Gamma-Aminobutyric Acid A Receptor Subunit Expression and Cellular Localization in the Human Parkinsonian Globus Pallidus

BACKGROUND

The gamma-aminobutyric acid A (GABA_A) receptor is an important mediator of cellular signaling in the globus pallidus and might be implicated in the pathophysiology of Parkinson disease (PD). The goal of the present study was to characterize GABA_A receptor subunit expression in the normal and parkinsonian human globus pallidus.

METHODS

Postmortem brain specimens were obtained from 8 patients with pathological evidence of PD at autopsy and from 4 control patients without such evidence. These tissues were exposed to primary antibodies directed against the α1 and α3 subunits of the GABA_A receptor and were visualized and quantified using fluorescence microscopy.

RESULTS

No differences were found in the pallidal neuronal density in the control versus PD tissues. Projection neurons strongly expressed the α1, α3, and β2 GABA_A receptor subunits. After normalizing the immunofluorescence intensities in the globus pallidus to those in the adjacent structures, no significant differences were found in GABA_A receptor subunit expression in the globus pallidus between the PD specimens and the control specimens.

CONCLUSIONS

Compensatory changes in GABA_A receptor α1 and α3 subunit expression in response to PD-related signaling abnormalities in the globus pallidus did not occur in our PD cohort.

Untargeted metabolomics and infrared ion spectroscopy identify biomarkers for pyridoxine-dependent epilepsy

BackgroundPyridoxine-dependent epilepsy (PDE-ALDH7A1) is an inborn error of lysine catabolism that presents with refractory epilepsy in newborns. Biallelic ALDH7A1 variants lead to deficiency of α-aminoadipic semialdehyde dehydrogenase/antiquitin, resulting in accumulation of piperideine-6-carboxylate (P6C), and secondary deficiency of the important cofactor pyridoxal-5'-phosphate (PLP, active vitamin B6) through its complexation with P6C. Vitamin B6 supplementation resolves epilepsy in patients, but intellectual disability may still develop. Early diagnosis and treatment, preferably based on newborn screening, could optimize long-term clinical outcome. However, no suitable PDE-ALDH7A1 newborn screening biomarkers are currently available.MethodsWe combined the innovative analytical methods untargeted metabolomics and infrared ion spectroscopy to discover and identify biomarkers in plasma that would allow for PDE-ALDH7A1 diagnosis in newborn screening.ResultsWe identified 2S,6S-/2S,6R-oxopropylpiperidine-2-carboxylic acid (2-OPP) as a PDE-ALDH7A1 biomarker, and confirmed 6-oxopiperidine-2-carboxylic acid (6-oxoPIP) as a biomarker. The suitability of 2-OPP as a potential PDE-ALDH7A1 newborn screening biomarker in dried bloodspots was shown. Additionally, we found that 2-OPP accumulates in brain tissue of patients and Aldh7a1-knockout mice, and induced epilepsy-like behavior in a zebrafish model system.ConclusionThis study has opened the way to newborn screening for PDE-ALDH7A1. We speculate that 2-OPP may contribute to ongoing neurotoxicity, also in treated PDE-ALDH7A1 patients. As 2-OPP formation appears to increase upon ketosis, we emphasize the importance of avoiding catabolism in PDE-ALDH7A1 patients.FundingSociety for Inborn Errors of Metabolism for Netherlands and Belgium (ESN), United for Metabolic Diseases (UMD), Stofwisselkracht, Radboud University, Canadian Institutes of Health Research, Dutch Research Council (NWO), and the European Research Council (ERC).

Pathogenic Variants in CEP85L Cause Sporadic and Familial Posterior Predominant Lissencephaly

Lissencephaly (LIS), denoting a "smooth brain," is characterized by the absence of normal cerebral convolutions with abnormalities of cortical thickness. Pathogenic variants in over 20 genes are associated with LIS. The majority of posterior predominant LIS is caused by pathogenic variants in LIS1 (also known as PAFAH1B1), although a significant fraction remains without a known genetic etiology. We now implicate CEP85L as an important cause of posterior predominant LIS, identifying 13 individuals with rare, heterozygous CEP85L variants, including 2 families with autosomal dominant inheritance. We show that CEP85L is a centrosome protein localizing to the pericentriolar material, and knockdown of Cep85l causes a neuronal migration defect in mice. LIS1 also localizes to the centrosome, suggesting that this organelle is key to the mechanism of posterior predominant LIS.

Reduced neurosteroid potentiation of GABAA receptors in epilepsy and depolarized hippocampal neurons

OBJECTIVE

Neurosteroids regulate neuronal excitability by potentiating γ-aminobutyric acid type-A receptors (GABARs). In animal models of temporal lobe epilepsy, the neurosteroid sensitivity of GABARs is diminished and GABAR subunit composition is altered. We tested whether similar changes occur in patients with epilepsy and if depolarization-induced increases in neuronal activity can replicate this effect.

METHODS

We determined GABAR α4 subunit expression in cortical tissue resected from pediatric epilepsy patients. Modulation of human GABARs by allopregnanolone and Ro15-4513 was measured in Xenopus oocytes using whole-cell patch clamp. To extend the findings obtained using tissue from epilepsy patients, we evaluated GABAR expression and modulation by allopregnanolone and Ro15-4513 in cultured rat hippocampal neurons exposed to high extracellular potassium (HK) to increase neuronal activity.

RESULTS

Expression of α4 subunits was increased in pediatric cortical epilepsy specimens encompassing multiple pathologies. The potentiation of GABA-evoked currents by the neurosteroid allopregnanolone was decreased in Xenopus oocytes expressing GABARs isolated from epilepsy patients. Furthermore, receptors isolated from epilepsy but not control tissue were sensitive to potentiation by Ro15-4513, indicating higher expression of α4 βx γ2 subunit-containing receptors. Correspondingly, increasing the activity of cultured rat hippocampal neurons reduced allopregnanolone potentiation of miniature inhibitory postsynaptic currents (mIPSCs), increased modulation of tonic GABAR current by Ro15-4513, upregulated the surface expression of α4 and γ2 subunits, and increased the colocalization of α4 and γ2 subunit immunoreactivity.

INTERPRETATION

These findings suggest that seizure activity-induced upregulation of α4 βx γ2 subunit-containing GABARs could affect the anticonvulsant actions of neurosteroids.

mTORC2 Steals the Spotlight

Therapeutic Inhibition of mTORC2 Rescues the Behavioral and Neurophysiological Abnormalities Associated With PTEN-Deficiency

Chen C, Sgritta M, Mays J, et al. Nat Med. 2019;25(11):1684-1690. doi:10.1038/s41591-019-0608-y.

