Trinucleotide repeat expansions: do they contribute to bipolar disorder?

Birth-cohort and dual diagnosis effects on age-at-onset in Brazilian patients with bipolar I disorder

OBJECTIVE

Substance use disorders and birth-cohort have been associated with an earlier onset in bipolar disorder (BD). This study aimed at evaluating the inter-relations of these factors in age-at-onset in bipolar illness.

METHOD

Two-hundred and thirty patients with bipolar I disorder were cross-sectionally evaluated. Patients were categorized into four age groups for analysis. Lifetime comorbidity and age-at-onset were derived from the Structured Clinical Interview for DSM-IV.

RESULTS

There was a strong linear association between age group and age-at-onset. Lifetime alcohol and drug use disorders were also associated with age-at-onset. Illicit drug and alcohol use disorders and age group remained significant in the multivariate model. No interactions appeared.

CONCLUSION

Both age group and dual diagnoses had strong and independent impacts on age-at-onset in out-patients with BD. Substance abuse may be partly accountable for earlier symptom onset, but other features of BD in younger generations are still in need to be accounted for.

Effects of age, sex, and independent life events on amygdala and nucleus accumbens volumes in child bipolar I disorder

BACKGROUND

Relationships between environment and cortical-limbic-striatal pathways are not well-researched in child bipolar I disorder (BP-I).

METHODS

This was a controlled, blindly rated magnetic resonance imaging study of children with DSM-IV BP-I, manic or mixed type, compared with matched typically developing children (TC).

RESULTS

There were 47 subjects (21 BP-I, 26 TC) aged 14.0+/-3.1 (BP-I onset age 8.8+/-4.2). Total intracranial volume was greater in male subjects (n=28) versus female subjects (n=19) [F(1,44)=24.3, p< .001], controlling for age. Volumes were not significantly different in BP-I and TC groups, after accounting for multiple comparisons, in the medial orbital frontal cortex, rostral anterior cingulate cortex, hippocampus, amygdala (AMG), or nucleus accumbens (NAcc). Across subjects (n=47), a greater number of independent life events (ILE) was associated with smaller AMG [F(1,36)=7.8, p= .009] and NAcc [F(1,36) = 9.4, p= .004] volumes, controlling for total intracranial volume (TICV), group, age, sex, and family psychopathology. Use of stimulant medication at the time of the scan was associated with larger AMG volume [F(1,41)=9.0, p= .005], controlling for TICV, group, age, and sex. In male subjects, the age x group interaction was a significant predictor in general linear models of AMG (p= .028) and NAcc (p= .030) volumes. Effects of low maternal warmth were not significant.

CONCLUSIONS

Findings suggest that ILE affect AMG and NAcc volume, but further research is needed to examine specificity to child BP-I. Furthermore, differential age x group (child BP-I vs. TC) effects only in male subjects are consistent with differential brain development by sex.

Mania as an unique life event

Despite substantial evidence of relationship between life events and psychiatric illness in general and mood disorder in specific, none of the research has documented 'mania' itself as a life event in the onset of mania in a family member who is genetically vulnerable to the disorder. We describe three such cases that had strong temporal association between manic episode in the family member and subsequent manic episodes among the first-degree relatives. Mania as a life event might play a significant role as a precipitator towards the onset of mood disorder with a special impact on those who have vulnerability towards the disorder; the cases are discussed from both psychological and biological perspective.

Bipolar affective disorder: advances in genetics and mood-stabilising medication

The lifetime prevalence of bipolar affective disorder is between 1 % and 2%. This educational review paper focuses on two areas of interest and relevance to trainees preparing for the membership examination of the Royal College of Psychiatrists: (a) advances in the genetics of bipolar affective disorder; and (b) mood-stabilising medication in bipolar affective disorder.

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.

Characterization of CTG/CAG repeats on chromosome 18: a study of bipolar disorder

Anticipation has been frequently found in bipolar families ascertained for linkage studies. An association of polymorphic triplet repeats with the bipolar phenotype in some pedigrees has been proposed. We have previously found linkage to chromosome 18 in a set of families with evidence of anticipation. As part of a search for CAG/CTG motifs on chromosome 18, we screened a genomic chromosome 18 cosmid library and identified 65 loci with trinucleotide repeats. Eleven of 33 genotyped loci were polymorphic, though none of these showed any evidence of instability. We performed genetic analysis of six loci in the Hopkins/Dana bipolar pedigrees ascertained for a genetic linkage study of bipolar disorder and found that the CAG repeat within the AD4D2 clone on 18q21.1 showed nominally significant over-transmission of the rare CAG23 allele (P=0.034). We have characterized all 65 trinucleotide repeats and flanking sequences with GENSCAN analysis and find that 29 were predicted to be in coding regions. These 29 trinucleotide-repeat-containing genes may be involved in functional modulation of their respective proteins, and may be candidates for other diseases or disease mechanisms that map to this region.

Exclusion of non-synonymous SNPs and a polyglutamine tract in SMRT/N-CoR2 as common deleterious mutation for bipolar disorder in the Sagnenay-Lac-St-Jean population

Bipolar disorder (BP) is a psychiatric illness with both genetic and environmental components occurring with a prevalence of slightly more than 1%. Our previous linkage and case/control studies have pointed to a susceptibility locus for BP in the 12q24.31 chromosomal region. Here, we investigated the possible involvement of the SMRT/N-CoR2 gene, which encodes for the nuclear receptor co-repressor 2. SMRT/N-CoR2 was retained as a candidate gene for BP because of its location within our candidate gene region and its interactions with thyroid hormone receptors. We screened SMRT/N-CoR2 for the presence of polymorphism/mutation in coding sequences and exon-intron junctions. Four non-synonymous SNPs and a polyglutamine tract (CAG repeat) in the coding exon 14 were analyzed in a case/control sample from the Saguenay-Lac-St-Jean (SLSJ) area of Quebec (213 cases and 214 controls). Our data indicated no significant allelic/genotypic association between any of the five mutations and bipolar phenotype when they were considered either individually or as haplotypes. Finally, the CAG repeat observed in SMRT/N-CoR2 did not demonstrate allelic instability and consequently it is unlikely that this polymorphism could be involved in the anticipation phenomenon reported for BP.

