EMQN best practice guidelines for genetic testing in hereditary breast and ovarian cancer

Hereditary Breast and Ovarian Cancer (HBOC) is a genetic condition associated with increased risk of cancers. The past decade has brought about significant changes to hereditary breast and ovarian cancer (HBOC) diagnostic testing with new treatments, testing methods and strategies, and evolving information on genetic associations. These best practice guidelines have been produced to assist clinical laboratories in effectively addressing the complexities of HBOC testing, while taking into account advancements since the last guidelines were published in 2007. These guidelines summarise cancer risk data from recent studies for the most commonly tested high and moderate risk HBOC genes for laboratories to refer to as a guide. Furthermore, recommendations are provided for somatic and germline testing services with regards to clinical referral, laboratory analyses, variant interpretation, and reporting. The guidelines present recommendations where 'must' is assigned to advocate that the recommendation is essential; and 'should' is assigned to advocate that the recommendation is highly advised but may not be universally applicable. Recommendations are presented in the form of shaded italicised statements throughout the document, and in the form of a table in supplementary materials (Table S4). Finally, for the purposes of encouraging standardisation and aiding implementation of recommendations, example report wording covering the essential points to be included is provided for the most common HBOC referral and reporting scenarios. These guidelines are aimed primarily at genomic scientists working in diagnostic testing laboratories.

Alberta Spinal Muscular Atrophy Newborn Screening-Results from Year 1 Pilot Project

Spinal muscular atrophy (SMA) is a progressive neuromuscular disease caused by biallelic pathogenic/likely pathogenic variants of the survival motor neuron 1 (SMN1) gene. Early diagnosis via newborn screening (NBS) and pre-symptomatic treatment are essential to optimize health outcomes for affected individuals. We developed a multiplex quantitative polymerase chain reaction (qPCR) assay using dried blood spot (DBS) samples for the detection of homozygous absence of exon 7 of the SMN1 gene. Newborns who screened positive were seen urgently for clinical evaluation. Confirmatory testing by multiplex ligation-dependent probe amplification (MLPA) revealed SMN1 and SMN2 gene copy numbers. Six newborns had abnormal screen results among 47,005 newborns screened during the first year and five were subsequently confirmed to have SMA. Four of the infants received SMN1 gene replacement therapy under 30 days of age. One infant received an SMN2 splicing modulator due to high maternally transferred AAV9 neutralizing antibodies (NAb), followed by gene therapy at 3 months of age when the NAb returned negative in the infant. Early data show that all five infants made excellent developmental progress. Based on one year of data, the incidence of SMA in Alberta was estimated to be 1 per 9401 live births.

Methodology for clinical genotyping of CYP2D6 and CYP2C19

Many antidepressants, atomoxetine, and several antipsychotics are metabolized by the cytochrome P450 enzymes CYP2D6 and CYP2C19, and guidelines for prescribers based on genetic variants exist. Although some laboratories offer such testing, there is no consensus regarding validated methodology for clinical genotyping of CYP2D6 and CYP2C19. The aim of this paper was to cross-validate multiple technologies for genotyping CYP2D6 and CYP2C19 against each other, and to contribute to feasibility for clinical implementation by providing an enhanced range of assay options, customizable automated translation of data into haplotypes, and a workflow algorithm. AmpliChip CYP450 and some TaqMan single nucleotide variant (SNV) and copy number variant (CNV) data in the Genome-based therapeutic drugs for depression (GENDEP) study were used to select 95 samples (out of 853) to represent as broad a range of CYP2D6 and CYP2C19 genotypes as possible. These 95 included a larger range of CYP2D6 hybrid configurations than have previously been reported using inter-technology data. Genotyping techniques employed were: further TaqMan CNV and SNV assays, xTAGv3 Luminex CYP2D6 and CYP2C19, PharmacoScan, the Ion AmpliSeq Pharmacogenomics Panel, and, for samples with CYP2D6 hybrid configurations, long-range polymerase chain reactions (L-PCRs) with Sanger sequencing and Luminex. Agena MassARRAY was also used for CYP2C19. This study has led to the development of a broader range of TaqMan SNV assays, haplotype phasing methodology with TaqMan adaptable for other technologies, a multiplex genotyping method for efficient identification of some hybrid haplotypes, a customizable automated translation of SNV and CNV data into haplotypes, and a clinical workflow algorithm.

