Is processing speed a valid cognitive endophenotype for bipolar disorder?

Area of Science:

• Neuroscience
• Psychiatry
• Cognitive Psychology

Background:

• Bipolar disorder (BD) diagnosis relies on clinical symptoms, but endophenotypes can aid early detection.
• Processing speed is a cognitive function frequently affected in various psychiatric conditions.

Purpose of the Study:

• To determine if processing speed, assessed via the Digit Symbol Test (DST), serves as a valid endophenotype for bipolar disorder (BD).
• To evaluate the utility of DST in differentiating individuals with BD and their relatives from healthy controls.

Main Methods:

• The study involved 53 euthymic BD probands (BD-P), 50 unaffected first-degree relatives (UFDR), and 60 healthy controls (HC).
• Processing speed was measured using the Digit Symbol Test (DST).
• Statistical analyses controlled for demographic factors and current mood symptoms.

Main Results:

• Euthymic BD-P and UFDR groups showed significantly poorer performance on the DST compared to HC (effect sizes 0.89 and 0.52, respectively).
• Approximately 30% of BD-P and 25% of UFDR exhibited clinically significant performance impairment.
• The DST demonstrated high specificity in differentiating BD-P and UFDR from HC.

Conclusions:

• Processing speed, as measured by the DST, is a reliable and brief cognitive assessment.
• Findings support processing speed as a valid endophenotype for bipolar disorder.
• The DST can be valuable in clinical assessments of at-risk populations for BD.