Dysregulation of mammalian target of rapamycin (mTOR) signaling, which is mediated by 2 structurally and functionally distinct complexes, mTORC1 and mTORC2, has been implicated in several neurological disorders. Individuals carrying loss-of-function mutations in the phosphatase and tensin homolog (PTEN) gene, a negative regulator of mTOR signaling, are prone to developing macrocephaly, autism spectrum disorder (ASD), seizures, and intellectual disability. It is generally believed that the neurological symptoms associated with loss of PTEN and other mTORopathies (eg, mutations in the tuberous sclerosis genes TSC1 or TSC2) are due to hyperactivation of mTORC1-mediated protein synthesis. Using molecular genetics, we unexpectedly found that genetic deletion of mTORC2 (but not mTORC1) activity prolonged life span, suppressed seizures, rescued ASD-like behaviors and long-term memory, and normalized metabolic changes in the brain of mice lacking Pten. In a more therapeutically oriented approach, we found that administration of an antisense oligonucleotide targeting mTORC2’s defining component Rictor specifically inhibits mTORC2 activity and reverses the behavioral and neurophysiological abnormalities in adolescent Pten-deficient mice. Collectively, our findings indicate that mTORC2 is the major driver underlying the neuropathophysiology associated with Pten-deficiency, and its therapeutic reduction could represent a promising and broadly effective translational therapy for neurological disorders where mTOR signaling is dysregulated.

The Space-Time Continuum of Cortical Dysplasia

Somatic Mutations Activating the mTOR Pathway in Dorsal Telencephalic Progenitors Cause a Continuum of Cortical Dysplasias

D’Gama AM, Woodworth MB, Hossain AA, Bizzotto S, Hatem NE, LaCoursiere CM, Najm I, Ying Z, Yang E, Barkovich AJ, Kwiatkowski DJ, Vinters HV, Madsen JR, Mathern GW, Blümcke I, Poduri A, Walsh CA. Cell Rep. 2017;21:3754-3766. doi:10.1016/j.celrep.2017.11.106

Focal cortical dysplasia (FCD) and hemimegalencephaly (HME) are epileptogenic neurodevelopmental malformations caused by mutations in mTOR pathway genes. Deep sequencing of these genes in FCD/HME brain tissue identified an etiology in 27 (41%) of 66 cases. Radiographically indistinguishable lesions are caused by somatic activating mutations in AKT3, MTOR, and PIK3CA and germline loss-of-function mutations in DEPDC5, NPRL2, and TSC1/2, including TSC2 mutations in isolated HME demonstrating a “two-hit” model. Mutations in the same gene cause a disease continuum from FCD to HME to bilateral brain overgrowth, reflecting the progenitor cell and developmental time when the mutation occurred. Single-cell sequencing demonstrated mTOR activation in neurons in all lesions. Conditional Pik3ca activation in the mouse cortex showed that mTOR activation in excitatory neurons and glia, but not interneurons, is sufficient for abnormal cortical overgrowth. These data suggest that mTOR activation in dorsal telencephalic progenitors, in some cases specifically the excitatory neuron lineage, causes cortical dysplasia.

Association of MTOR Mutations With Developmental Brain Disorders, Including Megalencephaly, Focal Cortical Dysplasia, and Pigmentary Mosaicism

IMPORTANCE

Focal cortical dysplasia (FCD), hemimegalencephaly, and megalencephaly constitute a spectrum of malformations of cortical development with shared neuropathologic features. These disorders are associated with significant childhood morbidity and mortality.

OBJECTIVE

To identify the underlying molecular cause of FCD, hemimegalencephaly, and diffuse megalencephaly.

DESIGN, SETTING, AND PARTICIPANTS

Patients with FCD, hemimegalencephaly, or megalencephaly (mean age, 11.7 years; range, 2-32 years) were recruited from Pediatric Hospital A. Meyer, the University of Hong Kong, and Seattle Children's Research Institute from June 2012 to June 2014. Whole-exome sequencing (WES) was performed on 8 children with FCD or hemimegalencephaly using standard-depth (50-60X) sequencing in peripheral samples (blood, saliva, or skin) from the affected child and their parents and deep (150-180X) sequencing in affected brain tissue. Targeted sequencing and WES were used to screen 93 children with molecularly unexplained diffuse or focal brain overgrowth. Histopathologic and functional assays of phosphatidylinositol 3-kinase-AKT (serine/threonine kinase)-mammalian target of rapamycin (mTOR) pathway activity in resected brain tissue and cultured neurons were performed to validate mutations.

MAIN OUTCOMES AND MEASURES

Whole-exome sequencing and targeted sequencing identified variants associated with this spectrum of developmental brain disorders.

RESULTS

Low-level mosaic mutations of MTOR were identified in brain tissue in 4 children with FCD type 2a with alternative allele fractions ranging from 0.012 to 0.086. Intermediate-level mosaic mutation of MTOR (p.Thr1977Ile) was also identified in 3 unrelated children with diffuse megalencephaly and pigmentary mosaicism in skin. Finally, a constitutional de novo mutation of MTOR (p.Glu1799Lys) was identified in 3 unrelated children with diffuse megalencephaly and intellectual disability. Molecular and functional analysis in 2 children with FCD2a from whom multiple affected brain tissue samples were available revealed a mutation gradient with an epicenter in the most epileptogenic area. When expressed in cultured neurons, all MTOR mutations identified here drive constitutive activation of mTOR complex 1 and enlarged neuronal size.

CONCLUSIONS AND RELEVANCE

In this study, mutations of MTOR were associated with a spectrum of brain overgrowth phenotypes extending from FCD type 2a to diffuse megalencephaly, distinguished by different mutations and levels of mosaicism. These mutations may be sufficient to cause cellular hypertrophy in cultured neurons and may provide a demonstration of the pattern of mosaicism in brain and substantiate the link between mosaic mutations of MTOR and pigmentary mosaicism in skin.

Review of Commercially Available Epilepsy Genetic Panels

Next generation sequencing panels have revolutionized the diagnostic approach to patients with epilepsy. There are several commercial epilepsy panels available. We assessed the list of genes tested and consent forms for epilepsy panels available at seven laboratories. The panels varied in the number of genes included (70-465 genes). In some panels, genes not currently associated with epilepsy were included (up to 4 % of panel content). The panels also included genes for lysosomal storage disorders (6-12 %), congenital disorders of glycosylation (0-8.5 %), metabolic disorders (3.5-34 %), neurological syndromes (18-43 %) and multisystemic genetic syndromes (6.4-21 %). Informed consents differed significantly between laboratories ranging from basic information about genetic testing and possible results to information about insurance, genetic counseling and familial testing, and incidental findings.Our findings suggest that it is important to consider the range of genes offered on epilepsy panels and their predicted phenotypes in an effort toward improving the informed consent process.

