Association study of the interleukin-1 beta (C-511T) genetic polymorphism with major depressive disorder, associated symptomatology, and antidepressant response

Evidence from biomarkers and surrogate endpoints

The use of physiological, anatomical, and other biological tests is commonplace in the practice of medicine. In neurology, objectively measured tests termed biomarkers (BMs) are playing an increasing role in diagnosis and management of disease, both in clinical practice and in experimental therapeutics. This article will discuss the various applications of BMs to the assessment of therapies for neurological diseases and will use examples from neurological diseases to elucidate the strengths and potential weaknesses of BMs. As the understanding of the pathophysiology of many neurological diseases has improved, new BMs have been developed, and efforts have been made to use these as proxies for clinical endpoints. A BM used in this manner is referred to as a surrogate endpoint (SE). There are many potential advantages and disadvantages of using SEs in the evaluation of new therapies, and these will be reviewed as well. Furthermore, the evidence required for the development of an SE and the nature of the evidence that can be derived from the use of BMs and SEs will be discussed.

Candidate genes for antidepressant response to selective serotonin reuptake inhibitors

Selective serotonin reuptake inhibitors (SSRIs) can safely and successfully treat major depression, although a substantial number of patients benefit only partially or not at all from treatment. Genetic polymorphisms may play a major role in determining the response to SSRI treatment. Nonetheless, it is likely that efficacy is determined by multiple genes, with individual genetic polymorphisms having a limited effect size. Initial studies have identified the promoter polymorphism in the gene coding for the serotonin reuptake transporter as moderating efficacy for several SSRIs. The goal of this review is to suggest additional plausible polymorphisms that may be involved in antidepressant efficacy. These include genes affecting intracellular transductional cascades; neuronal growth factors; stress-related hormones, such as corticotropin-releasing hormone and glucocorticoid receptors; ion channels and synaptic efficacy; and adaptations of monoaminergic pathways. Association analyses to examine these candidate genes may facilitate identification of patients for targeted alternative therapies. Determining which genes are involved may also assist in identifying future, novel treatments.

Pharmacogenetics in the treatment of depression: pharmacodynamic studies

The pharmacological treatment of mood disorders has reduced their morbidity and improved mental health for millions of individuals worldwide, favouring a considerable reduction of the direct and indirect costs caused by these common pathologies. Unfortunately, not all individuals benefit, and 30-40% of patients do not show a complete response to treatment. Efficient clinical predictors are not available, although genetic factors are thought to play a substantial (but complex) role in the antidepressant response. Pharmacogenetics, which investigates the influence of genetic features on the pharmacological response, has gained increasing attention and holds great promise for clinical psychiatry. Here, a brief overview is provided on the various pharmacogenetic studies published to date that analyse the commonest treatments for depression: antidepressants, sleep deprivation and lithium salts.

Proposed multigenic Composite Inheritance in major depression

Various rationale have been considered in the familial inheritance pattern of major depression ranging from simple one-gene Mendelian inheritance to pseudo-additive gene action. We instead predict broad genetic expressivity patterns in the progeny of parents where at least one parent has recurrent major depression. In keeping with this idea, we feel that recurrent major depression could involve an expression imbalance of "normal" genes either exclusively or along with allelic variation(s). The patterns of pathology are theoretically conceptualized as qualitative and quantitative, meaning that expressivity of the genetic pattern in these children may range from minimal to complete even among siblings. Thus, prediction of the particular genetic pattern expressed by a particular child might prove difficult. The complex inheritance pattern that we propose is referred to as Composite Inheritance. Composite Inheritance considers that both the up- and down-regulation of luxury genes and housekeeping genes are involved in this dichotomous qualitative inheritance pattern and also the wide quantitative expressivity. The luxury genes include such genes as those coding for the neurotransmitter transporters and receptors. The housekeeping genes found to date include those that code for proteins involved in gene transcription, secondary signaling systems, fatty acid metabolism and transport, and intracellular calcium homeostasis. Other luxury and housekeeping genes no doubt remain to be discovered. Our current research utilizes an empirical approach involving advanced genomics and specialized pattern recognition mathematics in families having at least one parent with recurrent major depression. The goal of our research is to develop a pattern recognition system of genetic expressivity in major depression to which prevention and early intervention may be tailored.

