Vulnerability to insomnia: the role of familial aggregation

The goal of this study was to determine the degree of familial aggregation in vulnerability to stress-related sleep disturbance among siblings. One approach to investigating a potential "familial" predisposition to sleep disturbance is to examine the relationship between siblings on a standard measure of vulnerability to stress-related sleep disturbance.

Cross-sectional data on insomnia, vulnerability to stress-related sleep disturbance, sleepiness, habitual sleep, and additional demographic variables was collected separately from pairs of biological siblings. Data were collected during a 15-20min phone assessment.

Interviews on a total of 62 individuals (31 sibling pairs) were completed. A total of 8 individuals and their respective siblings were excluded after meeting conservative criteria for Diagnostic and Statistical Manual of Mental Disorders, Fourth edition (DSM-IV)-based insomnia. The mean age of the sample was 51.1+/-12.1 years (range 18-70) and habitual nightly total sleep time averaged 6.91+/-1.42h/night.

Individuals completed the Ford Insomnia Response to Stress Test (FIRST), a standardized measure of individual vulnerability to stress-induced sleep disturbance. The intraclass correlation coefficient (ICC) was r =0.61, df=23, p =0.001 for the relationship between siblings in FIRST scores. This indicated that 37.2% of the variance in vulnerability to stress-related sleep disturbance can be accounted for by familial aggregation. This relationship remained after controlling for potential confounds including age, gender, shift schedule, and psychiatric history.

Our data support the notion that vulnerability to stress-related sleep disturbance has a strong familial aggregation. Additional studies are needed to determine the genetic or environmental origins of this relationship and its underlying biological substrates.