PI3K/AKT pathway mutations cause a spectrum of brain malformations from megalencephaly to focal cortical dysplasia

Malformations of cortical development containing dysplastic neuronal and glial elements, including hemimegalencephaly and focal cortical dysplasia, are common causes of intractable paediatric epilepsy. In this study we performed multiplex targeted sequencing of 10 genes in the PI3K/AKT pathway on brain tissue from 33 children who underwent surgical resection of dysplastic cortex for the treatment of intractable epilepsy. Sequencing results were correlated with clinical, imaging, pathological and immunohistological phenotypes. We identified mosaic activating mutations in PIK3CA and AKT3 in this cohort, including cancer-associated hotspot PIK3CA mutations in dysplastic megalencephaly, hemimegalencephaly, and focal cortical dysplasia type IIa. In addition, a germline PTEN mutation was identified in a male with hemimegalencephaly but no peripheral manifestations of the PTEN hamartoma tumour syndrome. A spectrum of clinical, imaging and pathological abnormalities was found in this cohort. While patients with more severe brain imaging abnormalities and systemic manifestations were more likely to have detected mutations, routine histopathological studies did not predict mutation status. In addition, elevated levels of phosphorylated S6 ribosomal protein were identified in both neurons and astrocytes of all hemimegalencephaly and focal cortical dysplasia type II specimens, regardless of the presence or absence of detected PI3K/AKT pathway mutations. In contrast, expression patterns of the T308 and S473 phosphorylated forms of AKT and in vitro AKT kinase activities discriminated between mutation-positive dysplasia cortex, mutation-negative dysplasia cortex, and non-dysplasia epilepsy cortex. Our findings identify PI3K/AKT pathway mutations as an important cause of epileptogenic brain malformations and establish megalencephaly, hemimegalencephaly, and focal cortical dysplasia as part of a single pathogenic spectrum.

Novel mutations in ATP1A3 associated with catastrophic early life epilepsy, episodic prolonged apnea, and postnatal microcephaly

OBJECTIVE

Mutations of ATP1A3 have been associated with rapid onset dystonia-parkinsonism and more recently with alternating hemiplegia of childhood. Here we report one child with catastrophic early life epilepsy and shortened survival, and another with epilepsy, episodic prolonged apnea, postnatal microcephaly, and severe developmental disability. Novel heterozygous mutations (p.Gly358Val and p.Ile363Asn) were identified in ATP1A3 in these children.

METHODS

Subjects underwent next-generation sequencing under a research protocol. Clinical data were collected retrospectively. The biochemical effects of the mutations on ATP1A3 protein function were investigated. Postmortem neuropathologic specimens from control and affected subjects were studied.

RESULTS

The mutations localized to the P domain of the Na,K-ATPase α3 protein, and resulted in significant reduction of Na,K-ATPase activity in vitro. We demonstrate in both control human brain tissue and that from the subject with the p.Gly358Val mutation that ATP1A3 immunofluorescence is prominently associated with interneurons in the cortex, which may provide some insight into the pathogenesis of the disease.

SIGNIFICANCE

The findings indicate these mutations cause severe phenotypes of ATP1A3-related disorder spectrum that include catastrophic early life epilepsy, episodic apnea, and postnatal microcephaly.

Breast size and breast cancer: a systematic review

BACKGROUND

There are many known breast cancer risk factors, but traditionally the list has not included breast size. The aim of this study was to synthesize the literature on breast size as a risk factor for breast carcinoma by examining studies addressing this question both directly and indirectly.

METHODS

A systematic review was performed searching MEDLINE from 1950 to November 2010, and updated again in February 2014. Literature was sought to assess the relationship between the following variables and breast cancer: 1) breast size; 2) breast reduction; 3) breast augmentation; and 4) prophylactic subcutaneous mastectomy. Findings were summarized and the levels of evidence were assessed.

RESULTS

50 papers were included in the systematic review. Increasing breast size appears to be a risk factor for breast cancer, but studies are limited by their retrospective nature, imperfect size measurement techniques and confounding variables. The evidence is stronger for risk reduction with breast reduction, including prophylactic subcutaneous mastectomy at the extreme. Generally the breast augmentation population has a lower risk of breast cancer than the general population, but it is unclear whether or not this is related to the bias of small breasts in this patient population and the presence of other confounders.

CONCLUSIONS

There is direct and indirect evidence that breast size is an important factor in the risk of developing breast cancer. Plastic surgeons are in a unique position to observe this effect. Well-designed prospective studies are required to further assess this risk factor.

Glial localization of antiquitin: implications for pyridoxine-dependent epilepsy

OBJECTIVE

A high incidence of structural brain abnormalities has been reported in individuals with pyridoxine-dependent epilepsy (PDE). PDE is caused by mutations in ALDH7A1, also known as antiquitin. How antiquitin dysfunction leads to cerebral dysgenesis is unknown. In this study, we analyzed tissue from a child with PDE as well as control human and murine brain to determine the normal distribution of antiquitin, its distribution in PDE, and associated brain malformations.

METHODS

Formalin-fixed human brain sections were subjected to histopathology and fluorescence immunohistochemistry studies. Frozen brain tissue was utilized for measurement of PDE-associated metabolites and Western blot analysis. Comparative studies of antiquitin distribution were performed in developing mouse brain sections.

RESULTS

Histologic analysis of PDE cortex revealed areas of abnormal radial neuronal organization consistent with type Ia focal cortical dysplasia. Heterotopic neurons were identified in subcortical white matter, as was cortical astrogliosis, hippocampal sclerosis, and status marmoratus of the basal ganglia. Highly elevated levels of lysine metabolites were present in postmortem PDE cortex. In control human and developing mouse brain, antiquitin immunofluorescence was identified in radial glia, mature astrocytes, ependyma, and choroid plexus epithelium, but not in neurons. In PDE cortex, antiquitin immunofluorescence was greatly attenuated with evidence of perinuclear accumulation in astrocytes.

INTERPRETATION

Antiquitin is expressed within glial cells in the brain, and its dysfunction in PDE is associated with neuronal migration abnormalities and other structural brain defects. These malformations persist despite postnatal pyridoxine supplementation and likely contribute to neurodevelopmental impairments.

