Increased Occurrence of Valproic Acid-Induced Hyperammonemia in Carriers of T1405N Polymorphism in Carbamoyl Phosphate Synthetase 1 Gene

The role of candidate pharmacogenetic variants in determining valproic acid efficacy, toxicity and concentrations in patients with epilepsy

Background

Antiseizure medications (ASM) exhibit considerable interindividual variability in terms of efficacy and adverse events. Genetic variation is thought to contribute to these differences in clinical outcomes. Specifically, the response to valproic acid (VPA), a widely used ASM, is influenced by multiple pharmacogenetic factors. However, and in contrast to other ASMs such as phenytoin and carbamazepine, there is a paucity of data on the association between VPA and various gene variants. The aim of this study was hence to evaluate the influence of candidate pharmacogenetic variants on VPA efficacy, toxicity and serum concentrations in a homogeneous cohort of patients newly diagnosed with genetic generalized epilepsies (GGE).

Methods

In this prospective cohort study, demographic, clinical and treatment outcomes of GGE patients were retrieved from their medical records. Whole exome sequencing was performed in collaboration with Epi25. Gene variants associated with VPA efficacy, metabolism and toxicities were retrieved from PharmGKB. An analysis was then conducted to explore potential associations between these gene variants and VPA clinical outcomes.

Results

Of the 166 patients included, 60 (36.1%) experienced treatment failure while 106 (63.9%) achieved treatment success. After adjusting for VPA maintenance dose, carriers of the rs3892097 (CYP2D6) variant were 2.5 times more likely to experience treatment failure compared to wildtype (p = 0.026). The rs1057910 variant (CYP2C9*3) was associated with increased serum VPA concentrations (p = 0.034). Moreover, the rs1137101 variant (LEPR gene, a metabolism regulator) was significantly associated with a higher risk of weight gain (regression coefficient of 3.430 [0.674; 6.186], p = 0.015) and a higher frequency of hair loss (OR = 3.394 [1.157; 9.956], p = 0.026), while the rs4480 variant (SOD2 gene, encoding for a mitochondrial scavenging enzyme) was correlated with a lower frequency of hair loss (OR = 0.276 [0.089; 0.858], p = 0.026).

Conclusion

These findings highlight the role of genetic factors in VPA treatment and underscore the potential for developing therapeutic strategies to enhance patient outcomes and minimize adverse effects.

Personalized antiseizure medication therapy in critically ill adult patients

Precision medicine has the potential to have a significant impact on both drug development and patient care. It is crucial to not only provide prompt effective antiseizure treatment for critically ill patients after seizures start but also have a proactive mindset and concentrate on epileptogenesis and the underlying cause of the seizures or seizure disorders. Critical illness presents different treatment issues compared with the ambulatory population, which makes it challenging to choose the best antiseizure medications and to administer them at the right time and at the right dose. Since there is a paucity of information available on antiseizure medication dosing in critically ill patients, therapeutic drug monitoring is a useful tool for defining each patient's personal therapeutic range and assisting clinicians in decision-making. Use of pharmacogenomic information relating to pharmacokinetics, hepatic metabolism, and seizure etiology may improve safety and efficacy by individualizing therapy. Studies evaluating the clinical implementation of pharmacogenomic information at the point-of-care and identification of biomarkers are also needed. These studies may make it possible to avoid adverse drug reactions, maximize drug efficacy, reduce drug-drug interactions, and optimize medications for each individual patient. This review will discuss the available literature and provide future insights on precision medicine use with antiseizure therapy in critically ill adult patients.

A Case of Carbamazepine-Induced Aggravation of Self-Limited Epilepsy with Centrotemporal Spikes Epilepsy and Valproate-Induced Hyperammonemic Encephalopathy in a Child with Heterozygous Gene Variant of Carbomoyl Phosphatase Synthetase Deficiency

Antiepileptics drugs are the mainstay of the management of epilepsy in children. Sodium valproate (VPA) and carbamazepine (CBZ) are widely used medications in childhood epilepsy. Hyperammonemia has been described as a known side effect of valproate therapy. It is known that VPA-associated HA is common among patients who hold genetic mutations of the carbomoyl phosphatase synthase 1 gene (CPS1). Aggravation of self-limited epilepsy with centrotemporal spikes (SLECTS) is a rare side effect of CBZ. Here, we present a child who had CBZ-induced aggravation of rolandic epilepsy and VPA-induced HA encephalopathy in the background of an unrecognised heterozygous gene variant of CPS1. An 8-year-old boy with SLECTS presented with a history of abnormal behaviours and drowsiness. He was apparently well until six years when he developed seizures in favour of rolandic epilepsy. His electroencephalogram (EEG) showed bilateral predominantly on the right-sided central-temporal spikes and waves. The diagnosis of SLECTS was made, and he was commenced on CBZ. Though he showed some improvement at the beginning, his seizure frequency increased when the dose of CBZ was increased. His repeat EEG showed electrical status in slow-wave sleep, and CBZ was stopped. Subsequently, he was started on VPA, and with that, he developed features of encephalopathy. He had elevated serum ammonia with normal liver functions. VPA was stopped with the suspicion of VPA-induced hyperammonemia. Tandem mass spectrometry did not show significant abnormality in the amino acid profile. Specific genetic analysis revealed a c.2756 C > T.p (Ser919Leu) heterozygote genetic mutation of the CSP 1 gene. This is a classic example where side effects of treatment determine the choice of antiepileptics drugs (AEDs) in childhood epilepsy. It is essential to keep in mind that SLECTS can be aggravated with certain AEDs, and VPA-induced HA in the absence of live failure could be due to underlying inherited metabolic disorders.