Data sharing to improve concordance in variant interpretation across laboratories: results from the Canadian Open Genetics Repository

BACKGROUND

This study aimed to identify and resolve discordant variant interpretations across clinical molecular genetic laboratories through the Canadian Open Genetics Repository (COGR), an online collaborative effort for variant sharing and interpretation.

METHODS

Laboratories uploaded variant data to the Franklin Genoox platform. Reports were issued to each laboratory, summarising variants where conflicting classifications with another laboratory were noted. Laboratories could then reassess variants to resolve discordances. Discordance was calculated using a five-tier model (pathogenic (P), likely pathogenic (LP), variant of uncertain significance (VUS), likely benign (LB), benign (B)), a three-tier model (LP/P are positive, VUS are inconclusive, LB/B are negative) and a two-tier model (LP/P are clinically actionable, VUS/LB/B are not). We compared the COGR classifications to automated classifications generated by Franklin.

RESULTS

Twelve laboratories submitted classifications for 44 510 unique variants. 2419 variants (5.4%) were classified by two or more laboratories. From baseline to after reassessment, the number of discordant variants decreased from 833 (34.4% of variants reported by two or more laboratories) to 723 (29.9%) based on the five-tier model, 403 (16.7%) to 279 (11.5%) based on the three-tier model and 77 (3.2%) to 37 (1.5%) based on the two-tier model. Compared with the COGR classification, the automated Franklin classifications had 94.5% sensitivity and 96.6% specificity for identifying actionable (P or LP) variants.

CONCLUSIONS

The COGR provides a standardised mechanism for laboratories to identify discordant variant interpretations and reduce discordance in genetic test result delivery. Such quality assurance programmes are important as genetic testing is implemented more widely in clinical care.

Retrospective testing of respiratory specimens for COVID-19 to assess for earlier SARS-CoV-2 infections in Alberta, Canada

Background: The first case of coronavirus disease 2019 (COVID-19) in Alberta, Canada, was confirmed on March 5, 2020. Because the virus testing criteria had changed significantly over this time period, we wanted to ascertain whether previous cases of COVID-19 had been missed in the province. Methods: Our aim was to retrospectively evaluate specimens submitted for respiratory virus testing from December 1, 2019, through March 7, 2020, for undetected severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections before the first confirmed case. Results: Testing of 23,517 samples (representing 23,394 patients) identified 1 patient positive for SARS-CoV-2. This specimen was collected on February 24, 2020, from a patient with symptoms consistent with COVID-19 who had recently returned from the western United States. Phylogenetic analysis confirmed this viral isolate belonged to lineage B.1. The epidemiology of this case is consistent with those of other early cases before sustained community transmission, which included a travel history outside of Canada. Conclusion: This exercise provides support that local public health pandemic planning was satisfactory and timely.

Identification of high-impact gene-drug pairs for pharmacogenetic testing in Alberta, Canada

OBJECTIVES

To facilitate decision-making and priority-setting related to Alberta's Pharmacogenomics (PGx) testing implementation strategy by identifying gene-drug pairs with the highest potential impact on prescribing practices in Alberta.

PATIENTS AND METHODS

Annual drug dispensing data for Alberta from 2012 to 2016 for 57 medications with PGx-based prescribing guidelines were obtained, along with population estimates and demographics (age and ethnicity). Frequencies of actionable PGx genotypes by ethnicity were obtained from the Pharmacogenomics Knowledgebase (PharmGKB). Annual dispensing activity for each of the 57 medications was calculated for the full population (all ages) and children/youth (0-19 years). Alberta ethnicity data were cross-referenced with genetic frequency data for each of the main ethnic groups from PharmGKB to estimate the proportion of individuals with actionable genotypes. Actionable genotype proportions and drug dispensing frequencies were collectively used to identify high impact gene-drug pairs.