Correlations in timing of sodium channel expression, epilepsy, and sudden death in Dravet syndrome

Dravet Syndrome (DS) is an intractable genetic epilepsy caused by loss-of-function mutations in SCN1A, the gene encoding brain sodium channel Nav 1.1. DS is associated with increased frequency of sudden unexpected death in humans and in a mouse genetic model of this disease. Here we correlate the time course of declining expression of the murine embryonic sodium channel Nav 1.3 and the rise in expression of the adult sodium channel Nav 1.1 with susceptibility to epileptic seizures and increased incidence of sudden death in DS mice. Parallel studies with unaffected human brain tissue demonstrate similar decline in Nav 1.3 and increase in Nav 1.1 with age. In light of these results, we introduce the hypothesis that the natural loss Nav 1.3 channel expression in brain development, coupled with the failure of increase in functional Nav 1.1 channels in DS, defines a tipping point that leads to disinhibition of neural circuits, intractable seizures, co-morbidities, and premature death in this disease.

Tissue localization during resective epilepsy surgery

Object

Imaging-guided surgery (IGS) systems are widely used in neurosurgical practice. During epilepsy surgery, the authors routinely use IGS landmarks to localize intracranial electrodes and/or specific brain regions. The authors have developed a technique to coregister these landmarks with pre- and postoperative scans and the Montreal Neurological Institute (MNI) standard space brain MRI to allow 1) localization and identification of tissue anatomy; and 2) identification of Brodmann areas (BAs) of the tissue resected during epilepsy surgery. Tracking tissue in this fashion allows for better correlation of patient outcome to clinical factors, functional neuroimaging findings, and pathological characteristics and molecular studies of resected tissue.

Methods

Tissue samples were collected in 21 patients. Coordinates from intraoperative tissue localization were downloaded from the IGS system and transformed into patient space, as defined by preoperative high-resolution T1-weighted MRI volume. Tissue landmarks in patient space were then transformed into MNI standard space for identification of the BAs of the tissue samples.

Results

Anatomical locations of resected tissue were identified from the intraoperative resection landmarks. The BAs were identified for 17 of the 21 patients. The remaining patients had abnormal brain anatomy that could not be meaningfully coregistered with the MNI standard brain without causing extensive distortion.

Conclusions

This coregistration and landmark tracking technique allows localization of tissue that is resected from patients with epilepsy and identification of the BAs for each resected region. The ability to perform tissue localization allows investigators to relate preoperative, intraoperative, and postoperative functional and anatomical brain imaging to better understand patient outcomes, improve patient safety, and aid in research.

Somatic mosaicism in Menkes disease suggests choroid plexus-mediated copper transport to the developing brain

The primary mechanism of copper transport to the brain is unknown, although this process is drastically impaired in Menkes disease, an X-linked neurodevelopmental disorder caused by mutations in an evolutionarily conserved copper transporter, ATP7A. Potential central nervous system entry routes for copper include brain capillary endothelial cells that originate from mesodermal angioblasts and form the blood-brain barrier, and the choroid plexuses, which derive from embryonic ectoderm, and form the blood-cerebrospinal fluid barrier. We exploited a rare (and first reported) example of somatic mosaicism for an ATP7A mutation to shed light on questions about copper transport into the developing brain. In a 20-month-old Menkes disease patient evaluated before copper treatment, blood copper, and catecholamine concentrations were normal, whereas levels in cerebrospinal fluid were abnormal and consistent with his neurologically severe phenotype. We documented disparate levels of mosaicism for an ATP7A missense mutation, P1001L, in tissues derived from different embryonic origins; allele quantitation showed P1001L in approximately 27% of DNA samples from blood cells (mesoderm-derived) and 88% from cultured fibroblasts (ectoderm-derived). These findings imply that the P1001L mutation in the patient preceded formation of the three primary embryonic lineages at gastrulation, with the ectoderm layer ultimately harboring a higher percentage of mutation-bearing cells than mesoderm or endoderm. Since choroid plexus epithelia are derived from neuroectoderm, and brain capillary endothelial cells from mesodermal angioblasts, the clinical and biochemical findings in this infant support a critical role for the blood-CSF barrier (choroid plexus epithelia) in copper entry to the developing brain.

Altered GABA(A) receptor subunit expression and pharmacology in human Angelman syndrome cortex

The neurodevelopmental disorder Angelman syndrome is most frequently caused by deletion of the maternally derived chromosome 15q11-q13 region, which includes not only the causative UBE3A gene, but also the beta(3)-alpha(5)-gamma(3) GABA(A) receptor subunit gene cluster. GABAergic dysfunction has been hypothesized to contribute to the occurrence of epilepsy and cognitive and behavioral impairments in this condition. In the present study, analysis of GABA(A) receptor subunit expression and pharmacology was performed in cerebral cortex from four subjects with Angelman syndrome and compared to that from control tissue. The membrane fraction of frozen postmortem neocortical tissue was isolated and subjected to quantitative Western blot analysis. The ratios of beta(3)/beta(2) and alpha(5)/alpha(1) subunit protein expression in Angelman syndrome cortex were significantly decreased when compared with controls. An additional membrane fraction was injected into Xenopus oocytes, resulting in incorporation of the brain membrane vesicles with their associated receptors into the oocyte cellular membrane. Two-electrode voltage-clamp analysis of GABA(A) receptor currents was then performed. Studies of GABA(A) receptor pharmacology in Angelman syndrome cortex revealed increased current enhancement by the alpha(1)-selective benzodiazepine-site agonist zolpidem and by the barbiturate phenobarbital, while sensitivity to current inhibition by zinc was decreased. GABA(A) receptor affinity and modulation by neurosteroids were unchanged. This shift in GABA(A) receptor subunit expression and pharmacology in Angelman syndrome is consistent with impaired extrasynaptic but intact to augmented synaptic cortical GABAergic inhibition, which could contribute to the epileptic, behavioral, and cognitive phenotypes of the disorder.

Impaired maturation of cortical GABA(A) receptor expression in pediatric epilepsy

PURPOSE

Expression of the protein subunits that make up the γ-aminobutyric acid (GABA)(A) receptor pentamer is known to change during postnatal brain development in animal models. In the present study, analysis of cortical GABA(A) subunit expression was performed in control human tissue obtained from infancy through adolescence, and was compared to that from similarly aged children with intractable focal epilepsy.

