The genetic interacting landscape of 63 candidate genes in Major Depressive Disorder: an explorative study

Background

Genetic contributions to major depressive disorder (MDD) are thought to result from multiple genes interacting with each other. Different procedures have been proposed to detect such interactions. Which approach is best for explaining the risk of developing disease is unclear.

This study sought to elucidate the genetic interaction landscape in candidate genes for MDD by conducting a SNP-SNP interaction analysis using an exhaustive search through 3,704 SNP-markers in 1,732 cases and 1,783 controls provided from the GAIN MDD study. We used three different methods to detect interactions, two logistic regressions models (multiplicative and additive) and one data mining and machine learning (MDR) approach.

Results

Although none of the interaction survived correction for multiple comparisons, the results provide important information for future genetic interaction studies in complex disorders. Among the 0.5% most significant observations, none had been reported previously for risk to MDD. Within this group of interactions, less than 0.03% would have been detectable based on main effect approach or an a priori algorithm. We evaluated correlations among the three different models and conclude that all three algorithms detected the same interactions to a low degree. Although the top interactions had a surprisingly large effect size for MDD (e.g. additive dominant model P_uncorrected = 9.10E-9 with attributable proportion (AP) value = 0.58 and multiplicative recessive model with P_uncorrected = 6.95E-5 with odds ratio (OR estimated from β3) value = 4.99) the area under the curve (AUC) estimates were low (< 0.54). Moreover, the population attributable fraction (PAF) estimates were also low (< 0.15).

Conclusions

We conclude that the top interactions on their own did not explain much of the genetic variance of MDD. The different statistical interaction methods we used in the present study did not identify the same pairs of interacting markers. Genetic interaction studies may uncover previously unsuspected effects that could provide novel insights into MDD risk, but much larger sample sizes are needed before this strategy can be powerfully applied.

Preliminary evidence that early reduction in p11 levels in natural killer cells and monocytes predicts the likelihood of antidepressant response to chronic citalopram

The prediction of treatment response in many neuropsychiatric disorders would be facilitated by easily accessible biomarkers. Using flow cytometry, we herein demonstrate correlations between early reductions of p11 levels in Natural Killer (NK) cells and monocytes and antidepressant response to citalopram in patients with major depressive disorder (MDD).

Mood stabilizer treatment increases serotonin type 1A receptor binding in bipolar depression

Abnormal serotonin type 1A (5-HT1A) receptor function and binding have been implicated in the pathophysiology of mood disorders. Preclinical studies have consistently shown that stress decreases the gene expression of 5-HT1A receptors in experimental animals, and that the associated increase in hormone secretion plays a crucial role in mediating this effect. Chronic administration of the mood stabilizers lithium and divalproex (valproate semisodium) reduces glucocorticoid signaling and function in the hippocampus. Lithium has further been shown to enhance 5-HT1A receptor function. To assess whether these effects translate to human subject with bipolar disorder (BD), positron emission tomography (PET) and [18F]trans-4-fluoro-N-(2-[4-(2-methoxyphenyl) piperazino]-ethyl)-N-(2-pyridyl) cyclohexanecarboxamide ([(18)F]FCWAY) were used to acquire PET images of 5-HT1A receptor binding in 10 subjects with BD, before and after treatment with lithium or divalproex. Mean 5-HT1A binding potential (BPP) significantly increased following mood stabilizer treatment, most prominently in the mesiotemporal cortex (hippocampus plus amygdala). When mood state was also controlled for, treatment was associated with increases in BPP in widespread cortical areas. These preliminary findings are consistent with the hypothesis that these mood stabilizers enhance 5-HT1A receptor expression in BD, which may underscore an important component of these agents' mechanism of action.

Frequency of mutations in the genes associated with hereditary sensory and autonomic neuropathy in a UK cohort

The hereditary sensory and autonomic neuropathies (HSAN, also known as the hereditary sensory neuropathies) are a clinically and genetically heterogeneous group of disorders, characterised by a progressive sensory neuropathy often complicated by ulcers and amputations, with variable motor and autonomic involvement. To date, mutations in twelve genes have been identified as causing HSAN. To study the frequency of mutations in these genes and the associated phenotypes, we screened 140 index patients in our inherited neuropathy cohort with a clinical diagnosis of HSAN for mutations in the coding regions of SPTLC1, RAB7, WNK1/HSN2, FAM134B, NTRK1 (TRKA) and NGFB. We identified 25 index patients with mutations in six genes associated with HSAN (SPTLC1, RAB7, WNK1/HSN2, FAM134B, NTRK1 and NGFB); 20 of which appear to be pathogenic giving an overall mutation frequency of 14.3%. Mutations in the known genes for HSAN are rare suggesting that further HSAN genes are yet to be identified. The p.Cys133Trp mutation in SPTLC1 is the most common cause of HSAN in the UK population and should be screened first in all patients with sporadic or autosomal dominant HSAN.