RESULTS

We found (a) half of the drugs with PGx-based prescribing guidelines, namely, analgesics, proton pump inhibitors, psychotropics, and cardiovascular drugs, were dispensed at high frequencies (>1% of the entire population), (b) the dispensing rate for about one-third of these drugs increased over the 5-year study period, (c) between 1.1 and 45% of recipients of these drugs carried actionable genotypes, and (d) the gene-drug pairs with greatest impact in Alberta predominatly included CYP2C19 or CYP2D6.

CONCLUSIONS

We uncovered specific patterns in drug dispensing and identified important gene-drug pairs that will inform the planning and development of an evidenced-based PGx testing service in Alberta, Canada. Adaptation of our approach may facilitate the process of evidence-based PGx testing implementation in other jurisdictions.

MITO-FIND: A study in 390 patients to determine a diagnostic strategy for mitochondrial disease

Mitochondrial diseases, due to nuclear or mitochondrial genome mutations causing mitochondrial dysfunction, have a wide range of clinical features involving neurologic, muscular, cardiac, hepatic, visual, and auditory symptoms. Making a diagnosis of a mitochondrial disease is often challenging since there is no gold standard and traditional testing methods have required tissue biopsy which presents technical challenges and most patients prefer a non-invasive approach. Since a diagnosis invariably involves finding a disease-causing DNA variant, new approaches such as next generation sequencing (NGS) have the potential to make it easier to make a diagnosis. We evaluated the ability of our traditional diagnostic pathway (metabolite analysis, tissue neuropathology and respiratory chain enzyme activity) in 390 patients. The traditional diagnostic pathway provided a diagnosis of mitochondrial disease in 115 patients (29.50%). Analysis of mtDNA, tissue neuropathology, skin electron microscopy, respiratory chain enzyme analysis using inhibitor assays, blue native polyacrylamide gel electrophoresis were all statistically significant in distinguishing patients between a mitochondrial and non-mitochondrial diagnosis. From these 390 patients who underwent traditional analysis, we recruited 116 patients for the NGS part of the study (36 patients who had a mitochondrial diagnosis (MITO) and 80 patients who had no diagnosis (No-Dx)). In the group of 36 MITO patients, nuclear whole exome sequencing (nWES) provided a second diagnosis in 2 cases who already had a pathogenic variant in mtDNA, and a revised diagnosis (GLUL) in one case that had abnormal pathology but no pathogenic mtDNA variant. In the 80 NO-Dx patients, nWES found non-mitochondrial diagnosis in 26 patients and a mitochondrial diagnosis in 1 patient. A genetic diagnosis was obtained in 53/116 (45.70%) cases that were recruited for NGS, but not in 11/116 (9.48%) of cases with abnormal mitochondrial neuropathology. Our results show that a non-invasive, bigenomic sequencing (BGS) approach (using both a nWES and optimized mtDNA analysis to include large deletions) should be the first step in investigating for mitochondrial diseases. There may still be a role for tissue biopsy in unsolved cases or when the diagnosis is still not clear after NGS studies.

Newborn Screening: Current Status in Alberta, Canada

Newborn screening (NBS) in Alberta is delivered by a number of government and health service entities who work together to provide newborn screening to infants born in Alberta, the Northwest Territories, and the Kitikmeot region of the Nunavut territory. The Alberta panel screens for 21 disorders (16 metabolic, two endocrine, cystic fibrosis, severe combined immunodeficiency, and sickle cell disease). NBS is a standard of care, but is not mandatory. NBS performance is monitored by the Alberta Newborn Metabolic Screening (NMS) Program and NMS Laboratory, who strive for continuous quality improvement. Performance analysis found that over 99% of registered infants in Alberta received a newborn screen and over 98% of these infants received a screen result within 10 days of age.