METHODS

Twenty frozen pediatric control and 25 epileptic neocortical specimens were collected. The membrane fractions were isolated and subjected to quantitative western blot analysis. Subunit expression was correlated with clinical factors including age, pathology, and medication exposure.

RESULTS

In control cortical samples, α₁ and γ₂ GABA(A) receptor subunits exhibited low expression in infancy, which increased over the first several years of life and then stabilized through adolescence. In contrast, α₄ subunit expression was higher in infants than in older children. The level of the chloride transporter KCC2 increased markedly with age, whereas that of NKCC1 decreased. These patterns were absent in the children with epilepsy, both in those with focal cortical dysplasia and in those with cortical gliosis. Although there was marked variability in GABA(A) receptor subunit expression among the children with epilepsy, identifiable patterns of subunit expression were found in each individual child.

DISCUSSION

Maturation of cortical GABA(A) receptor subunit expression continues over the first several years of postnatal human development. Intractable focal epilepsy in children is associated with disruption of this normal developmental pattern. These findings have significant implications for the treatment of children with medications that modulate GABA(A) receptor function.

Ascribing intentions in clinical decision-making

BACKGROUND

The intentions of clinicians are widely considered to be relevant to the ethical assessment of their actions. A better understanding of the psychological factors that influence the ascription of intentions in clinical practice is important for improving the self-understanding of clinical decision-making and, ultimately, the ethics of clinical care. Drawing on empirical research on intentionality that has been done in other contexts, this is the first study to test whether the "asymmetric effect" of intention ascription is exhibited by respondents when presented with clinical decision-making scenarios.

OBJECTIVE

To assess how individuals attribute intentions to clinical actors in clinical decision-making scenarios.

METHODS

A total of 149 first and second year medical students was randomly assigned to two groups (group A, group B). Subjects in each group read two scenarios and submitted anonymous responses to questions regarding each scenario.

RESULTS

The asymmetric effect was strongly exhibited by the responses given to scenario 2, but it was not exhibited by the responses given to scenario 1.

CONCLUSION

The present study provided evidence for the view that people's ascription of intentions to others is influenced by their previous evaluative judgement of the conduct in question.

GABA(A) receptor properties in catastrophic infantile epilepsy

Catastrophic epilepsy due to cortical dysplasia is often intractable to anticonvulsant treatment. Many of the medications used unsuccessfully in treating this disorder are thought to exert at least a portion of their action through enhancement of inhibitory GABA(A) neurotransmission. In the present study, GABA(A) receptor properties in resected brain tissue from four infants with infantile spasms and intractable epilepsy due to cortical dysplasia were measured to determine if this clinical resistance to pharmacologic treatment correlates with alterations in receptor function. Results from epileptic cortex were compared with those from autopsy control samples. To perform these studies, we utilized the technique of injection of brain cellular membrane preparations into the Xenopus oocyte, which results in the incorporation of human GABA(A) receptors in their native configuration into the oocyte plasma membrane. Two-electrode voltage-clamp electrophysiology analysis was then performed to assess GABA(A) receptor pharmacologic properties. The intrinsic properties of affinity, reversal potential, current decay, and current rundown were unchanged in the epileptic infants. Current enhancement by benzodiazepines was also unaltered, as was the response to barbiturates. However, a significant decrease was found in the degree of GABA(A) current enhancement by neurosteroids in the epileptic infants, along with an increase in current inhibition by zinc. These findings may contribute to the mechanisms of intractability in catastrophic infantile epilepsy due to cortical dysplasia, and suggest alternative therapeutic approaches.

Abnormal glutamate homeostasis and impaired synaptic plasticity and learning in a mouse model of tuberous sclerosis complex

Mice with inactivation of the Tuberous sclerosis complex-1 (Tsc1) gene in glia (Tsc1 GFAP CKO mice) have deficient astrocyte glutamate transporters and develop seizures, suggesting that abnormal glutamate homeostasis contributes to neurological abnormalities in these mice. We examined the hypothesis that Tsc1 GFAP CKO mice have elevated extracellular brain glutamate levels that may cause neuronal death, abnormal glutamatergic synaptic function, and associated impairments in behavioral learning. In vivo microdialysis documented elevated glutamate levels in hippocampi of Tsc1 GFAP CKO mice and several cell death assays demonstrated neuronal death in hippocampus and neocortex. Impairment of long-term potentiation (LTP) with tetanic stimulation was observed in hippocampal slices from Tsc1 GFAP CKO mice and was reversed by low concentrations of NMDA antagonist, indicating that excessive synaptic glutamate directly inhibited LTP. Finally, Tsc1 GFAP CKO mice exhibited deficits in two hippocampal-dependent learning paradigms. These results suggest that abnormal glutamate homeostasis predisposes to excitotoxic cell death, impaired synaptic plasticity and learning deficits in Tsc1 GFAP CKO mice.

Epileptogenesis and reduced inward rectifier potassium current in tuberous sclerosis complex-1-deficient astrocytes

PURPOSE

Individuals with tuberous sclerosis complex (TSC) frequently have intractable epilepsy. To gain insights into mechanisms of epileptogenesis in TSC, we previously developed a mouse model of TSC with conditional inactivation of the Tsc1 gene in glia (Tsc1(GFAP)CKO mice). These mice develop progressive seizures, suggesting that glial dysfunction may be involved in epileptogenesis in TSC. Here, we investigated the hypothesis that impairment of potassium uptake through astrocyte inward rectifier potassium (Kir) channels may contribute to epileptogenesis in Tsc1(GFAP)CKO mice.

METHODS

Kir channel function and expression were examined in cultured Tsc1-deficient astrocytes. Kir mRNA expression was analyzed in astrocytes microdissected from neocortical sections of Tsc1(GFAP)CKO mice. Physiological assays of astrocyte Kir currents and susceptibility to epileptiform activity induced by increased extracellular potassium were further studied in situ in hippocampal slices.

RESULTS

Cultured Tsc1-deficient astrocytes exhibited reduced Kir currents and decreased expression of specific Kir channel protein subunits, Kir2.1 and Kir6.1. mRNA expression of the same Kir subunits also was reduced in astrocytes from neocortex of Tsc1(GFAP)CKO mice. By using pharmacologic modulators of signalling pathways implicated in TSC, we showed that the impairment in Kir channel function was not affected by rapamycin inhibition of the mTOR/S6K pathway, but was reversed by decreasing CDK2 activity with roscovitine or retinoic acid. Last, hippocampal slices from Tsc1(GFAP)CKO mice exhibited decreased astrocytic Kir currents, as well as increased susceptibility to potassium-induced epileptiform activity.

