Anticipation in bipolar affective disorder: is age at onset a valid criterion?

Applying polygenic risk scoring for psychiatric disorders to a large family with bipolar disorder and major depressive disorder

Psychiatric disorders are thought to have a complex genetic pathology consisting of interplay of common and rare variation. Traditionally, pedigrees are used to shed light on the latter only, while here we discuss the application of polygenic risk scores to also highlight patterns of common genetic risk. We analyze polygenic risk scores for psychiatric disorders in a large pedigree (n ~ 260) in which 30% of family members suffer from major depressive disorder or bipolar disorder. Studying patterns of assortative mating and anticipation, it appears increased polygenic risk is contributed by affected individuals who married into the family, resulting in an increasing genetic risk over generations. This may explain the observation of anticipation in mood disorders, whereby onset is earlier and the severity increases over the generations of a family. Joint analyses of rare and common variation may be a powerful way to understand the familial genetics of psychiatric disorders.

Unstable repeat expansion in major psychiatric disorders: two decades on, is dynamic DNA back on the menu?

For a period in the mid-1990s, soon after the discovery of the involvement of trinucleotide repeat expansions in fragile-X syndrome (both A and E), Huntington's disease, myotonic dystrophy, and a number of hereditary ataxias, there was a clear sense that this new disease mechanism might provide answers for psychiatric disorders. Given the then failures to replicate initial genetic linkage findings for schizophrenia (SCZ) and bipolar disorder (BD), a greater emphasis was placed on the role of complex and non-Mendelian mechanisms, and repeat instability appeared to have the potential to provide adequate explanations for numerous apparently non-Mendelian features such as anticipation, incomplete penetrance, sporadic occurrence, and nonconcordance of monozygotic twins. Initial molecular studies using a ligation-based amplification method (repeat expansion detection) appeared to support the involvement of CAG•CTG repeat expansion in SCZ and BD. However, subsequent studies that dissected the large repeats responsible for much of the positive signal showed that there were three main loci where CAG•CTG repeat expansion was occurring (on 13q21.33, 17q21.33-q22, and 18q21.2). None of the expansions at these loci appeared to segregate with SCZ or BD, and research into repeat expansions in psychiatric illness petered out in the early 2000s. The 13q expansion occurs within a noncoding RNA and appears to be associated with spinocerebellar ataxia 8 (SCA8), but with a still unexplained dichotomy in penetrance - either very high or very low. The 17q expansion occurs within an intron of the carbonic anhydrase-like gene, CA10. The 18q expansion is located within an intron of the TCF4 gene. Mutations in TCF4 are a known cause of Pitt-Hopkins syndrome. Also, pertinently, genome-wide association studies have shown a well-replicated association between TCF4 and SCZ. Two decades on, in 2016, it appears to be an appropriate juncture to reflect on what we have learned, and, with the arrival of newer technologies, whether there is any mileage to be made in revisiting the unstable DNA hypothesis for psychiatric illness.

Genetic anticipation in a special form of hypertrophic cardiomyopathy with sudden cardiac death in a family with 74 members across 5 generations

Hypertrophic cardiomyopathy (HCM) is the most common heritable heart disease. The genetic anticipation of HCM and its associated etiology, sudden cardiac death (SCD), remains unclear. The aim of this study was to investigate the mechanism underlying the genetic anticipation of HCM and associated SCD.An HCM family including 5 generations and 74 members was studied. Two-dimensional echocardiography was performed to diagnose HCM. The age of onset of HCM was defined as the age at first diagnosis according to hospital records. The information on SCD was confirmed by verification by ≥2 family members and a review of hospital records. Whole-genome sequencing was performed on 4 HCM subjects and 1 healthy control in the family. The identified mutations were screened in all available family members and 216 unrelated healthy controls by Sanger sequencing.The median ages of onset of HCM were 63.5, 38.5, and 18.0 years in members of the second, third, and fourth generations of the family, respectively, and the differences between the generations were significant (P < 0.001). The age at SCD also decreased with each subsequent generation (P < 0.05). In particular, among the third-generation family members, SCD occurred between 30 and 40 years of age at approximately 8 AM, whereas among the fourth-generation family members, all 5 males who experienced SCD were 16 years of age and died at approximately 8 AM. The sarcomere gene mutations MYH7-A719H and MYOZ2-L169G were detected in the HCM individuals in this pedigree. Increases in the number of mutations and the frequency of multiple gene mutations were observed in the younger generations. Moreover, a structural variant was present in the HCM phenotype-positive subjects but was absent in the HCM phenotype-negative subjects.HCM may exhibit genetic anticipation, with a decreased age of onset and increased severity in successive generations. Multiple gene mutations may contribute to genetic anticipation in HCM and thus may be of prognostic value.

Clinical characteristics of bipolar disorder: a comparative study between Argentina and the United States

BACKGROUND

Bipolar disorder presents with diverse clinical manifestations. Numerous investigators have sought to identify variables that may predict a more severe illness course.

METHODS

With the objective of studying the clinical characteristics of bipolar patients between South and North America, a comparison was performed between a sample from Argentina (n = 449) and a sample from the United States (n = 503) with respect to demographics and clinical characteristics, including presence of comorbidities.