Myotoxicity Induced by Antiepileptic Drugs: Could be a Rare but Serious Adverse Event?

Antiepileptic drugs (AEDs) are used in various pathologies such as including epilepsy, migraine, neuropathic pain, etc. They can improve symptoms but cause adverse events (ADRs). Case reports have reported that one rare but serious AED-induced adverse reaction that has appeared in case reports is myotoxicity from rhabdomyolysis. Rhabdomyolysis can be induced by a therapeutically dosed occur with therapeutic doses of antiepileptic drugs and is in most cases reversible, although rarely it can cause serious complications. Clinical manifestations of rhabdomyolysis range from a single isolated asymptomatic rise in serum CK levels to severe electrolyte imbalances, cardiac arrhythmia, acute and disseminated renal failure, intravascular coagulation, and other symptoms. Many clinical cases reported that both conventional older and newer AEDs, as well as propofol, can cause rhabdomyolysis, even if there are no conclusive data. It has recently been shown that genetic factors certainly contribute to adverse reactions of antiepileptic drugs. A study of genetic polymorphism in patients with AED-induced rhabdomyolysis may be useful to explain the rarity of this adverse event and to improve the treatment of these AED patients, in terms of AED type and dose adjustment.

A catalog of genetic loci associated with kidney function from analyses of a million individuals

Chronic kidney disease (CKD) is responsible for a public health burden with multi-systemic complications. Through trans-ancestry meta-analysis of genome-wide association studies of estimated glomerular filtration rate (eGFR) and independent replication (n = 1,046,070), we identified 264 associated loci (166 new). Of these, 147 were likely to be relevant for kidney function on the basis of associations with the alternative kidney function marker blood urea nitrogen (n = 416,178). Pathway and enrichment analyses, including mouse models with renal phenotypes, support the kidney as the main target organ. A genetic risk score for lower eGFR was associated with clinically diagnosed CKD in 452,264 independent individuals. Colocalization analyses of associations with eGFR among 783,978 European-ancestry individuals and gene expression across 46 human tissues, including tubulo-interstitial and glomerular kidney compartments, identified 17 genes differentially expressed in kidney. Fine-mapping highlighted missense driver variants in 11 genes and kidney-specific regulatory variants. These results provide a comprehensive priority list of molecular targets for translational research.

CPS1 T1405N polymorphism, HDL cholesterol, homocysteine and renal function are risk factors of VPA induced hyperammonemia among epilepsy patients

PURPOSE

Valproic acid (VPA) is frequently used in the treatment of epilepsy. The adverse effects of VPA include hyperammonemia (HA) which is characterized by abnormally elevated blood ammonia level. Carbamoyl-Phosphate Synthase 1 (CPS1) is an enzyme catalyzing the initial step of removing ammonia from blood. Studies have demonstrated that the CPS1 polymorphism rs1047891-A allele carriers were susceptible to VPA-induced HA. However, the evidences remained controversial. In this study, we sought to validate the association between rs1047891 and VPA-induced HA by combining the association results from previous studies together.

METHODS

We first conducted a systematic meta-analysis to determine whether rs1047891 was statistically significant. Then, we further evaluated the pleiotropic effects of rs1047891 using published genome-wide association studies (GWAS) and UKBB results. A conditional analysis was conducted to investigate whether the association between rs1047891 and VPA-induced HA was mediated by cardiovascular or renal disease risk factors or vice versa.

RESULTS

The allelic, dominant and recessive ORs of rs1047891-A were all significant in our fixed-effect meta-analysis. In GWAS catalog and UKBB data, rs1047891 was associated with basal metabolic rate, adiposity and hematology traits, cardiovascular and renal disease risk factors. We further proved that plasma HDL cholesterol and homocysteine level, in addition to eGFR by serum creatinine, were associated with VPA-induced HA risk independently from rs1047891 polymorphism.

CONCLUSION

In conclusion, the SNP rs1047891 was associated with VPA-induce HA among epilepsy patients. Meanwhile, plasma HDL cholesterol and homocysteine level had independent effects from it.

