The underlying genetic component to sporadic epilepsy is clearly complex. Results suggest that many SNPs contribute to disease predisposition in an apparently population-specific manner. However, subtle differences in phenotyping across cohorts, combined with a poor understanding of how the underlying genetic component to epilepsy aligns with current phenotypic classifications, might also account for apparent population-specific genetic risk factors. Variations across five genes warrant further study in independent cohorts to clarify the tentative association.

Using record linkage and manual follow-up to evaluate the Victorian maternal serum screening quadruple test for Down's syndrome, trisomy 18 and neural tube defects.

OBJECTIVES: The Genetic Health Services Victoria maternal serum screening (MSS) quadruple test has been available to pregnant women in Victoria since 1996. The objectives of this study were to follow up the pregnancies screened by MSS between July 1998 and June 2000 and to determine the performance characteristics of the test for Down's syndrome, trisomy 18 and neural tube defects (NTDs). METHODS: MSS results were matched to pregnancy outcome information from the Perinatal Data Collection Unit and Birth Defects Register, using automated probabilistic record linkage. For unmatched pregnancies, manual follow-up was carried out by contacting referring doctors and hospitals, resulting in a very high follow-up rate of 99.2% (18,989/19,143). RESULTS: The sensitivity of MSS for Down's syndrome was 85% (23/27-95%CI 72-99%) with a falsepositive rate (FPR) of 6.8% (risk threshold >or= 1 in 250). While using a fixed 5% FPR, the sensitivity for Down's syndrome was slightly lower (78%). The sensitivity for trisomy 18 was 44% (4/9 - 95% CI 12-77%) with a FPR of 0.5% (risk threshold of >or= 1 in 200). 11 of the 15 (73 - 95%CI 51-97%) cases of open NTDs were detected from screening, with a 1% FPR (risk threshold alpha-fetoprotein [AFP] >or=2.5 MoM). All cases of anencephaly had increased AFP levels. CONCLUSION: Probabilistic record linkage and manual follow-up is an efficient method for ascertainment of pregnancy outcomes, with a higher follow-up rate than that reported in similar studies. MSS should remain an available option for all pregnant women in Victoria, with test characteristics comparable with other recent reports of the quadruple test.

Construction of a natural panel of 11p11.2 deletions and further delineation of the critical region involved in Potocki-Shaffer syndrome.

Potocki-Shaffer syndrome (PSS) is a contiguous gene deletion syndrome that results from haploinsufficiency of at least two genes within the short arm of chromosome 11[del(11)(p11.2p12)]. The clinical features of PSS can include developmental delay, mental retardation, multiple exostoses, parietal foramina, enlarged anterior fontanel, minor craniofacial anomalies, ophthalmologic anomalies, and genital abnormalities in males. We constructed a natural panel of 11p11.2-p13 deletions using cell lines from 10 affected individuals, fluorescence in situ hybridization (FISH), microsatellite analyses, and array-based comparative genomic hybridization (array CGH). We then compared the deletion sizes and clinical features between affected individuals. The full spectrum of PSS manifests when deletions are at least 2.1 Mb in size, spanning from D11S1393 to D11S1385/D11S1319 (44.6-46.7 Mb from the 11p terminus) and encompassing EXT2, responsible for multiple exostoses, and ALX4, causing parietal foramina. Yet one subject with parietal foramina whose deletion does not include ALX4 indicates that ALX4 in this subject may be rendered functionally haploinsufficient by a position effect. Based on comparative deletion mapping of eight individuals with the full PSS syndrome including mental retardation and two PSS families with no mental retardation, at least one gene related to mental retardation is likely located between D11S554 and D11S1385/D11S1319, 45.6-46.7 Mb from the 11p terminus.

The hunt for new genes and polymorphisms that can control the response to drugs.

There has been a great increase in the knowledge of understanding the genetic basis for individual variation in response to drugs. The study of variation in gene structure (polymorphism) can now predict the likely metabolic behavior in an individual for a number of drugs. This review documents the different strategies that can be used to find new genes and polymorphisms within these genes. Candidate genes can be used in case-control studies or studies where the parents of the person having an adverse effect from the drug are used as controls. New genes are being discovered in the drug development process and the technological development in molecular biology is expected to greatly enhance knowledge of the genes that regulate drug metabolism.

