The genetics of pediatric-onset bipolar disorder

Absence of gender differences in pediatric bipolar disorder: findings from a large sample of referred youth

BACKGROUND

Because little is known about gender differences in pediatric bipolar disorder, we evaluated whether gender moderates the expression of pediatric bipolar disorder in a large clinical sample.

METHODS

Subjects were consecutively referred youth aged 18 years or less who met full criteria for DSM-III-R bipolar disorder (BPD) (females, n=74; BD males, n=224). All subjects were assessed with a structured diagnostic interview and measures of psychosocial and family functioning.

RESULTS

Most of the bipolar subjects (91% of males, 70% of females) also had ADHD. Bipolar disorder was equally prevalent in both genders. Among females and males, severe irritability (83% and 80%, respectively), mixed presentation (87% and 84%, respectively), chronic course (84% and 77%, respectively) and prepubertal onset (78% and 93%, respectively) predominated the clinical picture. We found no meaningful differences between genders in the number of BPD symptoms, type of treatment for BPD (counseling, medication, hospitalization), severity of educational deficits, severity of family and interpersonal functioning or patterns of psychiatric comorbidity.

CONCLUSIONS

Because gender does not moderate the clinical expression of pediatric bipolar disorder, our data does not suggest that gender specific criteria for the disorder are warranted.

A genome-wide scan of symptom dimensions in bipolar disorder pedigrees of adult probands

Although twin and adoption show bipolar disorder (BP) has a strong genetic component, few chromosomal regions have been consistently implicated by molecular genetic studies. To address this issue, we sought to determine if quantitative dimensions of bipolar disorder symptoms would be useful for detecting genes that underlie the susceptibility to bipolar disorder. Subjects were 520 individuals diagnosed with bipolar I, bipolar II or schizoaffective disorder, bipolar type who had participated in the NIMH genetics initiative for bipolar disorder. We constructed symptom scores from 29 psychiatric symptoms recorded in the Diagnostic Interview for Genetic Studies (DIGS). Principal components factor analysis followed by a varimax rotation was used to extract symptom dimensions. Factor scores were calculated for all genotyped individuals in the sample, regardless of affection status. Heritable factors were used in a variance-components linkage analysis, which utilized the exact likelihoods of allele-sharing identical-by-descent for each pair of relatives within each pedigree. The principal components factor analysis resulted in five independent dimensions: depressed state, psychosis, sleep disturbances, psychomotor acceleration, and irritability. Two factors were significantly heritable: depression (h2=0.53, p<0.001) and irritable vs. euphoric mania (h2=0.35, p=0.03). These were subsequently used in a linkage analysis that resulted in LOD scores of <2.0, which are not statistically significant. The five constructs developed through factor analysis appear to be consistent with previous factor analyses. Notably, only the dimensions associated with the type of mood disturbance showed high heritability, which suggests that careful measurements of depression, euphoria and irritability may be particularly useful in clarifying the genetic etiology of bipolar disorder in future studies.

Molecular genetics of affective disorders

Evidence for familial aggregation in Affective Disorders (AD) has been provided in classical studies. Linkage and association genetic studies have been proposed to detect genetic factors implicated in AD. However, findings from molecular genetic studies remain inconclusive. Nevertheless, current research is focusing on the phenotypes, both sub- and endophenotypes. In addition, recent advances in technology, such as microarrays, provide new tools in psychiatric genetics. These different approaches offer a new optimism era in the search of genetic factors in AD.