The genetics of early-onset bipolar disorder: A systematic review

Socio-economic status, functioning and cognition in young versus adult patients newly diagnosed with bipolar disorder and their unaffected relatives; results from a cross-sectional study

BACKGROUND

Bipolar disorders (BD) figures on top of the World Health Organization classification of disabling disorders. It is unclear if there are socioeconomic, functioning, and cognition differences in young patients newly diagnosed with BD and whether these are different for young and adult patients newly diagnosed with BD. Understanding these differences is important for tailored treatment and support.

METHODS

Participant groups included 401 patients newly diagnosed with BD, 145 of their unaffected first-degree relatives (UR) and 209 healthy control individuals (HC). First, we compared socio-economic status, functioning and cognition between young patients newly diagnosed with BD (150), UR (61) and HC (92) (15-25 years) and adult patients newly diagnosed with BD (251), UR (84) and HC (117) (>25 years), respectively. Second, within patients, we compared functioning and cognition between young and adult patients newly diagnosed with BD.

RESULTS

In both participant groups, patients newly diagnosed with BD, and to a lesser degree UR, had lower socio-economic status and impaired functioning and cognition compared with HC. Further, young patients newly diagnosed with BD were less functionally impaired, than adults newly diagnosed with BD, whereas cognition did not differ between groups.

LIMITATIONS

Applied tools for assessments of functioning and cognition are not validated below age 18.

CONCLUSIONS

Overall, lower socio-economic status and impaired functioning and cognition were found both in young and adult patients newly diagnosed with BD and their UR compared with young and adult HC, respectively. Young patients were less functionally impaired than adults, but cognition was similarly impaired.

Admixture Analysis of Age of Onset in Bipolar Disorder and Impact of Anxiety Comorbidity

BACKGROUND

 The present study aimed to examine clinical differences between subjects with early-onset (<21 years) and adult-onset (>30 years) bipolar I disorder, in particular, in relation to anxiety comorbidity.

METHOD

Subjects were selected from a cohort of 161 consecutive patients with bipolar disorder type I as diagnosed by the Structured Clinical Interview for DSM Disorder (SCID-I). Clinical characteristics and axis I comorbidity were compared between those whose illness first emerged before the age of 21 years (n=58) and those whose first episode occurred after the age of 30 years (n=27). Psychopathology was assessed using the 18-item version of the Brief Psychiatric Rating Scale (BPRS). The frequency of delusions, hallucinations, and formal thought disorders was evaluated with the SCID-I. Overall, social and occupational functioning was assessed by the Global Assessment of Functioning (GAF).

RESULTS

Most subjects with early-onset bipolar disorder were males, had panic disorder and substance abuse comorbidity, longer duration of illness, exhibited mood-incongruent delusions, and presented with a mixed episode at onset more frequently than the later adult-onset subjects. Mixed mania at the first episode of illness and lifetime panic disorder comorbidity predicted mixed polarity at the first hospitalization episode in the early-onset subjects.

CONCLUSIONS

Overall, early age at onset seems to delineate a distinct bipolar I disorder subtype characterized by a greater likelihood of mixed episodes, lifetime panic disorder comorbidity, and schizophrenia-like delusions.

Did the human genome project affect research on Schizophrenia?

The Human Genome Project was undertaken primarily to discover genetic causes and better treatments for human diseases. Schizophrenia was targeted since three of the project`s principal architects had a personal interest and also because, based on family, adoption, and twin studies, schizophrenia was widely believed to be a genetic disorder. Extensive studies using linkage analysis, candidate genes, genome wide association studies [GWAS], copy number variants, exome sequencing and other approaches have failed to identify causal genes. Instead, they identified almost 300 single nucleotide polymorphisms [SNPs] associated with altered risks of developing schizophrenia as well as some rare variants associated with increased risk in a small number of individuals. Risk genes play a role in the clinical expression of most diseases but do not cause the disease in the absence of other factors. Increasingly, observers question whether schizophrenia is strictly a genetic disorder. Beginning in 1996 NIMH began shifting its research resources from clinical studies to basic research based on the promise of the Human Genome Project. Consequently, three decades later NIMH's genetics investment has yielded almost nothing clinically useful for individuals currently affected. It is time to review NIMH`s schizophrenia research portfolio.

Mapping the global, regional and national burden of bipolar disorder from 1990 to 2019: trend analysis on the Global Burden of Disease Study 2019

BACKGROUND

Data on trends in the epidemiological burden of bipolar disorder are scarce.

AIMS

To provide an overview of trends in bipolar disorder burden from 1990 to 2019.