CCMG practice guideline: laboratory guidelines for next-generation sequencing

PurposeThe purpose of this document is to provide guidance for the use of next-generation sequencing (NGS, also known as massively parallel sequencing or MPS) in Canadian clinical genetic laboratories for detection of genetic variants in genomic DNA and mitochondrial DNA for inherited disorders, as well as somatic variants in tumour DNA for acquired cancers. They are intended for Canadian clinical laboratories engaged in developing, validating and using NGS methods. METHODS OF STATEMENT DEVELOPMENT: The document was drafted by the Canadian College of Medical Geneticists (CCMG) Ad Hoc Working Group on NGS Guidelines to make recommendations relevant to NGS. The statement was circulated for comment to the CCMG Laboratory Practice and Clinical Practice committees, and to the CCMG membership. Following incorporation of feedback, the document was approved by the CCMG Board of Directors. DISCLAIMER: The CCMG is a Canadian organisation responsible for certifying medical geneticists and clinical laboratory geneticists, and for establishing professional and ethical standards for clinical genetics services in Canada. The current CCMG Practice Guidelines were developed as a resource for clinical laboratories in Canada and should not be considered to be inclusive of all information laboratories should consider in the validation and use of NGS for a clinical laboratory service.

The novel p.Ser263Phe mutation in the human high-affinity choline transporter 1 (CHT1/SLC5A7) causes a lethal form of fetal akinesia syndrome

A subset of a larger and heterogeneous class of disorders, the congenital myasthenic syndromes (CMS) are caused by pathogenic variants in genes encoding proteins that support the integrity and function of the neuromuscular junction (NMJ). A central component of the NMJ is the sodium-dependent high-affinity choline transporter 1 (CHT1), a solute carrier protein (gene symbol SLC5A7), responsible for the reuptake of choline into nerve termini has recently been implicated as one of several autosomal recessive causes of CMS. We report the identification and functional characterization of a novel pathogenic variant in SLC5A7, c.788C>T (p.Ser263Phe) in an El Salvadorian family with a lethal form of a congenital myasthenic syndrome characterized by fetal akinesia. This study expands the clinical phenotype and insight into a form of fetal akinesia related to CHT1 defects and proposes a genotype-phenotype correlation for the lethal form of SLC5A7-related disorder with potential implications for genetic counseling.

Hybrid gel electrophoresis using skin fibroblasts to aid in diagnosing mitochondrial disease

Objective

We developed a novel, hybrid method combining both blue-native (BN-PAGE) and clear-native (CN-PAGE) polyacrylamide gel electrophoresis, termed BCN-PAGE, to perform in-gel activity stains on the mitochondrial electron transport chain (ETC) complexes in skin fibroblasts.

Methods

Four patients aged 46–65 years were seen in the Metabolic Clinic at Alberta Children's Hospital and investigated for mitochondrial disease and had BN-PAGE or CN-PAGE on skeletal muscle that showed incomplete assembly of complex V (CV) in each patient. Long-range PCR performed on muscle-extracted DNA identified 4 unique mitochondrial DNA (mtDNA) deletions spanning the ATP6 gene of CV. We developed a BCN-PAGE method in skin fibroblasts taken from the patients at the same time and compared the findings with those in skeletal muscle.

Results

In all 4 cases, BCN-PAGE in skin fibroblasts confirmed the abnormal CV activity found from muscle biopsy, suggesting that the mtDNA deletions involving ATP6 were most likely germline mutations that are associated with a clinical phenotype of mitochondrial disease.

Conclusions

The BCN-PAGE method in skin fibroblasts has a potential to be a less-invasive tool compared with muscle biopsy to screen patients for abnormalities in CV and other mitochondrial ETC complexes.

