Pharmacogenomics in the treatment of narcolepsy

Pharmacological options for narcolepsy: are they the way forward?

INTRODUCTION

Narcolepsy is an under-recognized, rare neurologic disorder of hypersomnolence that is associated with increased mortality and medical and psychiatric co-morbidities. Narcolepsy exerts a substantial economic burden on patients and society. There is currently no cure, and life-long symptomatic therapy is needed. Available drugs do not modify the disease course.

AREAS COVERED

This manuscript provides an overview of narcolepsy symptoms, diagnosis, pathophysiology, current pharmacotherapies, and emerging treatments. Gaps and unresolved issues in diagnosis and management of narcolepsy are discussed to answer whether pharmacological options are the way forward.

EXPERT OPINION

Diagnostic criteria for narcolepsy (ICSD-3) need revision and greater clarity. Improved recognition of cataplexy and other symptoms through educational outreach, new biomarkers, improved test scoring through artificial intelligence algorithms, and use of machine learning may facilitate earlier diagnosis and treatment. Pharmacological options need improved symptomatic therapy in addition to targeted therapies that address the loss of hypocretin signaling. Optimal narcolepsy care also needs a better understanding of the pathophysiology, recognition of the different phenotypes in narcolepsy, identification of at-risk individuals and early recognition of symptoms, better diagnostic tools, and a database for research and disease monitoring of treatment, side-effects, and comorbidities.

Pharmacogenomic Biomarkers

Why does the usual dose of medication work for a person while another individual cannot give the expected response to the same drug? On the other hand, how come half of the usual dose of an analgesic relieves an individual’s pain immediately, as another man continue to suffer even after taking double dose? Although a treatment method has been successfully used in majority of the population for many years, why does the same therapy cause serious side effects in another region of the world? Most presently approved therapies are not effective in all patients. For example, 20-40% of patients with depression respond poorly or not at all to antidepressant drug therapy. Many patients are resistant to the effects of antiasthmatics and antiulcer drugs or drug treatment of hyperlipidemia and many other diseases. The reason for all those is basically interindividual differences in genomic structures of people, which are explained in this chapter in terms of the systems and the most frequently used drugs in clinical treatment.

Association of narcolepsy-cataplexy with HLA-DRB1 and DQB1 in Mexican patients: a relationship between HLA and gender is suggested

Background

Narcolepsy-cataplexy is characterized by excessive daytime sleepiness with recurrent episodes of irresistible sleep, cataplexy, hallucinations and sleep paralysis. Its aetiology is unknown, but it is positively associated with the human leukocyte antigens (HLA) in all studied populations. The purpose of the present study was to investigate the association of HLA class II DRB1/DQB1 alleles with narcolepsy-cataplexy in Mexican Mestizo patients.

Methods

This is a case-control study of consecutive patients and ethnically matched controls. We included 32 patients diagnosed with typical narcolepsy-cataplexy, of the National Institute of Neurology, of the Institute of Psychiatry and at the Center of Narcolepsy at Stanford University. As healthy controls, 203 Mexican Mestizos were included. DRB1 alleles were identified using sequence based typing. A PCR-SSOP reverse dot blot was used for DQB1 typing. Allele frequency was calculated by direct counting and the significance of the differences was assessed using the Yates Chi square. Odds ratio and confidence intervals were evaluated.

Results

HLA-DRB1*1501 (OR = 8.2; pc < 0.0001) and DQB1*0602 (OR = 8.4; pc < 0.0001) were found positively associated with narcolepsy. When deleting DQB1*0602+ patients from the analysis, DQB1*0301 was also found increased (OR = 2.7; p = 0.035; pc = NS). DQB1*0602/DQB1*0301 genotype was present in 15.6% of the cases (OR = 11.5; p = 0.00035), conferring a high risk. DRB1*0407 (OR = 0.2; p = 0.016 pc = NS) and DQB1*0302(OR = 0.4; p = 0.017, pc = NS) were found decreased in the patients. The gender stratification analysis showed a higher risk in females carrying DRB1*1501 (OR = 15.8, pc < 0.0001) and DQB1*0602 (OR = 19.8, pc < 0.0001) than in males (OR = 5.0 for both alleles; p = 0.012, pc = NS for DRB1 & p = 0.0012, pc = 0.017 for DQB1). The susceptibility alleles found in Mexicans with narcolepsy are also present in Japanese and Caucasians; DRB1*04 linked protection has also been shown in Koreans. A stronger HLA association is suggested in females, in accordance with the sexual dimorphism claimed previously.