METHOD

Revisiting the Global Burden of Disease Study 2019, we analysed the number of cases, calculated the age-standardised rate (per 100 000 population) and estimated annual percentage change (EAPC) of incidence, prevalence and years lived with disability (YLDs) for bipolar disorder from 1990 to 2019. The independent effects of age, period and cohort were estimated by the age-period-cohort modelling.

RESULTS

Globally, the bipolar disorder-related prevalent cases, incident cases and number of YLDs all increased from 1990 to 2019. Regionally, the World Health Organization Region of the Americas accounted for the highest estimated YLD number and rate, with the highest age-standardised prevalence rate in 1990 and 2019 and highest EAPC of prevalence. By sociodemographic index (SDI) quintiles, all five SDI regions saw an increase in estimated incident cases. Nationally, New Zealand reported the highest age-standardised rate of incidence, prevalence and YLDs in 1990 and 2019. The most prominent age effect on incidence rate was in those aged 15-19 years. Decreased effects of period on incidence, prevalence and YLD rates was observed overall and in females, not in males. The incidence, prevalence and YLD rates showed an unfavourable trend in the younger cohorts born after 1990, with males reporting a higher cohort risk than females.

CONCLUSIONS

From 1990 to 2019, the overall trend of bipolar disorder burden presents regional and national variations and differs by age, sex, period and cohort.

Paediatric bipolar disorder and its controversy

OBJECTIVES

Paediatric bipolar disorder - bipolar disorder occurring in prepubertal children - is a diagnosis subject to considerable controversy. Whilst historically considered to be very rare, proponents since the 1990s have argued that mania can present differently in children and, as such, is much more common than previously thought. Such proposals raise questions about the validity of proposed phenotypes and potential risks of iatrogenic harm.

METHODS

I critically examine the construct of paediatric bipolar disorder using Robins and Guze's (1970, American Journal of Psychiatry126, 983-987) influential criteria for the validity of a psychiatric diagnosis. I review, in turn, evidence relating to its clinical description, delimitation from other conditions, follow-up studies, family studies, laboratory studies, and treatment response.

RESULTS

Across domains, existing research highlights significant challenges establishing the diagnosis. This includes significant heterogeneity in operationalising criteria for children; variable or poor inter-rater reliability; difficulty distinguishing paediatric bipolar disorder from other conditions; large differences in rates of diagnosis between the United States of America and other countries; limited evidence of continuity with adult forms; and a lack of evidence for proposed paediatric phenotypes in children at genetic high-risk of the condition. Laboratory and treatment studies are limited, but also do not provide support for the construct.

CONCLUSIONS

Evidence for the more widespread existence of paediatric bipolar disorder and its various proposed phenotypes remains weak. The ongoing popularity of the diagnosis, most evident in America, may reflect social pressures and broader limitations in psychiatric nosology. The uncertainty around the diagnosis highlights the need for careful longitudinal assessment of children potentially affected.

Factors associated with onset-age in major affective disorders

BACKGROUND

Research findings on factors associated with onset-age (OA) with bipolar (BD) and major depressive disorders (MDD) have been inconsistent, but often indicate greater morbidity following early OA.

METHODS

We considered factors associated with OA in 1033 carefully evaluated, systematically followed mood disorder subjects with DSM-5 BD (n = 505) or MDD (n = 528), comparing rates of descriptive and clinical characteristics following early (age <18), intermediate (18-40), or later onset (≥40 years), as well as regressing selected measures versus OA. Exposure time (years ill) was matched among these subgroups.

RESULTS

As hypothesized, many features were associated with early OA: familial psychiatric illness, including BD, greater maternal age, early sexual abuse, nondepressive first episodes, co-occurring ADHD, suicide attempts and violent suicidal behavior, abuse of alcohol or drugs, smoking, and unemployment. Other features increased consistently with later OA: %-time-depressed (in BD and MDD, women and men), as well as depressions/year and intake ratings of depression, educational levels, co-occurring medical disorders, rates of marriage and number of children.

CONCLUSIONS

OA averaged 7.5 years earlier in BD versus MDD (30.7 vs. 38.2). Some OA-associated measures may reflect maturation. Associations with family history and suicidal risk with earlier OA were expected; increases of time-depressed in both BD and MDD with later OA were not. We conclude that associations of OA with later morbidity are complex and not unidirectional but may be clinically useful.

Composite immune marker scores associated with severe mental disorders and illness course

Background

Low-grade inflammation has been implicated in the pathophysiology of severe mental disorders (SMDs) and a link between immune activation and clinical characteristics is suggested. However, few studies have investigated how patterns across immune markers are related to diagnosis and illness course.