Plasma-derived cell-free mitochondrial DNA: A novel non-invasive methodology to identify mitochondrial DNA haplogroups in humans

BACKGROUND

Mitochondrial diseases are a clinically heterogeneous group of diseases caused by mutations in either nuclear or mitochondrial DNA (mtDNA). The diagnosis is challenging and has frequently required a tissue biopsy to obtain a sufficient quantity of mtDNA. Less-invasive sources mtDNA, such as peripheral blood leukocytes, urine sediment, or buccal swab, contain a lower quantity of mtDNA compared to tissue sources which may reduce sensitivity. Cellular apoptosis of tissues and hematopoetic cells releases fragments of DNA and mtDNA into the circulation and these molecules can be extracted from plasma as cell-free DNA (cfDNA). However, entire mtDNA has not been successfully identified from the cell free fraction previously. We hypothesized that the circular nature of mtDNA would prevent its degradation and a higher sensitivity method, such as next generation sequencing, could identify intact cf-mtDNA from human plasma.

METHODS

Plasma was obtained from patients with mitochondrial disease diagnosed from skeletal muscle biopsy (n = 7) and healthy controls (n = 7) using a specially cfDNA collection tube (Streck Inc.; La Vista, NE). To demonstrate the presence of mtDNA within these samples, we amplified the isolated DNA using custom PCR primers specific to overlapping fragments of mtDNA. cfDNA samples were then sequenced using the Illumina MiSeq sequencing platform.

RESULTS

We confirmed the presence of mtDNA, demonstrating that the full mitochondrial genome is in fact present within the cell-free plasma fraction of human blood. Sequencing identified the mitochondrial haplogroup matching with the tissue specimen for all patients.

CONCLUSION

We report the existence of full length mtDNA in cell-free human plasma that was successfully used to perform haplogroup matching. Clinical applications for this work include patient monitoring for heteroplasmy status after mitochondrially-targeted therapies or haplogroup monitoring as a measure of stem cell transplantation.

The clinical application of genome-wide sequencing for monogenic diseases in Canada: Position Statement of the Canadian College of Medical Geneticists

Purpose and scope

The aim of this Position Statement is to provide recommendations for Canadian medical geneticists, clinical laboratory geneticists, genetic counsellors and other physicians regarding the use of genome-wide sequencing of germline DNA in the context of clinical genetic diagnosis. This statement has been developed to facilitate the clinical translation and development of best practices for clinical genome-wide sequencing for genetic diagnosis of monogenic diseases in Canada; it does not address the clinical application of this technology in other fields such as molecular investigation of cancer or for population screening of healthy individuals.

Methods of statement development

Two multidisciplinary groups consisting of medical geneticists, clinical laboratory geneticists, genetic counsellors, ethicists, lawyers and genetic researchers were assembled to review existing literature and guidelines on genome-wide sequencing for clinical genetic diagnosis in the context of monogenic diseases, and to make recommendations relevant to the Canadian context. The statement was circulated for comment to the Canadian College of Medical Geneticists (CCMG) membership-at-large and, following incorporation of feedback, approved by the CCMG Board of Directors. The CCMG is a Canadian organisation responsible for certifying medical geneticists and clinical laboratory geneticists, and for establishing professional and ethical standards for clinical genetics services in Canada.

Results and conclusions

Recommendations include (1) clinical genome-wide sequencing is an appropriate approach in the diagnostic assessment of a patient for whom there is suspicion of a significant monogenic disease that is associated with a high degree of genetic heterogeneity, or where specific genetic tests have failed to provide a diagnosis; (2) until the benefits of reporting incidental findings are established, we do not endorse the intentional clinical analysis of disease-associated genes other than those linked to the primary indication; and (3) clinicians should provide genetic counselling and obtain informed consent prior to undertaking clinical genome-wide sequencing. Counselling should include discussion of the limitations of testing, likelihood and implications of diagnosis and incidental findings, and the potential need for further analysis to facilitate clinical interpretation, including studies performed in a research setting. These recommendations will be routinely re-evaluated as knowledge of diagnostic and clinical utility of clinical genome-wide sequencing improves. While the document was developed to direct practice in Canada, the applicability of the statement is broader and will be of interest to clinicians and health jurisdictions internationally.