Bivariate variance-component analysis, with application to systolic blood pressure and total cholesterol levels in the Framingham Heart Study.

BACKGROUND: The correlations between systolic blood pressure (SBP) and total cholesterol levels (CHOL) might result from genetic or environmental factors that determine variation in the phenotypes and are shared by family members. Based on 330 nuclear families in the Framingham Heart Study, we used a multivariate normal model, implemented in the software FISHER, to estimate genetic and shared environmental components of variation and genetic and shared environmental correlation between the phenotypes. The natural logarithm of the phenotypes measured at the last visit in both Cohort 1 and 2 was used in the analyses. The antihypertensive treatment effect was corrected before adjustment of the systolic blood pressure for age, sex, and cohort. RESULTS: The univariate correlation coefficient was statistically significant for sibling pairs and parent-offspring pairs, but not significant for spouse pairs. In the bivariate analysis, the cross-trait correlation coefficients were not statistically significant for all relative pairs. The shared environmental correlation was statistically significant, but the genetic correlation was not significant. CONCLUSION: There is no significant evidence for a close genetic correlation between systolic blood pressure and total cholesterol levels. However, some shared environmental factors may determine the variation of both phenotypes.

Company Profile: GenesFX Health Pty Ltd.

GenesFX Health (Melbourne, Australia) is providing genetic testing with clinical interpretation to personalize how people take medications. The company's aim is to achieve the best health outcomes for patients by ensuring that the way they metabolize medications is included when doctors prescribe them medication. This would be achieved by introducing pharmacogenomics into medical practice to provide more informed prescribing, reduce side effects and create maximum efficacy of medications. Through the use of GenesFX Health innovative genetic test, DNAdose®, GenesFX Health is able to analyze the profile of a patient's genetic variation and maps this to the optimum drug and dosage for a specific treatment. The company's focus on the interpretation of genetic test results has led to the development of a Pharmacogenomic Database and Pharmacogenomic Interpretation System, which allows the team to communicate complex genetic test results in a meaningful way to doctors. There is a significant opportunity to expand GenesFX Health current model of delivering pharmacogenomic tests, by partnering with other laboratories around the world, making pharmacogenomics more accessible and clinically useful. Doctors using the service have welcomed the clinical guidance. Patients have felt relieved and empowered by understanding why they have adverse reactions to medications, and which medications and doses are most suited to them.

Clinical use of pharmacogenomic tests in 2009.

Pharmacogenomics is a new field where testing an individual can define either a risk status for an adverse event, or the rate of metabolism of a drug. This is achieved by the categorisation of the enzyme activity or documenting genetic polymorphisms of a metabolising enzyme. The best example of risk status assessment is the recent finding that HLA-B typing a person can predict whether they are at risk of a severe skin reaction from the drug abacavir. Those patients showing HLA-B*5701, who are being considered for abacavir therapy, can be prevented from developing potentially toxic epidermal necrosis (TEN) or Stevens-Johnson Syndrome by avoiding abacavir. The evidence for HLA-B typing for allopurinol and carbamazepine has also been described. Most other pharmacogenomic tests are of drug metabolising enzymes, which can either be assessed using "probe" drugs and measuring a ratio of parent drug to metabolite, or, by genetic testing for polymorphisms of the genes. In practice, testing is usually done by molecular testing, but this typically does not detect all polymorphisms. This article briefly reviews the evidence for the utilisation of pharmacogenomics for antidepressant drugs, tamoxifen, codeine, warfarin, azathioprine, clopidogrel, omeprazole, tacrolimus and irinotecan. There are few pharmacogenomics tests being carried out in practice, as there has not been a wide appreciation of their use, and only limited evidence exists for many individual drugs. It is expected that utilisation will increase as more evidence becomes available and there is a wider understanding of the existing evidence by the medical profession.

Multi-SNP pharmacogenomic classifier is superior to single-SNP models for predicting drug outcome in complex diseases.