Methods

A total of 948 participants with a diagnosis of schizophrenia (SCZ, N = 602) or bipolar (BD, N = 346) spectrum disorder, and 814 healthy controls (HC) were included. Twenty-five immune markers comprising cell adhesion molecules (CAMs), interleukin (IL)-18-system factors, defensins, chemokines and other markers, related to neuroinflammation, blood-brain barrier (BBB) function, inflammasome activation and immune cell orchestration were analyzed. Eight immune principal component (PC) scores were constructed by PC Analysis (PCA) and applied in general linear models with diagnosis and illness course characteristics.

Results

Three PC scores were significantly associated with a SCZ and/or BD diagnosis (HC reference), with largest, however small, effect sizes of scores based on CAMs, BBB markers and defensins (p < 0.001, partial η² = 0.02–0.03). Number of psychotic episodes per year in SCZ was associated with a PC score based on IL-18 system markers and the potential neuroprotective cytokine A proliferation-inducing ligand (p = 0.006, partial η² = 0.071).

Conclusion

Analyses of composite immune markers scores identified specific patterns suggesting CAMs-mediated BBB dysregulation pathways associated with SMDs and interrelated pro-inflammatory and neuronal integrity processes associated with severity of illness course. This suggests a complex pattern of immune pathways involved in SMDs and SCZ illness course.

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Composite score of VCAM-1, ICAM-1, NCAD and IL-18BP associated with SCZ and BD.

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Composite score of MadCAM-1 and BD-1 associated with SCZ and BD.

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Composite score of S100B, furin, HNP1-3 and BD-1 associated with BD.

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Composite score of APRIL and IL-18R markers associated with psychotic episode rate.

Novel splice‑site variants c.393G>A, c.278_2A>G in exon 2 and Q705K variant in exon 3 of NLRP3 gene are associated with bipolar I disorder

NOD‑like receptor pyrin domain‑containing 3 (NLRP3) has been considered to play a crucial role in triggering the host's immune and inflammatory responses. Genetic variants are critical determinants of interindividual variances in inflammatory responses and clinical outcomes. The role of NLRP3 gene variations in bipolar I (BPI) disorder, which is known to include genetic factors in its aetiology, has not been previously reported, at least to the best of our knowledge. The present study aimed to determine the role and frequency ofta exon 2 and exon 3 variants of NLRP3 in BPI disorder and to evaluate the association between different phenotypic traits. A case‑control study with 123 patients and 107 healthy controls was conducted to investigate the association of variants identified in the exon 2 and exon 3 regions of NLRP3, with the risk of BPI. Regions of interest were sequenced using a PCR‑based Sanger sequencing method. Three BPI‑related variants were identified. The genotype Q705K CA was detected more frequently in BPI patients, as compared to the control group [P<0.001; odds ratio (OR), 0.202; 95% confidence interval (CI), 0.080‑0.508]. In addition, two novel splice‑site variants (c.393G>A and c.278_2A>G) that, to the best of our knowledge, have not been previously reported in any database, were detected only in the BPI patient group [P<0.001; OR, 0.846; 95% CI, 0.784‑0.912; P<0.001; OR, 0.886; 95% CI, 0.832‑0.944, respectively]. There was no significant association between the Q795K variant and phenotypic traits (P>0.05). However, there was a significant association between those carrying the heterozygous c.393G>A variant and a positive family history (P=0.043). It was also observed that those with the heterozygous c.278‑2A>G variant presented with a significantly early‑onset (P=0.003). On the whole, the data of the present study suggested that NLRP3 plays a crucial role in the pathogenesis of BPI and may be a potential risk factor. However, further functional studies and repeated studies in other populations are required to properly comprehend the roles of the NLRP3 variants in the risk of developing BPI.

Prevalence and correlates of childhood-onset bipolar disorder among adolescents

AIM

Early-onset bipolar disorder (BD) is associated with a more severe illness as well as a number of clinical factors among adults. Early-onset can be categorized as childhood- (age < 13) or adolescent- (age ≥ 13) onset, with the two displaying different clinical profiles. We set out to examine differences in clinical, and familial characteristics among adolescents with childhood- versus adolescent-onset BD.

METHODS

The study included 195 adolescents with BD, ages 14-18 years. Age of onset was determined retrospectively by self-report. Participants completed the semi-structured K-SADS-PL diagnostic interviews along with self-reported dimensional scales. Analyses examined between-group differences for clinical and familial variables. Variables associated with age of onset at p < 0.1 in univariate analyses were evaluated in a logistic regression model.

RESULTS

Approximately one-fifth of participants had childhood-onset BD (n = 35; 17.9%). A number of clinical and familial factors were significantly associated with childhood-onset BD. However, there were no significant differences in depressive and manic symptom severity. In multivariate analyses, the variables most strongly associated with childhood-onset were police contact, and family history of suicidal ideation. Smoking and psychiatric hospitalization were associated with adolescent-onset.

