Graeme J. Sills

HLA-A*3101 and Carbamazepine-Induced Hypersensitivity Reactions in Europeans

BACKGROUND Carbamazepine causes various forms of hypersensitivity reactions, ranging from maculopapular exanthema to severe blistering reactions. The HLA-B*1502 allele has been shown to be strongly correlated with carbamazepine-induced Stevens-Johnson syndrome and toxic epidermal necrolysis (SJS-TEN) in the Han Chinese and other Asian populations but not in European populations. METHODS We performed a genomewide association study of samples obtained from 22 subjects with carbamazepine-induced hypersensitivity syndrome, 43 subjects with carbamazepine-induced maculopapular exanthema, and 3987 control subjects, all of European descent. We tested for an association between disease and HLA alleles through proxy single-nucleotide polymorphisms and imputation, confirming associations by high-resolution sequence-based HLA typing. We replicated the associations in samples from 145 subjects with carbamazepine-induced hypersensitivity reactions. RESULTS The HLA-A*3101 allele, which has a prevalence of 2 to 5% in Northern European populations, was significantly associated with the hypersensitivity syndrome (P=3.5×10(-8)). An independent genomewide association study of samples from subjects with maculopapular exanthema also showed an association with the HLA-A*3101 allele (P=1.1×10(-6)). Follow-up genotyping confirmed the variant as a risk factor for the hypersensitivity syndrome (odds ratio, 12.41; 95% confidence interval [CI], 1.27 to 121.03), maculopapular exanthema (odds ratio, 8.33; 95% CI, 3.59 to 19.36), and SJS-TEN (odds ratio, 25.93; 95% CI, 4.93 to 116.18). CONCLUSIONS The presence of the HLA-A*3101 allele was associated with carbamazepine-induced hypersensitivity reactions among subjects of Northern European ancestry. The presence of the allele increased the risk from 5.0% to 26.0%, whereas its absence reduced the risk from 5.0% to 3.8%. (Funded by the U.K. Department of Health and others.).

Predictors of pharmacoresistant epilepsy

Outcome data were analysed from 780 patients newly diagnosed with epilepsy and followed up at a single centre over a 20-year period to investigate which clinical factors predicted pharmacoresistance. Patients were divided at the time of analysis into those whose seizures had been controlled for at least the last 12 months of follow up (n=462) and those whose epilepsy remained refractory (n=318). Numbers of pre-treatment seizures were greater in uncontrolled patients. Those reporting more than 10 seizures prior to initiation of therapy were more than twice as likely to develop refractory epilepsy. Univariate and multivariate logistic regression analyses demonstrated that pharmacoresistance was also associated with family history of epilepsy, previous febrile seizures, traumatic brain injury as the cause of the epilepsy, intermittent recreational drug use, and prior or current psychiatric comorbidity, particularly depression. Factors not predicting poorer outcome included gender, neurological deficit and mental retardation. The most interesting new finding was the correlation between psychiatric comorbidity and lack of response to antiepileptic drug therapy. The deleterious neurobiological processes that underpin depression, anxiety and psychosis may interact with those producing seizures to increase the extent of brain dysfunction and thereby the likelihood of developing pharmacoresistant epilepsy.

The mechanisms of action of commonly used antiepileptic drugs.

In the past decade, nine new drugs have been licensed for the treatment of epilepsy. With limited clinical experience of these agents, the mechanisms of action of antiepileptic drugs may be an important criterion in the selection of the most suitable treatment regimens for individual patients. At the cellular level, three basic mechanisms are recognised: modulation of voltage-dependent ion channels, enhancement of inhibitory neurotransmission, and attenuation of excitatory transmission. In this review, we will attempt to introduce the concepts of ion channel and neurotransmitter modulation and, thereafter, group currently used antiepileptic drugs according to their principal mechanisms of action.

Lack of Association between the C3435T Polymorphism in the Human Multidrug Resistance (MDR1) Gene and Response to Antiepileptic Drug Treatment

Summary:  Purpose: P‐glycoprotein (P‐gp) has been implicated in the causation of refractory epilepsy. The expression and efflux efficiency of P‐gp is influenced by a polymorphism (C3435T) in the encoding gene (MDR1). Recent evidence suggests that the homozygous C‐variant, which is associated with higher expression and increased activity of P‐gp, is more common in patients with pharmacoresistant epilepsy. We have investigated the prevalence of this polymorphism in a series of patients attending a specialist epilepsy clinic.