Conclusion

This knowledge may contribute to a better understanding of the disease pathogenesis in different populations. The evaluation of the risk to develop narcolepsy-cataplexy in carriers of the described alleles/genotypes may also be possible. A larger sample should be analysed in Mexican and in other Hispanic patients to confirm these results.

Pediatric sleep pharmacology

This article reviews the most common pharmacologic options in the treatment of sleep disorders in children. Despite the high prevalence of sleep disorders in children, there is a paucity of education and information available on the pharmacologic management of sleep disorders in children. The principles of sleep physiology and pathophysiology that help provide more rational pharmacologic management are discussed. Medications are typically not Food and Drug Administration (FDA) approved for the pediatric age range or for the specific sleep disorder. Medications have a role for insomnia, narcolepsy, parasomnias, and sleep-related movement disorders. The available choices of hypnotics are reviewed. Medications to increase alertness of narcoleptics and decrease cataplexy are discussed. The use of dopaminergic agents for Restless Legs Syndrome is reviewed. The potential use of medication in sleep apnea is also reviewed. Pharmacologic guidelines need to be developed specifically for sleep disorders in children. Ideally, these guidelines should be FDA approved for the specific sleep disorder and for the pediatric age range. The development of easy to swallow, chewable or liquid forms of these medications are needed. Training programs should play the lead role in enhancing pediatricians' knowledge of the pharmacologic treatment of sleep disorders in children.

The integration of personalized and systems medicine: bioinformatics support for pharmacogenomics and drug discovery

Pharmacogenomics may have a deep impact on every drug treatment protocol to bring the right drug to the right patient. While pharmacogenomics can help achieve individualized medicine, the study of systems biology can help us understand the key issues in pharmacogenomics at different levels. These key issues include the associations between structure and function, the correlations between genotype and phenotype, and the interactions among gene, drug, and environment. Utilizing bioinformatics in pharmacogenomics that is conducted in a systemic way can help integrate information from different levels. At the molecular level, the detailed features of a gene and the relationship between genetic structure and function need to be explored. These detailed features include sequence analytic information such as sequence retrieval and structural modeling, sequence variation information, and sequence patterns that can correlate sequence structure to functional motifs. At the cellular level, the interactions and networks among those molecules should be examined. Higher degrees of understanding at the tissue and organism levels can help establish the correlations between genotype and phenotype. The application of bioinformatics methods in pharmacogenomics and systems biology should enable a more profound understanding of diseases at different levels and lead to both individualized and systems medicine. To facilitate up-to-date bio-informatics support, an integrated search engine and updated collections of tools are freely available at http://sysmed.pharmtao.com.

Pharmacogenetic tools for the development of target-oriented cognitive-enhancing drugs

The identification of the anatomical and physiological substrates involved in the regulation of the dorsolateral prefrontal cortex function in humans provided the basis for the understanding of mechanisms involved in cognitive and executive function under normal as well as pathological conditions. In this context, substantial evidence indicates that alterations in monaminergic function in the dorsolateral prefrontal cortex significantly contributes to the cognitive impairments present in schizophrenia, attention deficit disorders, and other neuropsychiatric conditions. The development of a number of compounds that selectively increase extracellular dopamine (DA) concentrations in the dorsolateral prefrontal cortex but not in subcortical areas by either blocking its metabolism or reuptake, or increasing its release, or that directly activate postsynaptic DA-1 receptor mechanisms provided powerful pharmacotherapeutic tools to mitigate the cognitive deficits brought about by the dopaminergic alterations of the prefrontal cortex. More recently, the findings that polymorphisms of the catecholamine-O-methyl-transferase gene may also modify the effect of these drugs on the prefrontal cortex points toward a more specific genotype-based neuropsychopharmacology for the treatment of cognitive deficits in schizophrenia as well as in a number of other neuropsychiatric conditions. The ability of these compounds to increase DA load selectively in the frontal cortex and not on subcortical systems allows a targeted intervention without the stimulant-like effects observed with older drugs used to treat those conditions.

