Heritability of cognitive functions in families with bipolar disorder

Abstract

Bipolar disorder is highly heritable. Cognitive dysfunctions often observed in bipolar patients and their unaffected relatives implicate that these impairments may be associated with genetic predisposition to bipolar disorder and thus fulfill the criteria of a valid endophenotype for the disorder. However, the most fundamental criterion, their heritability, has not been directly studied in any bipolar population. This population-based study estimated the heritability of cognitive functions in bipolar disorder. A comprehensive neuropsychological test battery and the Structured Clinical Interview for DSM-IV were administered to a population-based sample of 110 individuals from 52 families with bipolar disorder. Heritability of cognitive functions as assessed with neuropsychological test scores were estimated using the Solar package. Significant additive heritabilities were found in verbal ability, executive functioning, and psychomotor processing speed. Genetic contribution was low to verbal learning functions. High heritability, in executive functioning and psychomotor processing speed suggest that these may be valid endophenotypic traits for genetic studies of bipolar disorder.

Neurological soft signs and cognitive functions: Amongst euthymic bipolar I disorder cases, non-affected first degree relatives and healthy controls

“…However, literature so far has been inconsistent on the type of cognitive tasks that are impaired in relatives, with some studies revealing deficits in executive functioning as well as response-inhibition (Antila et al, 2007; Zalla et al, 2004), while other studies suggest a deficit in response inhibition only (Frangou et al, 2005). A meta-analysis for 18 cognitive variables between relatives, patients and healthy controls reported mixed results (Bora et al, 2009).…”

Cognitive Impairment in Bipolar Disorder

“…Furthermore, they should be state-independent traits present in illness as well as in remission, and they should be more frequent in unaffected relatives of patients than in general population 4 . The endophenotype criterion of heritability has been met for certain neurocognitive functions in a study of a population-based Finnish sample of 110 individuals from 52 families with bipolar disorder who were administered a comprehensive test battery 51 . The results indicated high heritability of executive functions and psychomotor processing speed, but not of verbal learning.…”

The Effect of Processing Speed on Cognitive Functioning in Patients with Familial Bipolar I Disorder and Their Unaffected Relatives

“…The role of slowed processing speed in verbal memory has been evidenced in other mental disorders including schizophrenia [9][10][11] and depression [12] and also in a twin sample of bipolar I disorder patients [13] . According to our previous studies of bipolar I disorder patients and their first-degree relatives, processing speed may be a potential endophenotype [14] for bipolar disorder [4,15] . In our previous study, we found that both the patients with familial bipolar I disorder and their unaffected first-degree relatives were significantly impaired compared to the controls in the task measuring processing speed (assessed with the digit symbol subtest of the Wechsler Adult Intelligence Scale-Revised, WAIS-R) [4] .…”