Routine detection and management of neurocognitive impairment in HIV-positive patients in a UK centre

We estimated the burden of HIV-associated neurocognitive disorders (HAND) in a UK clinic. From a random sample, and referrals to specialist services over one year (neurology, clinical psychology, hospital admissions), we determined whether patients were diagnosed with HIV-associated dementia (HAD) and whether they reported symptoms suggesting neurocognitive impairment (NCI). In the first sample, 2/150 (prevalence 1.3%; 95% confidence interval [CI] 0.2–4.7%) had documented HAD. Eleven patients (7.3%; CI 3.7–12.7%) reported recent symptoms suggesting NCI; most of these individuals were diagnosed with a psychiatric or substance-use disorder. Among specialist referrals with symptoms suggesting NCI, 11 were diagnosed with HAD from a clinic population of 3129 individuals (annual incidence 0.4%; CI 0.2–0.6%). No patients with mildly symptomatic or asymptomatic HAND were identified in either sample, suggesting that such patients remain undetected in current clinical practice. Evidence-based screening for HAND in HIV clinics may be needed.

Neuroprotective effects of low-dose lithium in individuals at ultra-high risk for psychosis. A longitudinal MRI/MRS study

OBJECTIVES

To investigate if low-dose lithium may counteract the microstructural and metabolic brain changes proposed to occur in individuals at ultra-high risk (UHR) for psychosis.

METHODS

Hippocampal T2 relaxation time (HT2RT) and proton magnetic resonance spectroscopy ((1)H-MRS) measurements were performed prior to initiation and following three months of treatment in 11 UHR patients receiving low-dose lithium and 10 UHR patients receiving treatment as usual (TAU). HT2RT and (1)H-MRS percentage change scores between scans were compared using repeated measures ANOVA and correlated with behavioural change scores.

RESULTS

Low-dose lithium significantly reduced HT2RT compared to TAU (p=0.018). No significant group by time effects was seen for any brain metabolites as measured with (1)H-MRS, although myo-inositol, creatine, choline-containing compounds and NAA increased in the group receiving low-dose lithium and decreased or remained unchanged in subjects receiving TAU.

CONCLUSIONS

This pilot study suggests that low-dose lithium may protect the microstructure of the hippocampus in UHR states as reflected by significantly decreasing HT2RT. Larger scale replication studies in UHR states using T2 relaxation time as a proxy for emerging brain pathology seem a feasible mean to test neuroprotective strategies such as low-dose lithium as potential treatments to delay or even prevent the progression to full-blown disorder.

Hand weakness in Charcot-Marie-Tooth disease 1X

There have been suggestions from previous studies that patients with Charcot-Marie-Tooth disease (CMT) have weaker dominant hand muscles. Since all studies to date have included a heterogeneous group of CMT patients we decided to analyse hand strength in 43 patients with CMT1X. We recorded handedness and the MRC scores for the first dorsal interosseous and abductor pollicis brevis muscles, median and ulnar nerve compound motor action potentials and conduction velocities in dominant and non-dominant hands. Twenty-two CMT1X patients (51%) had a weaker dominant hand; none had a stronger dominant hand. Mean MRC scores were significantly higher for first dorsal interosseous and abductor pollicis brevis in non-dominant hands compared to dominant hands. Median nerve compound motor action potentials were significantly reduced in dominant compared to non-dominant hands. We conclude that the dominant hand is weaker than the non-dominant hand in patients with CMT1X.

High prevalence of distal sensory polyneuropathy in antiretroviral-treated and untreated people with HIV in Tanzania

OBJECTIVES

To describe the prevalence of distal sensory polyneuropathy (DSP), a complication of both advanced HIV disease and of antiretroviral therapy (ART), amongst Tanzanians with HIV, on and off ART (including stavudine) with CD4 counts above and below 200 cells/μl.

METHODS

We recruited participants attending ART clinic into four groups: >6 months ART exposure and (i) CD4 < 200 cells/μl or (ii) CD4 > 200 cells/μl (ART/CD4 < 200 and ART/CD4 > 200, respectively); ART-naïve and (iii) CD4 < 200 cells/μl or iv)CD4 > 200 cells/μl (noART/CD4 < 200 and noART/CD4 > 200, respectively). Primary outcome was DSP, as defined by presence of at least one symptom and one sign.