Discrepant HIV results resolved by human DNA testing

A high-risk patient was informed of a positive HIV antibody/antigen test. However, follow-up samples taken 2-3 months later for HIV RNA and anti-HIV antibodies were negative. Human DNA testing confirmed that all samples were from this patient, excluding a sample mix-up. Laboratory investigations revealed a likely splash-over contamination event.

Defining the role of laboratory genetic counselor

An increasing number of genetic counselors are moving into non-clinical roles, where their primary duties do not involve direct patient contact. According to the National Society of Genetic Counselors Professional Status Survey in 2010, 23% of counselors working in non-clinical roles identified laboratory or genetic testing as their primary area of work. Using a survey, we identified 43 genetic counselors who work predominately in laboratory settings. The two primary tasks performed by participants, include acting as a customer liaison (95%) and calling out test results (88%). Nineteen participants (44.2%) also reported spending a considerable amount of time signing reports. The most prevalent areas of job satisfaction were support from laboratory directors (76.8%), autonomy (76.7%), interactions with clinicians (69.7%) and interaction with other genetics counselors (67.5%). This is the first study specifically looking at the roles of laboratory genetic counselors, which is an expanding area of genetic counseling.

Newborn screening for cystic fibrosis in Alberta: Two years of experience

On April 1, 2007, Alberta became the first province in Canada to introduce cystic fibrosis (CF) to its newborn screening program. The Alberta protocol involves a two-tier algorithm involving an immunoreactive trypsinogen measurement followed by molecular analysis using a CF panel for 39 mutations. Positive screens are followed up with sweat chloride testing and an assessment by a CF specialist. Of the 99,408 newborns screened in Alberta during the first two years of the program, 221 had a positive CF newborn screen. The program subsequently identified and initiated treatment in 31 newborns with CF. A relatively high frequency of the R117H mutation and the M1101K mutation was noted. The M1101K mutation is common in the Hutterite population. The presence of the R117H mutation has created both counselling and management dilemmas. The ability to offer CF transmembrane regulator full sequencing may help resolve diagnostic dilemmas. Counselling and management challenges are created when mutations are mild or of unknown clinical significance.

Increasing rates and clinical consequences of nalidixic acid-resistant isolates causing enteric fever in returned travellers: an 18-year experience

The purpose of this study was to examine the rate and clinical consequences of nalidixic acid-resistant (NAR) isolates in travellers with enteric fever presenting to a hospital in a developed country. We retrospectively examined microbiologically confirmed cases of enteric fever in adult returned travellers over an 18-year period presenting to two tertiary referral hospitals in Melbourne, Australia. There were 59 cases of Salmonella typhi infection, 43 cases of S. paratyphi A infection and two cases of S. paratyphi B infection. Most patients reported recent travel to India (36%) or Indonesia (29%). NAR isolates were commonly encountered (41% of all isolates), particularly from India (75%), Pakistan (80%) and Bangladesh (60%). The number of NAR isolates increased progressively after 2003. Patients with NAR isolates had prolonged mean fever clearance time (5.6 vs. 3.3 days, P = 0.03) and prolonged hospital stay (7.9 vs. 5.7 days, P = 0.02) compared to non-resistant isolates. This represents the largest report of NAR enteric fever in returned travellers. NAR isolates predominate in cases of enteric fever from South Asia and result in prolonged fever clearance time and hospital stay. Empiric therapy with alternative antibiotics such as ceftriaxone or azithromycin should be considered in patients with suspected enteric fever from this region.