Bone density and antiepileptic drugs: a case-controlled study

This case-controlled study explored the relationship between bone mineral density (BMD) and long-term treatment with antiepileptic drugs (AEDs) in older adults with epilepsy. Seventy-eight patients (47 post-menopausal females, 31 males, aged 47-76 years) with epilepsy participated in the study. Each had only ever received treatment with either enzyme-inducing (n = 52) or non-inducing (n = 26) AEDs. Individuals were matched for age, sex, height and weight with a drug-naive control. All patients underwent bone densitometry at the lumbar spine and femoral neck and had blood sampling and urine collected for a range of bone markers. Male patients had lower BMD than controls at the lumbar spine (P < 0.01) and neck of the femur (P < 0.005). Female patients had significantly reduced bone density at the femoral neck (P < 0.05) only. AED usage was independently associated with an overall reduction in bone density at femoral sites and contributed to just over 5% of the variance at the femoral neck. Duration of treatment and type of AED were not independent factors for reduction in BMD. This case-controlled study supports the hypothesis that long-term AED therapy is an independent risk factor for reduced BMD in epileptic patients. Adults receiving treatment for epilepsy are at higher risk of osteoporosis and should be offered bone densitometry.

Sudden unexpected death in epilepsy: A search for risk factors

Sudden unexpected death in epilepsy (SUDEP) is the commonest cause of seizure-related mortality in people with refractory epilepsy. Of the 6140 patients registered with the Epilepsy Unit at the Western Infirmary in Glasgow between 1982 and 2005, 529 had died, 62 (11.7%) of whom succumbed to SUDEP. All but 2 deaths occurred at home; 3 were witnessed. Two living controls were matched with each SUDEP case for year of birth, gender, and syndromic classification. Mean duration of epilepsy was significantly longer in cases compared with controls (P=0.001). More people succumbing to SUDEP had had a seizure within the previous year (P=0.007). There were no significant associations between SUDEP and a history of generalized tonic-clonic seizures, drug polytherapy, and current use of carbamazepine. There is an urgent need for a large-scale, prospective, international, community-based study of SUDEP to explore more closely the risk factors to plan preventive strategies.

Prevalence of neurologic autoantibodies in cohorts of patients with new and established epilepsy

Autoantibodies to specific neurologic proteins are associated with subacute onset encephalopathies, which often present with seizures that are poorly controlled by conventional antiepileptic drugs (AEDs). Previous cross‐sectional studies have found specific neurologic antibodies in a small proportion of people with established epilepsy, but these investigations have seldom included patients with recent diagnosis.

P-glycoprotein-mediated efflux of antiepileptic drugs: preliminary studies in mdr1a knockout mice.

Evidence suggests that the efflux transporter P-glycoprotein (P-gp) may play a facilitatory role in refractory epilepsy by limiting the brain access of antiepileptic drugs (AEDs). We have conducted a preliminary pharmacokinetic study of seven commonly used AEDs in mdr1a knockout mice, devoid of P-gp at the blood-brain barrier. A parallel group of matched wild-type mice served as controls. AEDs were administered by subcutaneous injection and serum and brain drug concentrations determined at 30, 60, and 240min post-dosing. The brain-serum concentration ratio for topiramate was higher in mdr1a(-/-) mice than in wild-type controls at all time points investigated. No consistent effects were observed with any other AED investigated. These findings suggest that topiramate may be a substrate for P-gp-mediated transport. Further studies employing a range of model systems are required to substantiate this observation and to address the potential role of drug transporters in refractory epilepsy.

Topiramate in Refractory Epilepsy: A Prospective Observational Study

Summary: Purpose: This prospective observational study explored the efficacy and tolerability of topiramate (TPM) in patients with refractory epilepsy attending a single outpatient clinic.

Antiepileptic drug therapy: Does mechanism of action matter?

This article represents a synthesis of presentations made by the authors during a scientific meeting held in London on 7 June 2010 and organized by GlaxoSmithKline. Each speaker produced a short précis of his lecture to answer a specific question, resulting in an overview of what we know about the relevance of the mechanisms of action of antiepileptic drugs in determining appropriate combination therapies for the treatment of drug-resistant epilepsy.