CONCLUSIONS

Impaired extracellular potassium uptake by astrocytes through Kir channels may contribute to neuronal hyperexcitability and epileptogenesis in a mouse model of TSC.

HIV exceptionalism, CD4+ cell testing, and conscientious subversion

In recent years, many states in the United States have passed legislation requiring laboratories to report the names of patients with low CD4 cell counts to their state Departments of Health. This name reporting is an integral part of the growing number of "HIV Reporting and Partner Notification Laws" which have emerged in response to recently revised guidelines suggested by the National Centers for Disease Control (CDC). Name reporting for patients with low CD4 cell counts allows for a more accurate tracking of the natural history of HIV disease. However, given that this test is now considered to be an "indicator" of HIV, should it be subject to the same strict consent required for HIV testing? While the CDC has recommended that each state develop its own consent requirements for CD4 cell testing, most states have continued to rely on the presumed consent standards for CD4 cell testing that were in place before the passage of name reporting statutes. This allows physicians who treat patients who refuse HIV testing to order a CD4 cell blood analysis to gather information that is indicative of their patient's HIV status. This paper examines the ethical and legal issues associated with the practice of "conscientious subversion" as it arises when clinicians use CD4 cell counts as a surrogate for HIV testing.

Impaired glial glutamate transport in a mouse tuberous sclerosis epilepsy model

Excessive astrocytosis in cortical tubers in tuberous sclerosis complex (TSC) suggests that astrocytes may be important for epileptogenesis in TSC. We previously demonstrated that astrocyte-specific Tsc1 gene inactivation in mice (Tsc1 cKO mice) results in progressive epilepsy. Here, we report that glutamate transporter expression and function is impaired in Tsc1 cKO astrocytes. Tsc1 cKO mice exhibit decreased GLT-1 and GLAST protein expression. Electrophysiological assays demonstrate a functional decrease in glutamate transport currents of Tsc1 cKO astrocytes in hippocampal slices and astrocyte cultures. These findings suggest that Tsc1 inactivation in astrocytes causes dysfunctional glutamate homeostasis, leading to seizure development in TSC.

Satisfaction With Epidural and Intravenous Patient-Controlled Analgesia

OBJECTIVE

Postoperative intravenous (i.v.) versus epidural morphine patient-controlled analgesia (PCA) were compared regarding maintenance of initial PCA route, pain levels, side effects, and levels of satisfaction. Additionally, the role of preoperative attitudinal expectations in predicting postoperative levels of satisfaction with pain management as well as maintenance of initial PCA route was evaluated.

DESIGN

After either abdominal or thoracic surgery, 70 eligible patients were randomized to receive morphine either through an epidural route (n = 37) or an intravenous PCA pump (n = 33).

SETTING

A large tertiary university teaching hospital in a major northeastern city.

OUTCOME MEASURES

Patients completed visual analogue rating scales 1 week before surgery regarding attitudes such as expectations of satisfaction with pain management after surgery and expectations of medication efficacy postsurgically. Postoperatively, beginning the day after surgery, patients were asked to complete visual analogue rating scales every 12 hours until they were discharged, for a maximum of 3 postoperative days. The scales evaluated included pain, ability to think, and satisfaction with pain control.

RESULTS

There were no significant between-group differences on the postoperative visual analogue scales. Although the overall rate of changing the initial PCA route to which the patients were randomized was identical for both groups (30%), those patients who had thoracic surgery changed their route of PCA administration significantly less when their initial PCA route was epidural (20%) than when their initial PCA route was i.v. (46%) (P <.05). Patients who were satisfied with pain control postoperatively were more likely to have been started on i.v. PCA (P =.001), have lower preoperative expectations of postoperative satisfaction with pain (P <.001), and have higher preoperative expectations of medication effects on postoperative pain (P <.001). Additionally, older patients (P =.007) and patients with lower preoperative expectations of postoperative satisfaction with pain (P =.003) were more likely to adhere to their initial treatment protocol.

CONCLUSIONS

Both techniques, i.v. and epidural PCA, result in high levels of satisfaction. Satisfaction with PCA can be accurately predicted in nearly three of four patients based on initial PCA route and preoperative attitudes. Additionally, maintaining the initial treatment plan can be accurately predicted based on age and preoperative attitudes. Patient expectations about pain relief should be addressed preoperatively, particularly with younger patients, for optimal results.

The ethics of preadoption genetic testing

Developments in genetic technologies have greatly increased our ability to test for a wide variety of genetic disorders in children. These developments raise important ethical questions about the proper use of genetic testing. One context, in particular, where these questions have arisen is that of preadoption genetic testing. This article examines the current consensus view recently advanced by the American College of Medical Genetics and The American Society of Human Genetics on when pediatric testing is ethically permissible. We argue that the consensus view does not adequately recognize the special ethical responsibilities that arise in the preadoption context. Once these special ethical responsibilities are identified, they provide a compelling argument to revise the current standards to permit more preadoption genetic testing than is currently recommended.

Deliberative decision making and the treatment of pain

In recent years, increased emphasis has been placed on the ethical duty of physicians to relieve pain and suffering. According to a 1992 report from The Agency for Health Care Policy Research (AHCPR), the "ethical obligation to manage pain and relieve the patient's suffering is at the core of a health care professional's commitment." However, despite the increased emphasis on the ethical duty to relieve pain, the undertreatment of pain continues to be a serious problem. This problem has been widely discussed, but so far efforts to respond to it have focused almost exclusively on institutional and educational solutions. Yet surprisingly in this discussion very little attention has been paid to articulating a constructive role for the patient in combating this problem. In this article I argue that adequate pain treatment will often require the active participation of the patient in the decision making process. Given the special nature of pain and the special problems that arise in the treatment of pain, adequate pain treatment requires that physicians and patients realize a particular model of shared decision making--one that I refer to as deliberative decision making. As will become clear, my defense of this model is limited to the context of pain management and may not apply in other clinical contexts.

Patient confidentiality and the surrogate's right to know

Physicians treating newly incapacitated patients often must navigate surrogate decision-makers through a difficult course of treatment decisions. Such a process can be complex. Physicians must not only explain the medical facts and prognosis to the surrogate, but also attempt to ensure that the surrogate arrives at decisions that are consistent with the patient's own values and wishes. Where these values and wishes are unknown, physicians must help surrogates make decisions that reflect the patient's best interests.

