A linkage and family-based association analysis of a potential neurocognitive endophenotype of bipolar disorder

Monoamine oxidase a gene polymorphisms and bipolar disorder in Iranian population

BACKGROUND

Bipolar disorder (BPD) is a common and severe mood disorder. Although genetic factors have important rolesin the etiology of bipolar disorder, no specific gene has been identified in relation to this disorder. Monoamine oxidase gene is suggested to be associated with bipolar disorder in many studies.

OBJECTIVES

This study aimed to investigatethe role of MAOA gene polymorphisms in the etiology of bipolar disorder in Iranian population.

PATIENTS AND METHODS

This study is a case-control study, with convenient sampling. Three common polymorphisms, a CA microsatellite, a VNTR, and a RFLP were typed in 156 bipolar patients and 173 healthy controls. Patients were chosen from Imam Hossein General Hospital, Psychiatry Ward (Tehran/Iran). Controlsamples for this study consisted of 173 healthy individuals recruitedby convenient sampling. Allelic distributions of these polymorphisms were analyzed in bipolar and control groups to investigate any association with MAOA gene.

RESULTS

Significant associations were observed regarding MAOA-CA (P = 0.016) and MAOA-VNTR (P = 0.004) polymorphisms in the bipolar females. There was no association between MAOA-RFLP and bipolar disorder.

CONCLUSIONS

The obtained results confirm some previous studies regardinga gender specific association of MAOA gene with the bipolar disorder.

DRD4 VNTR polymorphism and age at onset of severe mental illnesses

A large number of studies has investigated the hypothesis that DRD4 48 bp variable number of tandem repeat (VNTR) polymorphism is involved in the etiology of schizophrenia and bipolar disorder. However, the results are inconsistent likely due to genetic and phenotypic heterogeneity. Age at onset (AAO) is considered an important alternate phenotype for genetic investigations of psychiatric disorders. In the present study, the DRD4 VNTR 7 repeat allele (7R) was examined in 477 patients with major psychoses. Age at onset was defined as the age of first psychotic episode for schizophrenia and the age at appearance of first clinically recognized symptoms for the bipolar sample. Our results showed an interaction between sex and DRD4 genotypes among schizophrenia patients (n=203, β=.213, p=.017). On comparing AAO between carriers and non-carriers of the 7R, we observed that females with 7R present had later onset (p=.021). The effect was not observed for males. In the sample with bipolar disorder, we observed significant association between DRD4 7R-genotype and AAO (n=274, β=-.148, p=.012). No interaction was observed between sex and genotypic groups of the bipolar sample. The 7R was associated with early onset of the bipolar illness (p=.028). In summary, our results suggest that the 7R is associated with AAO in both schizophrenia and bipolar disorders. The effect was observed across both sexes in bipolar disorder, but specifically in females for schizophrenia.

Differential association between MAOA, ADHD and neuropsychological functioning in boys and girls

Attention-deficit/hyperactivity disorder (ADHD) is more common in boys than in girls. It has been hypothesized that this sex difference might be related to genes on the X-chromosome, like Monoamine Oxidase A (MAOA). Almost all studies on the role of MAOA in ADHD have focused predominantly on boys, making it unknown whether MAOA also has an effect on ADHD in girls, and few studies have investigated the relationship between MAOA and neuropsychological functioning, yet this may provide insight into the pathways leading from genotype to phenotype. The current study set out to examine the relationship between MAOA, ADHD, and neuropsychological functioning in both boys (265 boys with ADHD and 89 male non-affected siblings) and girls (85 girls with ADHD and 106 female non-affected siblings). A haplotype was used based on three single nucleotide polymorphisms (SNPs) (rs12843268, rs3027400, and rs1137070). Two haplotypes (GGC and ATT) captured 97% of the genetic variance in the investigated MAOA SNPs. The ATT haplotype was more common in non-affected siblings (P = 0.025), conferring a protective effect for ADHD in both boys and girls. The target and direction of the MAOA effect on neuropsychological functioning was different in boys and girls: The ATT haplotype was associated with poorer motor control in boys (P = 0.002), but with better visuo-spatial working memory in girls (P = 0.01). These findings suggest that the genetic and neuropsychological mechanisms underlying ADHD may be different in boys and girls and underline the importance of taking into account sex effects when studying ADHD.

Neuropsychological task performance in bipolar spectrum illness: genetics, alcohol abuse, medication and childhood trauma

INTRODUCTION

Impaired executive and memory function is a putative genetic trait marker of bipolar I disorder (BPD I). Although executive/memory function has been posited to be an endophenotype of BPD I, it is unclear whether this extends to bipolar spectrum illness. It is also unclear to what extent non-genetic factors such as childhood abuse, alcoholism and medication influence neurocognitive function. We assessed the neuropsychological performance of a large cohort of bipolar disorder probands and their affectively ill and healthy family members, while controlling for self-reported childhood sexual and emotional abuse, emotional neglect, alcohol abuse and medication.

METHODS

A total of 230 largely euthymic participants from 47 families, comprising 49 subjects with BPD I, 19 with bipolar II disorder (BPD II), 44 with recurrent major depression (MDE-R), 33 with a single lifetime episode of depression (MDE-S), 20 with other DSM-IV diagnoses and 65 unaffected relatives, were assessed with a battery of neuropsychological tasks.

RESULTS

Sexual abuse, emotional abuse and emotional neglect scores were associated with poorer cognitive performance. After controlling for childhood trauma, the BPD I group performed worse than unaffected relatives on tests of visual recall memory as well as verbal recall and recognition memory. In contrast, individuals with BPD II and bipolar spectrum illness did not differ significantly from unaffected relatives. Treatment with lithium and antipsychotic medication was associated with reduced executive and verbal recognition memory function. After controlling for medication and other covariates, only verbal recall memory was significantly impaired in the BPD I cohort.

CONCLUSIONS

Verbal recall deficits may be one manifestation of a genetically driven dysfunction of frontal-striatal cortical networks in BPD I.