Risk Factors for Valproic Acid-induced Hyperammonaemia in Chinese Paediatric Patients with Epilepsy

This study was aimed at identifying genetic and non-genetic risk factors for valproic acid (VPA)-induced hyperammonaemia in Chinese paediatric patients with epilepsy. A total of 210 epileptic patients, treated with VPA as monotherapy, were enrolled and classified into hyperammonaemia and control groups according to their blood ammonia level (cut-off value 50 μmol/L). Serum concentrations of VPA and its major metabolites were simultaneously determined by ultrahigh-performance liquid chromatography-tandem mass spectrometry. Six single nucleotide polymorphisms in the candidate genes, CYP2C9, CYP2A6, CYP2B6 and CPS1, were analysed by a matrix-assisted laser desorption ionization-time of flight mass spectrometry method or nested PCR. Significant differences in age, aspartate transaminase level and the incidence of liver injury were observed between patients of hyperammonaemia and control groups. Genotype distributions of CYP2C9*3, CYP2A6*4 and CPS1 4217C>A allelic variants were also significantly different between the two groups. According to multiple regression analysis, a significant negative correlation was detected between age and the blood ammonia level, while liver injury, the concentration-dose ratio (CDR) of VPA and 2-propyl-4-pentenoic acid (4-ene VPA), and the presence of CYP2A6*4 or CPS1 4217C>A showed positive correlations with the blood ammonia level. In addition, the risk factors for hyperammonaemia identified by logistic regression analysis were as follows: a younger age (odds ratio [OR] = 0.85; 95% confidence interval [CI] = 0.76-0.96; p = 0.007), occurrence of liver injury (OR = 4.60; 95% CI = 1.27-16.74; p = 0.021), higher CDR of 4-ene VPA (OR = 1.08; 95% CI = 1.03-1.14; p = 0.001), and carrying mutant alleles of CYP2C9*3 (OR = 3.42; 95% CI = 1.15-10.19; p = 0.028), CYP2A6*4 (OR = 3.23; 95% CI = 1.40-7.48; p = 0.006) and CPS1 4217C>A (OR = 3.25; 95% CI = 1.52-6.94; p = 0.002). Our findings indicated that multiple genetic and non-genetic risk factors that were identified can be used to predict the development of VPA-induced hyperammonaemia in Chinese paediatric patients with epilepsy.

The pharmacogenomics of valproic acid

Valproic acid is an anticonvulsant and mood-stabilizing drug used primarily in the treatment of epilepsy and bipolar disorder. Adverse effects of valproic acid are rare, but hepatotoxicity is severe in particular in those younger than 2 years old and polytherapy. During valproic acid treatment, it is difficult for prescribers to predict its individual response. Recent advances in the field of pharmacogenomics have indicated variants of candidate genes that affect valproic acid efficacy and safety. In this review, a large number of candidate genes that influence valproic acid pharmacokinetics and pharmacodynamics are discussed, including metabolic enzymes, drug transporters, neurotransmitters and drug targets. Furthermore, pharmacogenomics is an important tool not only in further understanding of interindividual variability but also to assess the therapeutic potential of such variability in drug individualization and therapeutic optimization.

Pharmacogenomics in epilepsy

•

Genetic variation can influence response to antiepileptic drug (AED) treatment through various effector processes.

•

Metabolism of many AEDs is mediated by the cytochrome P450 (CYP) family; some of the CYPs have allelic variants that may affect serum AED concentrations.

•

‘Precision medicine’ focuses on the identification of an underlying genetic aetiology allowing personalised therapeutic choices.

•

Certain human leukocyte antigen, HLA, alleles are associated with an increased risk of idiosyncratic adverse drug reactions.

•

New results are emerging from large-scale multinational efforts, likely imminently to add knowledge of value from a pharmacogenetic perspective.

There is high variability in the response to antiepileptic treatment across people with epilepsy. Genetic factors significantly contribute to such variability. Recent advances in the genetics and neurobiology of the epilepsies are establishing the basis for a new era in the treatment of epilepsy, focused on each individual and their specific epilepsy. Variation in response to antiepileptic drug treatment may arise from genetic variation in a range of gene categories, including genes affecting drug pharmacokinetics, and drug pharmacodynamics, but also genes held to actually cause the epilepsy itself.

From a purely pharmacogenetic perspective, there are few robust genetic findings with established evidence in epilepsy. Many findings are still controversial with anecdotal or less secure evidence and need further validation, e.g. variation in genes for transporter systems and antiepileptic drug targets. The increasing use of genetic sequencing and the results of large-scale collaborative projects may soon expand the established evidence.

Precision medicine treatments represent a growing area of interest, focussing on reversing or circumventing the pathophysiological effects of specific gene mutations. This could lead to a dramatic improvement of the effectiveness and safety of epilepsy treatments, by targeting the biological mechanisms responsible for epilepsy in each specific individual.

Whilst much has been written about epilepsy pharmacogenetics, there does now seem to be building momentum that promises to deliver results of use in clinic.