Many poor sleepers are convinced that sleep disturbances ‘run in the family’, often mentioning, for example, that their mother, father, brother or sister also experience difficulties with sleep. Research studies do support this possibility, but well-controlled, thorough investigations are lacking. In a recent study, published in Sleep Medicine, researchers from The Chinese University of Hong Kong assessed whether close relatives of those with insomnia were more likely to also experience insomnia compared to the relatives of normal sleepers.
The research team recruited 75 adolescents with insomnia (plus 180 of their first-degree relatives) and compared them with 141 normal sleeping adolescents without insomnia (and 382 of their first degree relatives). A major strength of the study was that all participants (including relatives) received a thorough clinical interview to help characterise insomnia as well as the presence of any additional psychiatric disorders.
The main findings were that parents of adolescents with insomnia had higher rates (more than two-fold) of experiencing both current and lifetime history of insomnia relative to the parents of normal sleepers. This increased risk was more likely to be present in mothers than fathers. Importantly, familial aggregation of insomnia remained even after controlling for additional psychiatric disorders; that is, insomnia appears to have high heritability even after accounting for additional psychiatric illness.
The authors suggest that high rates of heritability may be related to the fact that adolescents were recruited in the present study, and that early-onset insomnia may be more heritable than adulthood-onset insomnia. They also suggest that greater maternal (mother) influence of insomnia may be explained by more direct genetic transmission and environmental factors (e.g. closer contact leading to greater influence on lifestyle practices). A limitation of the study was that other sleep disorders (like restless legs syndrome and delayed sleep phase syndrome) were not assessed. These disorders are commonly associated with insomnia and may potentially impact the results.
The authors conclude “Our study demonstrates a significant familial aggregation and a high heritability of insomnia even upon the exclusion of comorbid psychiatric disorders, which argue for the genetic basis of insomnia and family-based intervention for insomnia. Further molecular genetic study of insomnia is indicated.”
Wing, Y., Zhang, J., Lam, S., Li, S., Tang, N., Lai, K., Li, A. (2012). Familial aggregation and heritability of insomnia in a community-based study. Sleep Medicine, 13 (8), 985-990.