CONCLUSIONS

In this large clinical sample of adolescents with BD, one-fifth reported childhood-onset BD. Correlates of childhood-onset generally aligned with those observed in the literature. Future research is warranted to better understand the genetic and environmental implications of high familial loading of psychopathology associated with childhood-onset, and to integrate age-related treatment and prevention strategies.

Genetic polymorphisms influencing response to lithium in early-onset Bipolar disorder from south India

OBJECTIVES

Early-onset Bipolar disorder (EOBD), has a more malignant course with high recurrence risk and there is a need for population-specific pharmaco-genomic study.

METHODS

This study is a prospective and retrospective observational study. Both newly diagnosed patients and those on follow-up with a diagnosis of bipolar I disorder with onset before 18 years of age and on lithium prophylaxis as part of treatment-as-usual were recruited for the study. Response to treatment was assessed at the end of two years follow up using ALDA scale. Ten single nucleotide polymorphisms associated with treatment response based on previous studies were chosen for analysis.

RESULTS

Of 162 who had EOBD, sixty-four fulfilled inclusion criteria and fifty-seven completed the study. TT and TG genotypes of rs75222709 on AL157359.3 gene were found to be significantly different between non-responders(N = 43) and healthy controls (N = 220). The frequency of the GA genotype of the single nucleotide polymorphism rs17204573 of the RORA (Retinoic Acid related orphan receptor alpha) gene was significantly lower among subjects (27.3%, N = 54) as compared to controls (42.9%, OR:0.5, CI: 0.26-0.96, p value 0.035). However, the significance of both disappeared after Bonferroni correction. Among clinical factors female gender was significantly associated with lithium non-response.

CONCLUSION

Although conducting pharmaco-genomic studies with large sample size is a challenge for low and middle-income countries, future studies can help improve the long-term outcome of youth with EOBD.

Association between early-onset affective disorders and hypothyroidism in a larger number of psychiatric drug-free patients

AIMS

We aimed to assess the association between early onset of affective disorders and hypothyroidism in a larger number of psychiatric drug-free patients with bipolar disorder (BD) or major depressive disorder (MDD).

METHODS

Early onset of affective disorders was defined as BD and MDD developed before the age of 22 years. The hypothyroidism hierarchy were diagnosed biochemically and included subclinical and overt hypothyroidism in this study. Demographic and clinical data including diagnosis, illness duration and thyroid function parameters (TSH, T4, FT4, T3 and FT3) at admission were collected from patients' records. Adjusted odds ratio (OR) and 95% confidence interval (CI), which were estimated by logistic regression model, were used to assess the association between early-onset affective disorder and hypothyroidism.

RESULTS

The prevalence of hypothyroidism in early-onset affective disorders was higher than that in late-onset patients (in BD, 9.4% vs. 6.2%, χ² = 6.020, P = 0.014; and in MDD 12.7% vs. 6.6%, χ² = 13.295, P < 0.001). Early-onset affective disorders were 2.097 times (95% CI: 1.409-3.123) more likely to have hypothyroidism compared with late-onset patients, after adjustment for age, gender, duration of illness and mood episode (adjusted OR: 1.965, 95% CI: 1.198-3.221 in BD, and adjusted OR: 2.831, 95% CI: 1.378-5.817 in MDD, respectively).

LIMITATION

Because of the cross-sectional design of this study, we were unable to sort out causality between early-onset affective disorders and hypothyroidism.

CONCLUSION

Early-onset affective disorder may be associated with higher prevalence of hypothyroidism.

CADPS functional mutations in patients with bipolar disorder increase the sensitivity to stress

Bipolar disorder is a severe and chronic psychiatric disease resulting from a combination of genetic and environmental risk factors. Here, we identified a significant higher mutation rate in a gene encoding the calcium-dependent activator protein for secretion (CADPS) in 132 individuals with bipolar disorder, when compared to 184 unaffected controls or to 21,070 non-psychiatric and non-Finnish European subjects from the Exome Aggregation Consortium. We found that most of these variants resulted either in a lower abundance or a partial impairment in one of the basic functions of CADPS in regulating neuronal exocytosis, synaptic plasticity and vesicular transporter-dependent uptake of catecholamines. Heterozygous mutant mice for Cadps^+/- revealed that a decreased level of CADPS leads to manic-like behaviours, changes in BDNF level and a hypersensitivity to stress. This was consistent with more childhood trauma reported in families with mutation in CADPS, and more specifically in mutated individuals. Furthermore, hyperactivity observed in mutant animals was rescued by the mood-stabilizing drug lithium. Overall, our results suggest that dysfunction in calcium-dependent vesicular exocytosis may increase the sensitivity to environmental stressors enhancing the risk of developing bipolar disorder.