Positron emission tomography analysis of [11C]KW-6002 binding to human and rat adenosine A2A receptors in the brain

Adenosine A(2A) receptors are found on striatal neurones projecting to the external pallidum. KW-6002 (istradefylline) is a potent and selective antagonist for the adenosine A(2A) receptors in the CNS and acts to inhibit the excessive activity of this pathway in the MPTP marmoset model of PD, thus relieving parkinsonism. The objectives of this study were to investigate the regional binding of the novel positron emission tomography tracer [(11)C]KW-6002 in the healthy human brain and the rat brain, along with receptor occupancy by cold KW-6002 at varying doses in human. The highest [(11)C]KW-6002 uptake in the rat brain was seen in striatum and lower levels in cortex and cerebellum. Brain [(11)C]KW-6002 uptake was well characterized in humans by a two-tissue compartmental model with a blood volume term, and the ED(50) of cold KW-6002 was 0.5 mg in the striatum. Over 90% receptor occupancy was achieved with daily oral doses of greater than 5 mg. In humans, blockable binding was present in all gray matter structures including the cerebellum, which has not been reported to express A(2A) receptors. MRS 1745, an A(2B) receptor selective antagonist, had no effect on the cerebellar binding of [(11)C]KW-6002 in rats, suggesting that this blockable signal is unlikely to result from an affinity for adenosine A(2B) receptors.

Choosing the right inhaler for patients with asthma

This article assesses the suitability of inhaler devices for patients with asthma according to their individual needs. Three main types of inhalers are discussed: pressurised metered dose inhalers, breath-actuated inhalers and dry powder inhalers. The advantages and disadvantages of these devices are discussed in relation to lifestyle, ability and suitability for individuals.

Effect of 5-HT on binding of [(11)C] WAY 100635 to 5-HT(IA) receptors in rat brain, assessed using in vivo microdialysis nd PET after fenfluramine

By using a combination of positron emission tomography (PET) and postmortem tissue dissection, the effect of increased endogenous serotonin on specific binding of [(11)C]WAY 100635 to the 5-HT(1A) receptor was investigated in rat brain in vivo. The binding studies were complemented by in vivo microdialysis to monitor 5-HT levels in similarly treated isoflurane-anaesthetised rats, with the dialysis probe locations corresponding to two of the tissues sampled for specific binding of the radioligand. Fenfluramine treatment (10 mg/kg i.p.) resulted in a approximately 5-fold increase in extracellular 5-HT in medial prefrontal cortex and a approximately 15-fold increase in lateral hippocampus, maximal at approximately 40 min after injection. PET scan duration was either 60 or 90 min, beginning 30 min after fenfluramine injection. The specific binding of [(11)C]WAY 100635 was reduced by 10-20% in hippocampus, which showed highest binding in control animals. Specific binding, however, was unaffected in both prefrontal cortex and midbrain raphe, each additional high binding regions. The minimal effects are consistent with a low baseline occupancy of the 5-HT(1A) receptor by 5-HT in vivo, so that only a large change in endogenous agonist concentration will affect radioligand binding. This implies that utilisation of [(11)C]WAY 100635 in human PET to quantify 5-HT(1A) receptor expression can be extended to pathology where synaptic 5-HT levels are altered as a consequence of the disease state.

Pindolol occupancy of 5-HT(1A) receptors measured in vivo using small animal positron emission tomography with carbon-11 labeled WAY 100635

Positron emission tomography (PET), following an intravenous injection of [carbonyl-(11)C]WAY 100635, was used to image central 5-HT(1A) receptors in rat following pretreatment with graded doses of (-)-pindolol (0.001-3 mg/kg, i.v.). The use of PET had advantages over ex vivo radioligand binding methods in that it produced parametric image volumes and reduced errors due to inter-rat variability. Time-radioactivity curves from regions of interest (ROI) acquired from individual rats enabled the estimation of specific binding of the radioligand using a compartmental model with reference tissue input. Binding potential (BP) of [(11)C]WAY 100635 was estimated for frontal cortex and hippocampus (postsynaptic), and midbrain raphe nuclei (presynaptic). In the latter ROI, pindolol dose-dependently decreased BP. The saturation curve could be fitted to a single-site model up to the lowest dose of pindolol used, giving an ED(50) (dose to cause 50% occupancy) value of 0.26 +/- 0. 05 mg/kg, and inclusion of control (nonpindolol-treated) rats did not affect the fit. In contrast, in cortex and hippocampus ROI, low doses of pindolol caused an increase in BP compared with controls. Pindolol doses greater than approximately 0.1 mg/kg, resulted in a dose-dependent decrease in BP, and ED(50) values in cortex and hippocampus were estimated as 0.44 +/- 0.13 and 0.48 +/- 0.12 mg/kg, respectively. The increase in [(11)C]WAY 100635 binding at low pindolol doses is feasibly related to a decrease in basal receptor occupancy following reduced release of endogenous 5-HT. Considering the apparently greater potency of pindolol at the midbrain raphe ROI, this effect could be mediated via agonist activity at the autoreceptor.