RESULTS

Of 326 evaluable participants, 81 (32 men, median age 38 years, median CD4 142 cells/μl) were enrolled in the ART/CD4 < 200 group, 78 (17 men, median age 37 years, median CD4 345 cells/μl) in ART/CD4 > 200, 81 (30 men, median age 37 years, median CD4 128 cells/μl) in noART/CD4 < 200 and 86 (22 men, median age 33 years, median CD4 446 cells/μl) in noART/CD4 > 200. Numbness was the most commonly reported symptom. DSP prevalence ranged from 43.2% in ART/CD4 < 200 to 20.9% in noART/CD4 > 200. DSP was more common among men (adjusted odds ratio [aOR] 1.9, 95% confidence interval [CI] 1.2-3.3) and older participants (aOR 2.7, 95% CI 1.1-6.2 for age 40 + vs. <30 years).

CONCLUSION

Distal sensory polyneuropathy is common amongst those attending this clinic, even those with no ART exposure and a CD4 count above 200 cells/μl. Stavudine and didanosine expose HIV-infected patients to an additional avoidable risk of DSP. Access to non-neurotoxic ART regimes as well as earlier HIV diagnosis and initiation of ART is needed.

The FKBP5-gene in depression and treatment response--an association study in the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) Cohort

BACKGROUND

In a recent study of several antidepressant drugs in hospitalized, non-Hispanic White patients, Binder et al. reported association of markers located within the FKBP5 gene with treatment response after 2 and 5 weeks. Individuals homozygous for the TT-genotype at one of the markers (rs1360780) reported more depressive episodes and responded better to antidepressant treatment. There was no association between markers in FKBP5 and disease. The present study aimed at studying the associated FKBP5 markers in the ethnically diverse Sequenced Treatment Alternatives to Relieve Depression (STAR*D) sample of non-hospitalized patients treated with citalopram.

METHODS

We used clinical data and DNA samples from 1809 outpatients with non-psychotic major depressive disorder (DSM-IV criteria), who received up to 14 weeks of citalopram. A subset of 1523 patients of White non-Hispanic or Black race was matched with 739 control subjects for a case-control analysis. The markers rs1360780 and rs4713916 were genotyped on the Illumina platform. TaqMan-assay was used for marker rs3800373.

RESULTS

In the case-control analysis, marker rs1360780 was significantly associated with disease status in the White non-Hispanic sample after correction for multiple testing. A significant association was also found between rs4713916 and remission. Markers rs1360780 and rs4713916 were in strong linkage disequilibrium in the White non-Hispanic but not in the Black population. There was no significant difference in the number of previous episodes of depression between genotypes at any of the three markers.

CONCLUSIONS

These results indicate that FKBP5 is an important target for further studies of depression and treatment response.

New insights into BDNF function in depression and anxiety

The 'neurotrophin hypothesis of depression' is based largely on correlations between stress or antidepressant treatment and down- or upregulation, respectively, of brain-derived neurotrophic factor (BDNF). Genetic disruption of the signaling pathways involving BDNF and its receptor, the tyrosine kinase TrkB, does not seem to cause depressive behaviors, but does hamper the effect of antidepressant drugs. Thus, BDNF may be a target of antidepressants, but not the sole mediator of depression or anxiety. Advances in BDNF cell biology, including its transcription through multiple promoters, trafficking and secretion, may provide new insights into its role in mood disorders. Moreover, as the precursor proBDNF and the mature protein mBDNF can elicit opposite effects on cellular functions, the impact of proBDNF and its cleavage on mood should be considered. Opposing influences of mBDNF and proBDNF on long-term potentiation and long-term depression might contribute to the dichotomy of BDNF actions on behaviors mediated by the brain stress and reward systems.

Protein kinase C activity is associated with prefrontal cortical decline in aging

Aging is associated with deficiencies in the prefrontal cortex, including working memory impairment and compromised integrity of neuronal dendrites. Although protein kinase C (PKC) is implicated in structural plasticity, and overactivation of PKC results in working memory impairments in young animals, the role of PKC in prefrontal cortical impairments in the aged has not been examined. This study provides the first evidence that PKC activity is associated with prefrontal cortical dysfunction in aging. Pharmacological inhibition of PKC with chelerythrine rescued working memory impairments in aged rats and enhanced working memory in aged rhesus monkeys. Improvement correlated with age, with older monkeys demonstrating a greater degree of improvement following PKC inhibition. Furthermore, PKC activity within the prefrontal cortex was inversely correlated with the length of basal dendrites of prefrontal cortical neurons, as well as with working memory performance in aged rats. Together these findings indicate that PKC is dysregulated in aged animals and that PKC inhibitors may be useful in the treatment of cognitive deficits in the elderly.

Genetic markers of suicidal ideation emerging during citalopram treatment of major depression

OBJECTIVE

Suicidal ideation is an uncommon symptom than can emerge during antidepressant treatment. The biological basis of treatment-emergent suicidal ideation is unknown. Genetic markers may shed light on the causes of treatment-emergent suicidal ideation and help identify individuals at high risk who may benefit from closer monitoring, alternative treatments, or specialty care.