Analysis of a variable number tandem repeat polymorphism in the huntingtin interacting protein-1 related gene for anticipation in bipolar affective disorder

The anticipation phenomenon, described as either an increase in disease severity, a decrease in age at onset, or both, in successive generations, has been suggested as a possibility of genetic transmission for bipolar affective disorder. We report here investigation of the stability of intergenerational transmission of a variable number tandem repeat (VNTR) polymorphism, found in the Huntingtin interacting protein-1 related gene (HIP12/HIP1R) that is mapped to the chromosome 12q24.31 region, in nine pedigrees showing decreased age at onset in successive generations. We did not observe any allelic instability but we report a deletion that includes this VNTR polymorphism. Allelic and genotypic association studies should be undertaken to verify the involvement of HIP12/HIP1R in bipolar disorder.

Chromosomal anomalies in individuals with autism: a strategy towards the identification of genes involved in autism

We review the different strategies currently used to try to identify susceptibility genes for idiopathic autism. Although identification of genes is usually straightforward in Mendelian disorders, it has proved to be much more difficult to establish in polygenic disorders like autism. Neither genome screens of affected siblings nor the large number of association studies using candidate genes have resulted in finding autism susceptibility genes. We focus on the alternative approach of 'positional cloning' through chromosomal aberrations in individuals with autism. In particular, balanced aberrations such as reciprocal translocations or inversions offer a unique opportunity, since only the genes in the breakpoint regions are candidate genes. This approach, in combination with others, is likely to produce results in the coming years.

Novel CAG/CTG repeat expansion mutations do not contribute to the genetic risk for most cases of bipolar disorder or schizophrenia

The possible presence of anticipation in bipolar affective disorder and schizophrenia has led to the hypothesis that repeat expansion mutations could contribute to the genetic etiology of these diseases. Using the repeat expansion detection (RED) assay, we have systematically examined genomic DNA from 100 unrelated probands with schizophrenia and 68 unrelated probands with bipolar affective disorder for the presence of CAG/CTG repeat expansions. Our results show that 28% of the probands with schizophrenia and 30% of probands with bipolar disorder have a CAG/CTG repeat in the expanded range, but that each expansion could be explained by one of three nonpathogenic repeat expansions known to exist in the general population. We conclude that novel CAG/CTG repeat expansions are not a common genetic risk factor for bipolar disorder or schizophrenia.

Studies of offspring of parents with bipolar disorder

Children and adolescents who are the biological offspring of individuals with bipolar disorder (BD) (bipolar offspring) represent a population rich in potential for revealing important aspects in the development of BD. Multiple cross-sectional assessments of psychopathology in bipolar offspring have confirmed high incidences of BD, as well as mood and behavioral disorders, and other psychopathology in this population. Longitudinal studies of offspring have begun to shed light on precursors of BD development. Other assessments of bipolar offspring have included dimensional reports of psychiatric and psychosocial functioning, temperament assessments, and descriptions of family environments and parenting styles. Neurobiological studies in bipolar offspring are just beginning to yield findings that may be related to the underlying neuropathophysiology of BD. The future holds promise for longitudinal studies of bipolar offspring incorporating all of these facets, including genetic analyses, to further elucidate the factors involved in the evolution of BD.

Bipolar offspring: a window into bipolar disorder evolution

Children of parents with bipolar disorder (bipolar offspring) represent a rich cohort for study with potential for illumination of prodromal forms of bipolar disorder. Due to their high-risk nature, bipolar offspring may present phenomenological, temperamental, and biological clues to early presentations of bipolar disorder. This article reviews the evidence for establishing bipolar offspring as a high-risk cohort, the studies which point to possible prodromal states in bipolar offspring, biological findings in bipolar offspring which may be indicators of even higher risk for bipolar disorder, initial attempts at early intervention in prodromal pediatric bipolar disorder, and implications for future research.

A novel CpG-associated brain-expressed candidate gene for chromosome 18q-linked bipolar disorder

We previously identified 18q21-q22 as a candidate region for bipolar (BP) disorder and constructed a yeast artificial chromosome (YAC) contig map. Here we identified three potential CpG islands using CCG/CGG YAC fragmentation. Analysis of available genomic sequences using bioinformatic tools identified an exon of 3639 bp downstream of a CpG island of 1.2 kb containing a putative transcription initiation site. The exon contained an open reading frame coding for 1212 amino acids with significant homology to the SART-2 protein; weaker homology was found with a series of sulphotransferases. Alignment of cDNA sequences of corresponding ESTs and RT-PCR sequencing predicted a transcript of 9.5 kb which was confirmed by Northern blot analysis. The transcript was expressed in different brain areas as well as in multiple other peripheral tissues. We performed an extensive mutation analysis in 113 BP patients. A total of nine single nucleotide polymorphisms (SNPs) were identified. Five SNPs predicted an amino acid change, of which two were present in BP patients but not in 163 control individuals.