Candidate risk genes for bipolar disorder are highly conserved during evolution and highly interconnected

OBJECTIVES

Bipolar disorder (BPD) is a highly heritable psychiatric disorder whose genetic complexity and pathogenetic mechanisms are still being unraveled. The main goal of this work was to characterize BPD risk-gene candidates (identified by Nurnberger et al., JAMA Psychiatry 71:657, 2014, and Stahl et al., Nat. Genet. 51:793, 2019) with respect to their evolutionary conservation, associated phenotypes, and extent of gene-gene interactions.

METHODS

Database searches and BLAST were used to identify homologous counterparts of human BPD risk genes in C. elegans, zebrafish, and Drosophila. Phenotypes associated with the C. elegans genes were annotated and searched. With GeneMANIA, we characterized and quantified gene-gene interactions among members of the BPD gene set in comparison to randomly chosen gene sets of the same size.

RESULTS

BPD risk genes are highly conserved across species and are enriched for essential genes and genes associated with lethality and altered life span. They are significantly more interactive with each other in comparison to random genes. We identified syntenic blocks of risk genes, which provided potential insights into molecular pathways and co-morbidities associated with BPD including coronary disease, obesity, and decreased life expectancy.

CONCLUSIONS

BPD risk genes appear to be special in terms of their degree of conservation, interconnectedness, and pleiotropic effects that extend beyond a role in brain function. Key hub genes or pleiotropic regulatory components may represent attractive targets for future drug discovery.

Genome-wide association study of early-onset bipolar I disorder in the Han Taiwanese population

The search for susceptibility genes underlying the heterogeneous bipolar disorder has been inconclusive, often with irreproducible results. There is a hope that narrowing the phenotypes will increase the power of genetic analysis. Early-onset bipolar disorder is thought to be a genetically homogeneous subtype with greater symptom severity. We conducted a genome-wide association study (GWAS) for this subtype in bipolar I (BPI) disorder. Study participants included 1779 patients of Han Chinese descent with BPI disorder recruited by the Taiwan Bipolar Consortium. We conducted phenotype assessment using the Chinese version of the Schedules for Clinical Assessment in Neuropsychiatry and prepared a life chart with graphic depiction of lifetime clinical course for each of the BPI patient recruited. The assessment of onset age was based on this life chart with early onset defined as ≤20 years of age. We performed GWAS in a discovery group of 516 early-onset and 790 non-early-onset BPI patients, followed by a replication study in an independent group of 153 early-onset and 320 non-early-onset BPI patients and a meta-analysis with these two groups. The SNP rs11127876, located in the intron of CADM2, showed association with early-onset BPI in the discovery cohort (P = 7.04 × 10^-8) and in the test of replication (P = 0.0354). After meta-analysis, this SNP was demonstrated to be a new genetic locus in CADM2 gene associated with early-onset BPI disorder (P = 5.19 × 10^-8).

Astroglial cells as neuroendocrine targets in forebrain development: Implications for sex differences in psychiatric disease

Astroglial cells are the most abundant cell type in the mammalian brain. They are implicated in almost every aspect of brain physiology, including maintaining homeostasis, building and maintaining the blood brain barrier, and the development and maturation of neuronal networks. Critically, astroglia also express receptors for gonadal sex hormones, respond rapidly to gonadal hormones, and are able to synthesize hormones. Thus, they are positioned to guide and mediate sexual differentiation of the brain, particularly neuronal networks in typical and pathological conditions. In this review, we describe astroglial involvement in the organization and development of the brain, and consider known sex differences in astroglial responses to understand how astroglial cell-mediated organization may play a role in forebrain sexual dimorphisms in human populations. Finally, we consider how sexually dimorphic astroglial responses and functions in development may lead to sex differences in vulnerability for neuropsychiatric disorders.