The virtues in their place: virtue ethics in medicine

We are currently in the midst of a revival of interest in the virtues. A number of contemporary moral philosophers have defended a virtue-based approach to ethics. But does this renewal of interest in the virtues have much to contribute to medical ethics and medical practice? This paper critically discusses this question. It considers and rejects a number of important arguments that purport to establish the significance of the virtues for medical practice. Against these arguments, the paper seeks to show that while the virtues have a genuine role to play in medical ethics, it is a limited role, one that is subordinate to the role that other moral concepts such as rules and principles play.

A novel sensitive method to detect frameshift mutations in exonic repeat sequences of cancer-related genes

We have investigated frameshift mutations in exonic repeats in the ATR, BRCA1, BRCA2, PTCH, CTCF, Cx26, NuMa and TGFbetaRII genes, using human tumor samples from stomach, esophagus, breast and skin and melanoma, as well as colon cancer and endometrial cancer cell lines (125 samples in total). We developed a sensitive method to detect mutations in the repeats, using the introduction of an artificial restriction site into a repeat. The method detects a single mutant among 10(3) normal genes. Thus, an alteration in a repeated sequence can be detected unambiguously. The (A)(8) repeat of BRCA2 was found mutated in only two of five colon cell lines with microsatellite instability (MI(+)). The ATR gene has an (A)(10) repeat which was altered in two of three MI(+) stomach cancer samples and one of three MI(+) endometrial cell lines. The TGFbetaRII gene [with an (A)(10) repeat] had the maximal frequency of mutations: 10 out of 13 MI(+) samples. At least one sample from all types of cancers, except melanomas, was positive for TGFbetaRII gene mutations. No mutations were found in repeats in the BRCA1, PTCH, CTCF, NuMA and Cx26 genes in any types of tumors examined. In conclusion, our study indicates that repeats were altered only in MI(+) cells and that the mutation frequencies in the genes studied differ among tumor types. Based on these results, we discuss meaningful and meaningless alterations in exonic repeats.

Familial cylindromatosis mimicking tuberous sclerosis complex and confirmation of the cylindromatosis locus, CYLD1, in a large family

A large Dutch family had been known for many years to be affected with skin tumours labelled as adenoma sebaceum, which were inherited in an autosomal dominant fashion. Since this skin sign is considered pathognomonic for tuberous sclerosis complex, the condition in the family was labelled accordingly, in the absence of further clinical features of tuberous sclerosis complex-like mental retardation or epilepsy. The skin changes started at early puberty with small eruptions around the nose and progressed to larger tumours, with considerable variation in severity. Some affected members had required plastic surgical reconstruction following excision. Linkage analysis in this family was performed for the two chromosomal regions involved in tuberous sclerosis complex on chromosomes 9q34 and 16p13, but no positive linkage was found. On critical re-evaluation of the clinical and pathological data and renewed assessment, the working diagnosis was changed to autosomal dominant cylindromatosis. The recently published candidate region for cylindromatosis on chromosome 16q12-13 was subsequently proven to be positively linked with a lod score of 3.02 with marker D16S308. Review of pathological specimens confirmed the diagnosis of cylindromatosis. DNA analysis of tumour tissue showed loss of heterozygosity for the cylindromatosis CYLD1 locus. These results confirm the candidate locus for cylindromatosis on chromosome 16q12-13.

The role of calcium in the tumor promoter-induced inhibition of gap junctional intercellular communication

The effect of several tumor promoters (12-O-tetradecanoyl-phorbol-13-acetate (TPA); 1,1'-(2,2,2-trichloroethylidene)bis[4-chlorobenzene] (DDT); Aroclor1260, and clofibrate) on the inhibition of gap junctional intercellular communication (GJIC) and intracellular calcium concentration ([Ca(2+)](i)) was studied in a cell line consisting of initiated cells (3PC). In addition, the effect of different extracellular calcium concentrations ([Ca(2+)](e)) on the effects of tumor promoters on both GJIC and [Ca(2+)](i) were studied. Agents with GJIC inhibiting capacity increased [Ca(2+)](i). However, the increase of [Ca(2+)](i) did not (always) precede GJIC inhibition. The effect of tumor promoters on GJIC were similar under low (0.05 mM) and high (1.20 mM) Ca(2+)(e) conditions, while different effects on [Ca(2+)](i) were found. These results suggest that tumor promoters can inhibit GJIC and change [Ca(2+)](i), but that there is no direct relationship between these two processes.

Differences in the calcium-mediated regulation of gap junctional intercellular communication between a cell line consisting of initiated cells and a carcinoma-derived cell line

Differences in calcium-mediated regulation of gap junctional intercellular communication (GJIC) between a cell line consisting of mouse epidermal initiated cells (3PC) and a mouse epidermal carcinoma-derived cell line (CA3/7) were studied. Under low extracellular calcium ((Ca2+)e) conditions (0.05 mM) CA3/7 cells showed a low level of GJIC compared with 3PC cells. High (Ca2+)e (1.20 mM) raised GJIC between CA3/7 cells to the GJIC level of 3PC cells, which in turn remained unchanged under these conditions. Raising the free intracellular calcium concentration ((Ca2+)i), using a calcium ionophore (ionomycin) or the Ca2+-ATPase inhibitor thapsigargin under low (Ca2+)e conditions, did not affect the GJIC level between 3PC cells, and increased GJIC between CA3/7 cells. Intracellular calcium chelation in 3PC cells under low (Ca2+)e conditions by ethylene glycol-bis(beta-amino-ethyl ether) N,N,N',N'-tetra-acetic acid acetoxy-methyl ester (EGTA-AM) decreased GJIC in this cell line. High (Ca2+)e conditions protected both cell lines from a decreased GJIC by EGTA-AM exposure. Inhibition of calmodulin (CaM) by calmidazolium (CDZ) or N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide (W-7) under low (Ca2+)e conditions, inhibited GJIC in 3PC cells and increased GJIC in CA3/7 cells. Inhibition of Ca2+/CaM-dependent protein kinase (Ca2+/CaM-PK) by 1-(5-iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine (ML-7) decreased GJIC in both cell lines. Western analysis showed that Cx43 was more phosphorylated in both cell lines in concurrence with different effects on the GJIC level. Under conditions in which GJIC was inhibited, a decreased immunostaining of Cx43 on the plasma membrane was found. The level of immunostaining of the cell adhesion molecule E-cadherin on the plasma membranes of both cell types remained unchanged under conditions in which GJIC was changed by modulaters of (Ca2+)i, CaM activity, or the Ca2+/CaM-PK activity. These results indicate that differences exist between 3PC cells and CA3/7 cells in the GJIC regulation by intracellular calcium and calmodulin.