Analysis of IL-1alpha, IL-1beta, and IL-1RA [correction of IL-RA] polymorphisms in dysthymia

Investigators of independent studies reported alterations in cytokine serum levels in patients with different mood disorders. Several polymorphisms associated with neuropsychiatric disorders such as schizophrenia and Alzheimer's disease have been reported at the interleukin-1 (IL-1) panel. Here we report the results of three specific polymorphisms at the IL-1alpha, IL-1beta, and IL-1RA genes, which were analyzed in 128 Brazilian subjects: 59 dysthymic patients and 69 normal controls. We found a statistically significant difference (p = 0.002) in the frequency of haplotypes with alleles 2+ (IL-1RA), T+ (IL-1alpha), and C+ (IL-1beta) in patients as compared to controls. We also observed that haplotype IL-1RA1.2/IL-1alpha CT/IL-1beta CC, present in 6 dysthymic patients (10%) was absent in the normal control group (p = 0.012). These results suggest that these polymorphisms might confer a greater susceptibility to develop dysthymia in Brazilian patients. However, to validate these data it will be of great interest to repeat this study in larger samples and other ethnic groups.

Pharmacogenetics of antidepressants and antipsychotics: the contribution of allelic variations to the phenotype of drug response

Genetic factors contribute to the phenotype of drug response. We systematically analyzed all available pharmacogenetic data from Medline databases (1970-2003) on the impact that genetic polymorphisms have on positive and adverse reactions to antidepressants and antipsychotics. Additionally, dose adjustments that would compensate for genetically caused differences in blood concentrations were calculated. To study pharmacokinetic effects, data for 36 antidepressants were screened. We found that for 20 of those, data on polymorphic CYP2D6 or CYP2C19 were found and that in 14 drugs such genetic variation would require at least doubling of the dose in extensive metabolizers in comparison to poor metabolizers. Data for 38 antipsychotics were examined: for 13 of those CYP2D6 and CYP2C19 genotype was of relevance. To study the effects of genetic variability on pharmacodynamic pathways, we reviewed 80 clinical studies on polymorphisms in candidate genes, but those did not for the most part reveal significant associations between neurotransmitter receptor and transporter genotypes and therapy response or adverse drug reactions. In addition associations found in one study could not be replicated in other studies. For this reason, it is not yet possible to translate pharmacogenetic parameters fully into therapeutic recommendations. At present, antidepressant and antipsychotic drug responses can best be explained as the combinatorial outcome of complex systems that interact at multiple levels. In spite of these limitations, combinations of polymorphisms in pharmacokinetic and pharmacodynamic pathways of relevance might contribute to identify genotypes associated with best and worst responders and they may also identify susceptibility to adverse drug reactions.

The pharmacogenomics of selective serotonin reuptake inhibitors

The introduction of selective serotonin (5-HT) reuptake inhibitors (SSRIs) has significantly improved the pharmacological treatment of a range of psychiatric disorders. Nevertheless, despite the undoubted advantages of antidepressant treatment in terms of improved tolerability to therapy while maintaining a high level of efficacy, not all patients benefit from it; an appreciable proportion do not respond adequately, while others may show adverse reactions. The necessary change of the initial treatment choice often requires extended periods for the remission of symptomatology. Such difficulties could be avoided if it should be possible to determine more quickly the most suitable drug. Several factors have been thought to influence the outcome of antidepressant therapy. Among the factors influencing the interindividual variability in response to treatment with SSRI, differences in genetic features may play a significant role. Several genetic polymorphisms have been associated with therapeutic SSRI response, including genetic variants of the 5-HT transporter, 5-HT-2A-receptor, tryptophan hydroxylase, brain-derived neurotrophic factor, G-protein beta3 subunit, interleukin-1beta and angiotensin-converting enzyme, although with conflicting results; also cytochrome P450 drug-metabolising enzymes may bear a particular importance, although further corroboration of the findings is necessary, and further key participating genes remain to be identified. The hope is that the identification of these genetic components will eventually facilitate the development of a customised SSRI treatment.