Familial aggregation analysis of cognitive performance in early-onset bipolar disorder

We analysed the familial aggregation (familiality) of cognitive dimensions and explored their role as liability markers for early-onset bipolar disorder (EOBD). The sample comprised 99 subjects from 26 families, each with an offspring diagnosed with EOBD. Four cognitive dimensions were assessed: reasoning skills; attention and working memory; memory; and executive functions. Their familiality was investigated in the total sample and in a subset of healthy relatives. The intra-family resemblance score (IRS), a family-based index of the similarity of cognitive performance among family members, was calculated. Familiality was detected for the attention and working memory (AW) dimension in the total sample (ICC = 0.37, p = 0.0004) and in the subsample of healthy relatives (ICC = 0.37, p = 0.016). The IRS reflected that there are families with similar AW mean scores (either high or low) and families with heterogeneous scores. Families with the most common background for the AW dimension (IRS > 0) were selected and dichotomized in two groups according to the mean family AW score. This allowed differentiating families whose members had similar high scores than those with similar low scores: both patients (t = - 4.82, p = 0.0005) and relatives (t = - 5.04, p < 0.0001) of the two groups differed in their AW scores. AW dimension showed familial aggregation, suggesting its putative role as a familial vulnerability marker for EOBD. The IRS estimation allowed the identification of families with homogeneous scores for this dimension. This represents a first step towards the investigation of the underlying mechanisms of AW dimension and the identification of etiological subgroups.

Genetic susceptibility to nicotine addiction: Advances and shortcomings in our understanding of the CHRNA5/A3/B4 gene cluster contribution

Over the last decade, robust human genetic findings have been instrumental in elucidating the heritable basis of nicotine addiction (NA). They highlight coding and synonymous polymorphisms in a cluster on chromosome 15, encompassing the CHRNA5, CHRNA3 and CHRNB4 genes, coding for three subunits of the nicotinic acetylcholine receptor (nAChR). They have inspired an important number of preclinical studies, and will hopefully lead to the definition of novel drug targets for treating NA. Here, we review these candidate gene and genome-wide association studies (GWAS) and their direct implication in human brain function and NA-related phenotypes. We continue with a description of preclinical work in transgenic rodents that has led to a mechanistic understanding of several of the genetic hits. We also highlight important issues with regards to CHRNA3 and CHRNB4 where we are still lacking a dissection of their role in NA, including even in preclinical models. We further emphasize the use of human induced pluripotent stem cell-derived models for the analysis of synonymous and intronic variants on a human genomic background. Finally, we indicate potential avenues to further our understanding of the role of this human genetic variation. This article is part of the special issue on 'Contemporary Advances in Nicotine Neuropharmacology'.

Insulin resistance takes center stage: a new paradigm in the progression of bipolar disorder

Bipolar Disorder (BD) is a major psychiatric illness affecting up to 5% of the population. BD can progress over time to a chronic "neuroprogressive" course with cognitive and functional impairment. Currently, there are no validated predictors indicating which patients will develop a neuroprogressive course and there are no specific treatments. This review presents data supporting a novel hypothesis on the mechanisms underlying bipolar neuroprogression. Insulin resistance (IR) is present in 52% of BD patients and is associated with chronic course, treatment nonresponse, adverse brain changes and cognitive impairment. Further, bipolar morbidity increases 12-fold following the onset of IR indicating that IR may modify disease progression. I review evidence that IR is a testable and treatable modifying factor in neuroprogression and that reversing IR may be an efficient (and perhaps the only) means of obtaining remission in some patients. I draw a parallel with Helicobacter pylori in peptic ulcer disease (a novel mechanism that brought together two previously unrelated phenomena that uncovered a new treatment approach). This model of bipolar progression combines shared dysregulated mechanisms between IR and BD, allowing for early screening, case finding, and monitoring for neuroprogression, with the potential for intervention that could prevent advanced bipolar illness. KEY MESSAGES Neuroprogression in bipolar disorder is defined by a more severe form of illness and poor outcome. Currently, there are no validated predictors of neuroprogression, which could help inform treatment and improve prognosis. Insulin resistance is present in more than half of all bipolar patients and is associated with a chronic course of illness, lack of response to mood stabilizing treatment, cognitive impairment and poor functional outcomes. Insulin resistance may modify the course of bipolar disorder and promote neuroprogression. Insulin resistance may be a testable and potentially modifiable risk factor for neuroprogression in bipolar disorder.

Investigating polygenic burden in age at disease onset in bipolar disorder: Findings from an international multicentric study

OBJECTIVES

Bipolar disorder (BD) with early disease onset is associated with an unfavorable clinical outcome and constitutes a clinically and biologically homogenous subgroup within the heterogeneous BD spectrum. Previous studies have found an accumulation of early age at onset (AAO) in BD families and have therefore hypothesized that there is a larger genetic contribution to the early-onset cases than to late onset BD. To investigate the genetic background of this subphenotype, we evaluated whether an increased polygenic burden of BD- and schizophrenia (SCZ)-associated risk variants is associated with an earlier AAO in BD patients.