Inhibition of gap junctional intercellular communication and delocalization of the cell adhesion molecule E-cadherin by tumor promoters

The effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) and benzoyl peroxide (BoP) on gap junctional intercellular communication (GJIC) and the amount and localization of E-cadherin was studied in initiated mouse epidermal cells (3PC) and in carcinoma cells (CA3/7) originating from the same cell type. In addition, the localization and phosphorylation of connexin43 was studied in both cell lines and in primary keratinocytes. GJIC inhibition by TPA and BoP was stronger in primary keratinocytes compared with both cell lines. BoP strongly decreased the amount of E-cadherin protein and the level occurring in the membranes in both cell lines, whereas TPA caused a translocation of E-cadherin from the membrane towards the cytosol, without decreasing the total amount of E-cadherin present. The effect of both tumor promoters on connexin43 phosphorylation and localization was agent as well as cell dependent. These results show for the first time that tumor promoters can decrease the quantity and membrane localization of E-cadherin in different cell types.

Glycoalkaloids selectively permeabilize cholesterol containing biomembranes

The effects of the glycoalkaloids alpha-solanine, alpha-chaconine and alpha-tomatine on different cell types were studied in order to investigate the membrane action of these compounds. Hemolysis of erythrocytes was compared to 6-carboxyfluorescein leakage from both ghosts and erythrocyte lipid vesicles, whereas leakage of enzymes from mitochondria and the apical and baso-lateral side of Caco-2 cells was determined. Furthermore, the effects of glycoalkaloids on the gap-junctional communication between Caco-2 cells was studied. From these experiments, it was found that glycoalkaloids specifically induced membrane disruptive effects of cholesterol containing membranes as was previously reported in model membrane studies. In addition, alpha-chaconine was found to selectively decrease gap-junctional intercellular communication. Furthermore, the glycoalkaloids were more potent in permeabilizing the outer membrane of mitochondria compared to digitonin at the low concentrations used.

The use of initiated cells as a test system for the detection of inhibitors of gap junctional intercellular communication

The effects of five non-mutagenic carcinogens--Aroclor 1260, benzoyl peroxide (BP), phenobarbital (PB), 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and 1,1'-(2,2,2-trichloroethylidene)bis[4-chlorobenzene] (DDT)--on gap junctional intercellular communication (GJIC) were tested in a cell line consisting of initiated cells (3PC). Four agents suspected of tumor promotion activity--o-anisidine, clofibrate, L-ethionone and d-limonene--were also tested for their effects on GJIC. Finally sodium fluoride (NaF), whose carcinogenic property is still unclear, was tested for its effects on GJIC in the 3PC cell line. Four of the five selected tumor promoters (Aroclor 1260, BP, DDT and TPA) decreased GJIC between these initiated epidermal cells. The four non-mutagenic carcinogens with tumor-promoting activity in vivo (o-anisidine, clofibrate, L-ethionine and d-limonene) all inhibited GJIC, whereas NaF had no effect. Seven compounds (o-anisidine, Aroclor 1260, BP, DDT, L-ethionine, d-limonene and TPA) had a dose-dependent as well as time-dependent inhibitory effect on GJIC. Under the experimental conditions used, clofibrate showed only a dose-related inhibition of GJIC. PB showed no inhibitory effect on GJIC in the 3PC cell line. In order to determine the role of biotransformation in the tumor-promoting activity of PB, its effect on GJIC was also examined in the presence of an Aroclor 1254-induced rat liver homogenate (S9 mix) and in the hepatoma cell line HepG2. In the presence of rat liver homogenate PB decreased GJIC in the 3PC cell line, whereas in the HepG2 cells PB showed a time- and dose-dependent inhibitory effect. To study the potential differences in susceptibility of cells representing different stages in the process of tumor formation, the effect of the selected tumor promoters on GJIC was also investigated in primary mouse keratinocytes and in a mouse skin carcinoma-derived cell line (CA3/7). Primary keratinocytes were sometimes more (BP and clofibrate) and sometimes less sensitive (ethionine and limonene) for inhibitory effects on GJIC compared to the effects in the cell line 3PC. Except for TPA and anisidin, GJIC between the CA3/7 cells was less affected by the selected agents compared to the 3PC cell line. These results show that, during the process of tumor formation the susceptibility of cells to inhibition of GJIC by tumor promoters is variable. Overall the CA3/7 cells are less sensitive compared to 3PC cells. The susceptibility of primary keratinocytes is variable compared to 3PC cells, depending on the agent used. These results also show that GJIC is a valid parameter for testing the tumor-promoting activity of compounds. Finally, this study demonstrates that mouse keratinocyte cell lines could serve as an in vitro model for the detection of non-mutagenic carcinogens with diverse target organs in vivo. For this use the cell line consisting of initiated cells (3PC) is more sensitive than the carcinoma-derived cell line CA3/7.

Molecular dosimetry of aflatoxin exposure: contribution to understanding the multifactorial etiopathogenesis of primary hepatocellular carcinoma with particular reference to hepatitis B virus

Aflatoxin exposure and hepatitis B virus infection have been implicated as major risk factors for primary hepatocellular carcinoma (PHC) in high-incidence regions of the world. Investigations using the assay of aflatoxin bound to peripheral blood albumin have shown that exposure can occur throughout the life span of the individual, including during the perinatal period, in high-incidence areas such as The Gambia, Senegal, Kenya, and The People's Republic of China. The possibility of measuring aflatoxin exposure at the individual level permits an investigation of the putative mechanisms of interaction of this carcinogen with HBV in the etiopathogenesis of PHC. Animal models, e.g., Pekin duck and HBV-transgenic mice, have also been used to study these questions, and the available data are reviewed.

Aflatoxin-albumin adducts in human sera from different regions of the world

An immunoassay now permits the determination of human exposure to aflatoxin at an individual level and consequently allows a better assessment of the role of aflatoxin, and its interaction with hepatitis B virus infection, in the aetiology of liver cancer. Measurements of aflatoxin bound to serum albumin in children and adults from various African countries show that between 12 and 100% contain aflatoxin-albumin adducts, with levels up to 350 pg AFB1-lysine equivalent/mg albumin. In Thailand, lower levels and prevalence of this adduct were observed, while no positive sera were detected from France or Poland. Data are presented showing that exposure to this carcinogen can occur throughout life and the relevance of these observations to the understanding of the multifactorial aetiology of liver cancer in these countries is discussed.