RESULTS

The Argentinian sample had more unfavorable demographics and higher rates of prior psychiatric hospitalization and prior suicide attempt but a better social outcome. However, the sample from the United States had a higher rate of prior year rapid cycling, as well as younger bipolar disorder onset age (mean ± SD, 17.9 ± 8.4 vs. 27.1 ± 11.4 years) and more severe clinical morbidity, though there was no significant difference in terms of the total duration of the illness. Argentinian compared to American patients were taking more mood stabilizers and benzodiazepines/hypnotics, but fewer antipsychotics and other psychotropic medications, when considering patients in aggregate as well as when stratifying by illness subtype (bipolar I versus bipolar II) and by illness onset age (≤21 vs. >21 years). However, there was no significant difference in rate of antidepressant prescription between the two samples considered in aggregate.

CONCLUSIONS

Although possessing similar illness durations, these samples presented significant clinical differences and distinctive prescription patterns. Thus, though the Argentinian compared to North American patients had more unfavorable demographics, they presented a better social outcome and, in several substantive ways, more favorable illness characteristics. In both samples, early onset (age ≤ 21 years) was a marker for poor prognosis throughout the illness course, although this phenomenon appeared more robust in North America.

Depression across mood disorders: review and analysis in a clinical sample

OBJECTIVES

In this article we aimed to: (1) review literature concerning the clinical and psychopathologic characteristics of Bipolar (BP) depression; (2) analyze an independent sample of depressed patients to identify any demographic and/or clinical feature that may help in differentiating mood disorder subtypes, with special attention to potential markers of bipolarity.

METHODS

A sample of 291 depressed subjects, including BP -I (n = 104), BP -II (n = 64), and unipolar (UP) subjects with (n = 53) and without (n = 70) BP family history (BPFH), was examined to evidence potential differences in clinical presentation and to validate literature-derived markers of bipolarity. Demographic and clinical variables and, also, single items from the Hamilton Depression Rating Scale (HDRS), the Montgomery-Asberg Depression Rating Scale (MADRS), and the Young Mania Rating Scale (YMRS) were compared among groups.

RESULTS

UP subjects had an older age at onset of mood symptoms. A higher number of major depressive episodes and a higher incidence of lifetime psychotic features were found in BP subjects. Items expressing depressed mood, depressive anhedonia, pessimistic thoughts, and neurovegetative symptoms of depression scored higher in UP, whereas depersonalization and paranoid symptoms' scores were higher in BP. When compared with UP, BP I had a significantly higher incidence of intradepressive hypomanic symptoms. Bipolar family history was found to be the strongest predictor of bipolarity in depression.

CONCLUSIONS

Overall, our findings confirm most of the classical signs of bipolarity in depression and support the view that some features, such as BPFH, together with some specific symptoms may help in detecting depressed subjects at higher risk for BP disorder.

Familiality and diagnostic patterns of subphenotypes in the National Institutes of Mental Health bipolar sample

Bipolar-related subphenotypes that cluster within families may help identify subsets of patients that are more genetically homogeneous. Environmental or assessment factors that segregate by family may influence estimates of familiality. We aimed to determine familiality of subphenotypes of bipolar disorder (BP), accounting for effects of age, sex, diagnosis, and site/wave of ascertainment. We studied 589 sibships with 1416 siblings affected with bipolar I (BPI), schizoaffective disorder, bipolar type (SAB), bipolar II (BPII), or recurrent unipolar depression (RUDD). Sibships were from families with > or =2 BPI cases collected by the NIMH Bipolar Genetics Initiative (NIMHBGI). Rapid cycling showed the strongest evidence for familiality [odds ratio (OR) (95%CI) = 2.02 (1.43, 2.85), P = 6.0 x 10(-5)] in a model including age, sex, diagnosis, and site/wave of ascertainment. Additional significantly familial traits were comorbid alcohol abuse/dependence (P = 2 x 10(-4)) and comorbid panic disorder (P = 8 x 10(-3)), as well as psychosis, suicidal thoughts, and rapid mood switching (P = 6 x 10(-3) - 0.03). Omission of the effect of site/wave of ascertainment from the model inflated the significance level of the apparent familial association of almost all subphenotypes from one to four orders of magnitude. We have found evidence of familiality for subphenotypes of BP. In multicenter samples, familiality may be overestimated if variability in diagnosis of subphenotypes between site/wave of ascertainment is not considered.

In search of anticipation in unipolar affective disorder

Controversial evidence exists regarding the presence of the phenomenon of anticipation in affective disorder. To further evaluate this hypothesis on the unipolar pattern of the disease, we examined 21 two-generation pairs of first and second degree relatives with unipolar recurrent major depression. Biases from index-patient and from unaffected sibs were taken into consideration. A significant difference in the age at onset and episode frequency (as measure of disease severity) between parental and offspring generation was observed. The median age at onset of the parental generation was 37+/-8.2 years compared to 22+/-8.3 years in the offspring generation (p=0.001). The offspring generation also experienced an episode frequency two times greater than the parent generation (p=0.001). Anticipation was demonstrated in 95% of pairs regarding age at onset and in 84% of pairs in episode frequency. However, the observation of a birth cohort effect may possibly explain the differences in age at onset between generations in our sample.