METHOD

A clinically representative cohort of outpatients with major depressive disorder who enrolled in the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) trial were treated with citalopram under a standard protocol for up to 14 weeks. DNA samples from 1,915 participants were genotyped for 768 single-nucleotide polymorphisms in 68 candidate genes. Allele and genotype frequencies were compared between the 120 participants who developed treatment-emergent suicidal ideation and those who did not.

RESULTS

Two markers were significantly associated with treatment-emergent suicidal ideation in this sample (marker rs4825476, p=0.0000784, odds ratio=1.94; permutation p=0.01; marker rs2518224, p=0.0000243, odds ratio=8.23; permutation p=0.003). These markers reside within the genes GRIA3 and GRIK2, respectively, both of which encode ionotropic glutamate receptors.

CONCLUSIONS

Markers within GRIK2 and GRIA3 were associated with treatment-emergent suicidal ideation during citalopram therapy. If replicated, these findings may shed light on the biological basis of this potentially dangerous adverse event and help identify patients at increased risk.

Association of GRIK4 with outcome of antidepressant treatment in the STAR*D cohort

OBJECTIVE

An initial pharmacogenetic study of the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) clinical trial reported an association between genetic variation in the HTR2A gene and outcome of citalopram treatment. By design, the study analyzed only those markers that showed reproducible association in the first wave of genotypes (comprising 1,297 patients) in the complete cohort of patients. The purpose of the present study was to utilize a second wave of genotype results, for a more powerful analysis, in the complete cohort of patients with available deoxyribonucleic acid (DNA) samples.

METHOD

The authors tested the association between treatment response and 768 markers that were genotyped in the full set of 1,816 eligible patients from the STAR*D cohort. In order to control for multiple testing, the subjects were divided into two study groups: discovery and replication.

RESULTS

In addition to the previously identified marker in the HTR2A gene, a new marker (rs1954787) in the GRIK4 gene, which codes for the kainic acid-type glutamate receptor KA1, was observed. The effect size of the GRIK4 marker alone was modest, but homozygote carriers of the treatment-response-associated marker alleles of both the GRIK4 and HTR2A genes were 23% less likely to experience nonresponse to treatment relative to participants who did not carry any of these marker alleles.

CONCLUSIONS

The findings demonstrate that genetic variation in a kainic acid-type glutamate receptor is reproducibly associated with response to the antidepressant citalopram. This finding suggests that the glutamate system plays an important role in modulating response to selective serotonin reuptake inhibitors (SSRIs).

Association between a functional serotonin transporter promoter polymorphism and citalopram treatment in adult outpatients with major depression

CONTEXT

The HTTLPR, a functional polymorphism of the serotonin transporter gene solute carrier family 6 (neurotransmitter transporter, serotonin), member 4 (SLC6A4), promoter, affects transcription and may be involved in antidepressant drug treatment outcome, although response rates with antidepressants can be lower in patients who experience adverse effects.

OBJECTIVE

To test the hypothesis that HTTLPR is associated with treatment outcome to citalopram.

DESIGN

A clinical effectiveness trial, Sequenced Treatment Alternatives to Relieve Depression, collected DNA samples from outpatients with nonpsychotic major depressive disorder who received citalopram in the first treatment step. The triallelic HTTLPR locus was genotyped in 1775 samples to discriminate between long (L) and short (S) alleles, followed by the A > G substitution. The low-expression S and L(G) alleles were grouped together compared with the high-expression L(A) allele.

SETTING

Eighteen primary care and 23 psychiatric care sites across the United States.

PARTICIPANTS

Ages 18 to 75 years, meeting criteria for single or recurrent nonpsychotic major depression.

MAIN OUTCOME MEASURES

Categorical response, remission, tolerance, and adverse effect burden.

RESULTS

Expression-based grouping produced a significant finding of association between the L(A) allele and adverse effect burden in the entire sample (P = .004 [genotype frequency]; P < .001 [allele frequency]). To control for bias from population stratification, a white American subsample was analyzed. A lesser adverse effect burden was associated with L(A)L(A) genotype frequency (P = .03) or L(A) allele frequency (P = .007). These findings in white patients did not hold when the L allele was undifferentiated. No association was observed between treatment outcome phenotypes and HTTLPR. Development of diarrhea and the presence of the low-expression S or L(G) alleles were the strongest risk factors associated with adverse effect burden.

CONCLUSIONS

The HTTLPR polymorphism is associated with citalopram adverse effects. Because the L(A) allele confers increased SLC6A4 transcription, increased serotonin transporter levels in brain and other tissues may lead to fewer adverse effects for antidepressant medications that target the transporter.