METHODS

A total of 1995 BD type 1 patients from the Consortium of Lithium Genetics (ConLiGen), PsyCourse and Bonn-Mannheim samples were genotyped and their BD and SCZ polygenic risk scores (PRSs) were calculated using the summary statistics of the Psychiatric Genomics Consortium as a training data set. AAO was either separated into onset groups of clinical interest (childhood and adolescence [≤18 years] vs adulthood [>18 years]) or considered as a continuous measure. The associations between BD- and SCZ-PRSs and AAO were evaluated with regression models.

RESULTS

BD- and SCZ-PRSs were not significantly associated with age at disease onset. Results remained the same when analyses were stratified by site of recruitment.

CONCLUSIONS

The current study is the largest conducted so far to investigate the association between the cumulative BD and SCZ polygenic risk and AAO in BD patients. The reported negative results suggest that such a polygenic influence, if there is any, is not large, and highlight the importance of conducting further, larger scale studies to obtain more information on the genetic architecture of this clinically relevant phenotype.

Association between genetic variation in the myo-inositol monophosphatase 2 (IMPA2) gene and age at onset of bipolar disorder

INTRODUCTION

The age at onset of bipolar disorder (BD) has significant implications for severity, duration of affective episodes, response to treatment, and psychiatric comorbidities. It has been suggested that early-onset BD (EO-BD) could represent a clinically distinct subtype with probable genetic risk factors different from those of late-onset BD (LO-BD). To date, several genes have been associated with BD risk but few studies have investigated the genetic differences between EO-BD and LO-BD. The aim of this study was to evaluate if variants of the gene coding for myo-inositol monophosphatase (IMPA2) are linked to age at onset of BD.

METHOD

235 bipolar patients were recruited and assessed. The final sample consisting of 192 euthymic individuals, was compared according to the age at onset. Polymorphisms were genotyped in the IMPA2 gene (rs669838, rs1020294, rs1250171, and rs630110). Early-onset was defined by the appearance of a first affective episode before the age of 18.

RESULTS

The analyses showed that in the genotype distribution rs1020294 (p = .01) and rs1250171 (p = .01) were associated with the age at onset. The significant effect remained only in the rs1020294 SNP in which G carriers were more likely to debut later compared to patients presenting the AA genotype (p = .002; OR = 9.57, CI95%[2.37-38.64]). The results also showed that EO-BD tended to experience more alcohol misuse (p = .003; OR = .197, CI95%[.07-.58]) compared to LO-BD.

CONCLUSIONS

Our results provide evidence for genetic differences between EO-BD and LO-BD at the IMPA2 gene as well as clinical differences between subgroups with therapeutic implications.

Potential biomarkers for bipolar disorder: Where do we stand?

Bipolar disorder (BD) is a severe, recurrent mood disorder, associated with a significant morbidity and mortality, with high rates of suicides and medical comorbidities. There is a high risk of mood disorders among the first-degree relatives of patients with BD. In the current clinical practice, the diagnosis of BD is made by history taking, interview and behavioural observations, thereby lacking an objective, biological validation. This approach may result in underdiagnosis, misdiagnosis and eventually poorer outcomes. Due to the heterogeneity of BD, the possibility of developing a single, specific biomarker is still remote; however, there is a set of promising biomarkers which may serve as predictive, prognostic or treatment markers in the future. The review presents a critical appraisal and update on some of the most promising candidates for biomarkers, namely, neuroimaging markers, peripheral biomarkers and genetic markers, including a brief discussion on cognitive endophenotypes as indicative of genetic risk. The lessons learnt from other fields and specialties in medicine need to be applied to psychiatry to translate the knowledge from ‘bench to bedside’ by means of clinically useful biomarkers. Overall, the biomarkers may help in pushing the shift towards personalized medicine for psychiatric patients.

Solar insolation in springtime influences age of onset of bipolar I disorder

OBJECTIVE

To confirm prior findings that the larger the maximum monthly increase in solar insolation in springtime, the younger the age of onset of bipolar disorder.

METHOD

Data were collected from 5536 patients at 50 sites in 32 countries on six continents. Onset occurred at 456 locations in 57 countries. Variables included solar insolation, birth-cohort, family history, polarity of first episode and country physician density.

RESULTS

There was a significant, inverse association between the maximum monthly increase in solar insolation at the onset location, and the age of onset. This effect was reduced in those without a family history of mood disorders and with a first episode of mania rather than depression. The maximum monthly increase occurred in springtime. The youngest birth-cohort had the youngest age of onset. All prior relationships were confirmed using both the entire sample, and only the youngest birth-cohort (all estimated coefficients P < 0.001).

CONCLUSION

A large increase in springtime solar insolation may impact the onset of bipolar disorder, especially with a family history of mood disorders. Recent societal changes that affect light exposure (LED lighting, mobile devices backlit with LEDs) may influence adaptability to a springtime circadian challenge.