Investigating responders to lithium prophylaxis as a strategy for mapping susceptibility genes for bipolar disorder

Attempts to map susceptibility genes for bipolar disorder have been complicated by genetic complexity of the illness and, above all by heterogeneity. This paper reviews the genetic research of bipolar disorder aiming to reduce the heterogeneity by focusing on definite responders to long-term lithium treatment. The available evidence strongly suggests that lithium-responsive bipolar disorder is the core bipolar phenotype, characterized by a more prominent role of genetic factors. Responders to lithium have typically a family history of bipolar disorder (often responsive to lithium). They differ from responders to other mood stabilizing drugs in their family histories as well as in other clinical characteristics. The molecular genetic investigations of bipolar disorder responsive to lithium indicate possibly several loci linked to and/or associated with the illness. A combination of research strategies employing multiple methods such as linkage, association, and gene-expression studies will be needed to clarify which of these represent true susceptibility loci.

Antidepressant-induced mania: an overview of current controversies

OBJECTIVE

The prevalence, characteristics, and possible risk factors associated with antidepressant-induced mania remain poorly described. The present review sought to identify published rates of antidepressant-induced mania and describe risk factors for its emergence.

METHODS

A MedLine search was conducted of journals that focused on mania or hypomania associated with recent antidepressant use. Data from published reports were augmented with relevant findings from recent clinical trials presented at scientific conferences.

RESULTS

Antidepressant-induced manias have been reported with all major antidepressant classes in a subgroup of about 20-40% of bipolar patients. Lithium may confer better protection against this outcome when compared with other standard mood stabilizers, although switch rates have been reported with comparable frequencies on or off mood stabilizers. Evidence across studies most consistently supports an elevated risk in patients with (i) previous antidepressant-induced manias, (ii) a bipolar family history, and (iii) exposure to multiple antidepressant trials.

CONCLUSION

About one-quarter to one-third of bipolar patients may be inherently susceptible to antidepressant-induced manias. Bipolar patients with a strong genetic loading for bipolar illness whose initial illness begins in adolescence or young adulthood may be especially at risk. Further efforts are needed to better identify high-vulnerability subgroups and differentiate illness-specific from medication-specific factors in mood destabilization.

Anticipation and repeat expansion in bipolar disorder

Anticipation is the phenomenon whereby a disease becomes more severe and/or presents with earlier onset as it is transmitted down through generations of a family. The only known mechanism for true anticipation is a class of mutations containing repetitive sequences exemplified by the pathogenic trinucleotide repeat. Studies of bipolar disorder (BPD) are consistent with the presence of anticipation and, by inference, the possibility that trinucleotide repeats contribute to this disorder, although it is possible that these data are the result of methodological problems. On the assumption that anticipation in BPD may be real, several surveys of the genome of BPD probands for large trinucleotide repeats have been conducted, as have studies of many repeat-containing candidate genes. No pathogenic triplet repeat has yet been unambiguously implicated.

Triplet repeats and bipolar disorder

Anticipation, the phenomenon of a disease becoming more severe or having earlier onset as it is transmitted down the generations, was originally described in families with psychiatric illness but was thought due to ascertainment bias and became forgotten. Interest was rekindled when a number of neurodegenerative disorders that show this phenomenon, were found to be due to a novel form of mutation--unstable triplet repeats showing intergenerational expansion. Some recent studies of anticipation are consistent with its occurrence in bipolar disorder but are still associated with methodological problems making interpretation difficult. A number of case-control studies employing the repeat expansion detection (RED) technique have found longer repeats in bipolar probands but other studies have found no such association. Despite a large number of studies examining the role of various repeat containing candidate genes, a pathogenic triplet repeat has yet to be found for bipolar disorder. It is likely that the controversy surrounding anticipation and the existence of triplet repeats will only finally be resolved with the demonstration of such a mutation in the aetiology of bipolar disorder.

Studies of anticipation in bipolar affective disorder

Anticipation refers to the increase in disease severity or decrease in age of onset in successive generations. The concept evolved from the theories and dogma of degeneration that were pervasive in psychiatry and medicine in the late 19th century and into the early 20th century. The term was set aside with the criticism of geneticist Lionel Penrose, who argued that anticipation was the result of ascertainment biases. The renewed interest in anticipation followed the identification of its molecular genetic basis in the form of unstable trinucleotide repeats. Subsequently, several diseases have been studied clinically for the presence of anticipation. Although anticipation has been identified in many diseases, including bipolar disorder, only diseases showing a pattern of progressive neurodegeneration have been associated with unstable trinucleotide repeats. This review summarizes the research on anticipation in bipolar disorder and other secular trends in the patterns of the illness such as the cohort effect. The changing nature of bipolar disorder is likely to be a result of combined influences from several genes, some of which are likely to be in a state of flux, as well as environmental or cultural forces that converge to give the clinical picture of anticipation.