OBJECTIVES: Most pharmacogenomic studies have attempted to identify single nucleotide polymorphism (SNP) markers that are predictive for treatment outcomes. It is, however, unlikely in complex diseases such as epilepsy, affecting heterogeneous populations, that a single SNP will adequately explain treatment outcomes. This study reports an approach to develop a multi-SNP model to classify treatment outcomes for such a disease and compares this with single-SNP models. METHODS: A prospectively collected dataset of outcomes in 115 patients newly treated for epilepsy, with genotyping for 4041 SNPs in 279 candidate genes, was used for the model development. A cross-validation-based methodology identified SNPs most influential in predicting seizure control after 1 year of drug treatment and then incorporated these into a multi-SNP classification model; using the k-Nearest Neighbour (kNN) supervised learning approach. The classifier was cross-validated to determine its effectiveness in predicting treatment outcome in the developmental cohort and then in two independent validation cohorts. In each, the classification by the multi-SNP model was compared with that of models using the individual SNPs alone. RESULTS: Five SNPs were selected for the multi-SNP model. Cross-validation showed that the multi-SNP model had a predictive accuracy of 83.5% in the developmental cohort and sensitivity and positive predictive values above 80% in both the independent validation cohorts. In all cases, the multi-SNP model classified the treatment outcomes better than those using any individual SNPs alone. CONCLUSION: The results show that a classifier using multiple SNPs can predict treatment outcome more reliably than single-SNP models. This multi-SNP classifier should be tested on data from newly diagnosed epilepsy populations to determine its broad clinical validity. Our method to developing a multi-SNP classifier could be applied to pharmacogenomic studies of other complex diseases.

Problems assessing uptake of Huntington disease predictive testing and a proposed solution.

The uptake of predictive testing for Huntington disease informs our understanding of decision making by those at risk and assists with planning for service provision. Uptake figures have been reported from several centers based on the total number of people who have undertaken predictive testing as a percentage of those estimated to be at 50% risk in the region. This method produced a figure of 35% from our own service, much higher than observation of the local pedigrees indicated, and higher than other published reports. We have identified some errors in the commonly used formula. The major errors are the use of the cumulative total of those who have had testing with a static denominator of those at 50% risk, and the failure to exclude from the at-risk group those who are too young and therefore ineligible to test.We report data from the Huntington Disease Register of Victoria and estimate the prevalence to be 8 per 100,000 in 1999. Additional data on individuals at risk were collated. We found that for every diagnosed person there were 4.2 individuals at 50% risk, a lower ratio than one to five hypothesized in the literature. We examined these ratios in the context of uptake.Significantly, we provide a solution to the calculation of uptake with a formula that factors in a dynamic denominator and corrects for the number of years testing has been offered. Using this formula, we calculated an uptake of 13.0-15.4% for the state of Victoria, Australia. This formula can be used to compare uptake across different centers.

Thiopurine methyltransferase and thiopurine metabolite testing in patients with inflammatory bowel disease who are taking thiopurine drugs.

Thiopurine methyltransferase genotyping and thiopurine metabolite testing has been established as an adjunct to monitoring patients taking thiopurine drugs. This special report describes the clinical implications for this type of testing for patients with inflammatory bowel disease who are taking thiopurine drugs. A total of 10% of patients were found to be intermediate metabolizers and the mean dosage (in mg/kg equivalent) was lower in intermediate metabolizers than extensive metabolizers. The metabolite levels did not correlate with scores measuring clinical severity but levels of 6-methylmercaptopurine were related to the dosage of the drugs. Despite considerable study of thiopurine methyltransferase testing in the literature, it is still not widely used in many geographical areas. This study adds to the evidence about using such testing as well as expanding the role of simultaneously measuring thiopurine metabolites. Further work is planned to evaluate the uptake when such testing becomes available locally as a clinical service.

Fifteen years of experience in predictive testing for Huntington disease at a single testing center in Victoria, Australia.