Radio-imaging in small animals

As the resolution of radio-imaging systems improves, the prospect of in-vivo imaging of small animals becomes more attractive. Purpose-built positron emission tomography (PET) scanners capable of imaging individual tissues within the rat brain are now in routine experimental use and in-vivo tracer and saturation-kinetic studies are now possible. The study of small animals in this way does have intrinsic problems and constraints associated with it. For example, the animal must be completely immobilized, stable ligand within the radiolabelled preparation may be limiting and anatomical definition may be poor. In spite of this, consistent, semi-quantitative data can be produced and in-vivo radio-imaging can provide a genuine and unique complement to more conventional techniques. Animal numbers can be significantly reduced and the quality of data improved due to reduced inter-animal variation, and longitudinal studies, to monitor disease progression, are feasible. As the resolution of imaging systems improves still further, such studies could be extended to mouse, in addition to rat, models of disease.

A longitudinal study of the change in resistance patterns and genetic relationship of oral Candida albicans from HIV-infected patients

Candida albicans is an important opportunistic pathogen in the oral cavity of HIV-infected patients. C. albicans was isolated repeatedly over a period of 30 months from the mouth-swills of five males with category IV HIV infection who suffered from recurrent pseudomembranous oral candidosis and were being treated with fluconazole. C. albicans was identified by the germ tube test, carbon assimilation by the API 20C test (bioMerieux sa, Marcy, l'Etoile, France) and morphology on cornmeal Tween 20 agar. Sensitivity testing was performed with a disk diffusion method using neosensitabs (Rosco Diagnostica, Taasrup, Denmark) and the broth microdilution assay using RPMI 1640 medium. Isolates from the five patients taken between 14 and 30 months apart (mean = 23 months) showed the development of resistance to several antifungal agents, notably fluconazole, miconazole and itraconazole by the disc diffusion method and markedly higher minimum inhibitory concentrations (MICs) for fluconazole by the broth microdilution assay. Genetic relatedness of the C. albicans strains was assessed using the mixed-linker polymerase chain reaction method. Four patients had isolates which were genetically identical, while one patient had isolates of varying genetic type. This study has shown that in HIV-infected patients with recurrent oral pseudomembraneous candidosis, the development of drug resistance to antifungal agents may either be due to increased resistance of a single strain or replacement with a more resistant strain.

A cost-minimization study of cancer patients requiring a narcotic infusion in hospital and at home

We conducted a retrospective, non-randomized, cost-minimization study, from the perspective of the Ministry of Health, to compare the cost of managing cancer patients who required narcotic infusions, in hospital and at home. Our medical costs averaged $369.72 per inpatient day and $150.24 per outpatient day (saving $219.48 per diem, 1988 Canadian dollars), while narcotic costs were the same for any given patient in both settings. Sensitivity analysis showed that no reasonable changes in the quantity and cost of services reduced our savings by more than 50%. During incremental analysis, savings increased as more outpatient days were managed by our centre, from $0.00 for 318 days, to more than $500,000 for over 2000 days per annum. As this program has been extremely cost effective and preferred by our patients, other hospitals and central funding agencies might consider establishing a regional outpatient narcotic infusion program to reduce their costs.