Genetic Risk Score Analysis in Early-Onset Bipolar Disorder

OBJECTIVE

In this study, we performed a candidate genetic risk score (GRS) analysis of early-onset bipolar disorder (BD).

METHODS

Treatment of Early Age Mania (TEAM) study enrollment and sample collection took place from 2003 to 2008. Mayo Clinic Bipolar Biobank samples were collected from 2009 to 2013. Genotyping and analyses for the present study took place from 2013 to 2014. The diagnosis of BD was based on Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision criteria. Eight single-nucleotide polymorphisms (SNPs), previously reported in genome-wide association studies to be associated with BD, were chosen for GRS analysis in early-onset bipolar disease. These SNPs map to 3 genes: CACNA1C (calcium channel, voltage-dependent, L type, alpha 1C subunit), ANK3 (ankyrin-3, node of Ranvier [ankyrin G]), and ODZ4 (teneurin transmembrane protein 4 [formerly "odz, odd Oz/10-m homolog 4 {Drosophila}, ODZ4"]). The 8 candidate SNPs were genotyped in patients from the TEAM study (n = 69); adult patients with BD (n = 732), including a subset with early-onset illness (n = 192); and healthy controls (n = 776). GRS analyses were performed to compare early-onset cases with controls. In addition, associations of early-onset BD with individual SNPs and haplotypes were explored.

RESULTS

GRS analysis revealed associations of the risk score with early-onset BD (P = .01). Gene-level haplotype analysis comparing TEAM patients with controls suggested association of early-onset BD with a CACNA1C haplotype (global test, P = .01). At the level of individual SNPs, comparison of TEAM cases with healthy controls provided nominally significant evidence for association of SNP rs10848632 in CACNA1C with early-onset BD (P = .017), which did not remain significant after correction for multiple comparisons.

CONCLUSIONS

These preliminary analyses suggest that previously identified BD risk loci, especially CACNA1C, have a role in early-onset BD, possibly with stronger effects than for late-onset BD.

Infectious and immunogenetic factors in bipolar disorder

OBJECTIVE

Despite the evidence supporting the association between infection and bipolar disorder (BD), the genetic vulnerability that mediates its effects has yet to be clarified. A genetic origin for the immune imbalance observed in BD, possibly involved in the mechanisms of pathogen escape, has, however, been suggested in recent studies.

METHOD

Here, we present a critical review based on a systematic literature search of articles published until December 2016 on the association between BD and infectious/immunogenetic factors.

RESULTS

We provide evidence suggesting that infectious insults could act as triggers of maladaptive immune responses in BD and that immunogenetic vulnerability may amplify the effects of such environmental risk factors, increasing susceptibility to subsequent environmental encounters. Quality of evidence was generally impaired by scarce attempt of replication, small sample sizes and lack of high-quality environmental measures.

CONCLUSION

Infection has emerged as a potential preventable cause of morbidity in BD, urging the need to better investigate components of the host-pathogen interaction in patients and at-risk subjects, and thus opening the way to novel therapeutic opportunities.

The specificity of the familial aggregation of early-onset bipolar disorder: A controlled 10-year follow-up study of offspring of parents with mood disorders

BACKGROUND

Two major sources of heterogeneity of mood disorders that have been demonstrated in clinical, family and genetic studies are the mood disorder subtype (i.e. bipolar (BPD) and major depressive disorder (MDD)) and age of onset of mood episodes. Using a prospective high-risk study design, our aims were to test the specificity of the parent-child transmission of BPD and MDD and to establish the risk of psychopathology in offspring in function of the age of onset of the parental disorder.

METHODS

Clinical information was collected on 208 probands (n=81 with BPD, n=64 with MDD, n=63 medical controls) as well as their 202 spouses and 372 children aged 6-17 years at study entry. Parents and children were directly interviewed every 3 years (mean duration of follow-up=10.6 years). Parental age of onset was dichotomized at age 21.

RESULTS

Offspring of parents with early onset BPD entailed a higher risk of BPD HR=7.9(1.8-34.6) and substance use disorders HR=5.0(1.1-21.9) than those with later onset and controls. Depressive disorders were not significantly increased in offspring regardless of parental mood disorder subtype or age of onset.

LIMITATIONS

Limited sample size, age of onset in probands was obtained retrospectively, age of onset in co-parents was not adequately documented, and a quarter of the children had no direct interview.

CONCLUSIONS

Our results provide support for the independence of familial aggregation of BPD from MDD and the heterogeneity of BPD based on patterns of onset. Future studies should further investigate correlates of early versus later onset BPD.