PURPOSE: This retrospective study describes 15 years of experience in predictive testing for Huntington disease at a single center in Victoria, Australia. METHOD: Data collected on 756 participants included age, gender, family history, prior risk and the age at which this risk became known, exposure to Huntington disease, number of children, and proximity to the testing center. RESULTS: Some 57.8% of participants were female, and 88.8% had a 50% risk of developing Huntington disease. The mean age at entry was 40.4 years and was gender-independent. Of all completed tests (n = 648), 37.5% gave high-risk results, and 3.2% were in the zone of reduced penetrance. The 14.3% who withdrew from testing tended to be younger and childless, lacked exposure to severe Huntington disease, and more often at 25% or less risk. Some 32.4% of candidates presented for testing within 1 year of becoming aware of their risk, and most of these individuals had little or no exposure to severe Huntington disease. Those whose exposure was considerable waited on average for more than 13 years. Among the most inexperienced candidates were a group of "adoptees" (raised away from their biological family). Maternal transmission was the source of risk for 19 of 20 adoptees. CONCLUSION: This study illustrates the significance of exposure to Huntington disease and its impact on the timing of testing.

Informed choice in women attending private clinics to undergo first-trimester screening for Down syndrome.

OBJECTIVES: Informed choice for prenatal screening has long been considered an essential aspect of service provision, and has been researched extensively in the second trimester. This study aims at examining whether women having first-trimester screening in a private clinic had made an informed choice. METHODS: A cross-sectional survey recruited women having first-trimester screening at specialist ultrasound practices. Two questionnaires containing a validated Multidimensional Measure of Informed Choice (MMIC) were self-administered pre- and post-screening. RESULTS: MMIC was completed by 81% (163/202) of women. Ninety-nine percent of women had a positive attitude towards screening, therefore informed choice was essentially measured on knowledge alone. Pre-screening, 68% made an informed choice, compared with 74% post-screening (chi2 = 1.6, p = 0.21 (McNemar)). Knowledge was associated with education level, information sources and perception of screening as routine or optional. CONCLUSIONS: The Australasian Guidelines on prenatal screening state that all women having testing should be provided with written information, and it should be ensured that they have appropriate understanding of the test(s). These guidelines are not being met, even in private clinical care. Health professionals should ensure that all women are provided with suitable information about prenatal screening that is tailored to their level of education and individual needs, and should emphasise that screening is optional.

Educating genetic counselors in Australia: developing an international perspective.

The demand for genetic counseling services is increasing worldwide. This paper highlights the Australian experience of genetic counselor education and the history of the profession. The relevance of local factors, including the health care system, the education system and the small population in the evolution of the 1-year training programs are considered as an alternative model for emerging programs. The development of the education and training processes compared to that of other countries namely the United States of America (USA), the United Kingdom (UK) and Canada is discussed. The importance of international collaborations between the programs, to facilitate academic discussion and possible curriculum innovations, and to maintain professional understanding between genetic counselors is emphasized. Core genetic counseling competencies have been published for the UK and USA and an Australian set is proposed. In conclusion future directions are considered, including international issues around genetic counseling certification, reciprocity, and the potential for an Australian role in training genetic counselors in South East Asia.

Longterm follow-up in chondrodysplasia punctata, tibia-metacarpal type, demonstrating natural history.

We report the longterm clinical and radiological progression in three unrelated patients with the tibia-metacarpal form of chondrodysplasia punctata (CDP-TM). The patients were followed for 37, 25, and 32 years, respectively. At follow-up intellectual function was normal, and physical function was well preserved. There was also marked resolution of several significant early radiographic features. The patients attained adult heights of 152, 138, and 148 cm. Two patients had chronic serous otitis media requiring tympanostomy tubes during childhood. One patient suffered persisting back pain related to spinal stenosis and required lumbar laminectomy at the age of 26 years. One patient had hip dysplasia requiring orthopedic surgical intervention. All patients had recurrent patella dislocation. Sterol and very long chain fatty acid profiles, FISH analysis for SHOX gene deletions, blood lymphocyte karyotype, and phytanic acid levels were normal in those tested, and no mutations in arylsulfatase D and E genes were detected. These data suggest that the longterm clinical and functional prognosis in this condition appears to be better than that expected based on initial clinical and radiological findings.