Sex differences in mouse behavior following pyrilamine treatment: role of histamine 1 receptors in arousal

Arousal, the activation of brain and behavior, is a fundamental component of behavior. While sex differences in behavior are pervasive, it is unknown whether they could be due to an underlying dimorphism in arousal mechanisms. Because histamine (HA) acting through histamine 1 (H1) receptors is one essential component of arousal neural circuitry, the aim of the current experiment was to measure sex differences in behavioral arousal following treatment with the H1 receptor antagonist, pyrilamine (PYRL). Castrated male and ovariectomized female Swiss-Webster mice were treated subcutaneously with either 15 or 35 mg/kg of PYRL. The effect of drug treatment was determined in an array of behaviors: sensory responsiveness, running wheel activity, and fearfulness. Surprisingly, the lower dose of PYRL increased some aspects of arousal, sensory responsiveness, and anxiety-like behavior, while the higher dose of PYRL resulted in decreases in arousal across tests, indicating that antagonism of histamine receptors does not have a linear relationship with arousal. Females were more sensitive to the arousal-reducing effects of PYRL than males in sensory and running wheel tasks but not in tests of emotion. In conclusion, antagonism of H1 receptors can alter arousal in a sex-dependent manner, independent of circulating gonadal steroids, in mice.

Genes for normal sleep and sleep disorders

Sleep and wakefulness are complex behaviors that are influenced by many genetic and environmental factors, which are beginning to be discovered. The contribution of genetic components to sleep disorders is also increasingly recognized as important. Point mutations in the prion protein, period 2, and the prepro-hypocretin/orexin gene have been found as the cause of a few sleep disorders but the possibility that other gene defects may contribute to the pathophysiology of major sleep disorders is worth in-depth investigations. However, single gene disorders are rare and most common disorders are complex in terms of their genetic susceptibility, environmental effects, gene-gene, and gene-environment interactions. We review here the current progress in the genetics of normal and pathological sleep.

Women's sleep in health and disease

A huge amount of knowledge about sleep has accumulated during the last 5 decades following the discovery of rapid eye movement (REM) sleep. Nevertheless, there are numerous areas of considerable ignorance. One of these concerns the particularities of sleep in women. Most basic and clinical studies have been performed in male subjects, and only very recently research groups around the world have addressed women's sleep in health and disease. In this review, we summarize the present knowledge on the influence of oestrogens on the brain and on the distinctive changes of sleep across the menstrual cycle, during pregnancy and menopause. In addition, studies in female rodents are reviewed as well as the knowledge on female peculiarities regarding the interactions between sleep regulation and age-related changes in circadian rhythms. We also address specific aspects of sleep loss and sleep disorders in women. Finally, very recent studies on the sociology of sleep are summarized and future directions in the field are discussed.

Variants of the orexin2/hcrt2 receptor gene identified in patients with excessive daytime sleepiness and patients with Tourette's syndrome comorbidity

The orexin-2/hypocretin-2 (OX2R) receptor gene is mutated in canine narcolepsy and disruption of the prepro-orexin/hypocretin ligand gene results in both an animal model of narcolepsy and sporadic cases of the human disease. This evidence suggests that the structure of the OX2R gene, and its homologue, the OX1R gene, both members of the G protein-coupled receptor (GPCR) family, and the gene encoding the peptide ligands, the prepro-orexin/hypocretin gene, may be variables in the etiology of sleep disorders. We report a single stranded conformational polymorphism (SSCP) analysis of the coding regions of these genes in idiopathic sleep disorder patients diagnosed with excessive daytime sleepiness (EDS) (n = 28), narcolepsy (n = 28), Tourette's syndrome/chronic vocal or motor tic disorder (n = 70), and control subjects (n = 110). Two EDS patients showed a Pro11Thr change. One Tourette's syndrome patient was found to have a Pro10Ser alteration. The Pro10Ser and Pro11Thr variants were not found in non-disease populations. Analysis of the ability of the mutant receptors to mobilize calcium compared to the wild-type receptor in response to orexin agonists indicated that they resulted in decreased potency at high (etaM) concentrations of orexin ligands. Further work is warranted to study the variability of the orexin/hypocretin system in a variety of disorders characterized by EDS.

Pediatric sleep pharmacology: you want to give my kid sleeping pills?

There is a need for greater information about the pharmacologic management of sleep disorders in children. Pharmacologic guidelines must be developed specifically for sleep disorders in children. Ideally, these guidelines should be approved by the Food and Drug Administration for a specific sleep disorder or for the pediatric age range. This approval prevents physicians from being forced to prescribe medications as an "off label" indication. Development of easy-to-swallow, chewable, or liquid forms of these medications would be well received by parents everywhere. When these are not available, instructions for compounding these medications into a suspension by pharmacists are needed. Integration of behavioral and pharmacologic treatments may yield better patient outcomes. This approach requires pediatricians to have a comprehensive understanding of clinical sleep disorders in children. Training programs should play the lead role in enhancing pediatricians' knowledge of the pharmacologic treatment of sleep disorders in children.