Insomnia has many causes, and we shouldn’t forget some people have a great natural tendency to insomnia.
There is evidence of a genetic predisposition to insomnia, although larger studies are required to say how much inheritance plays in DIMS (a formal name for Difficulty in Instituting and Maintaining Sleep). Family history should not be surprising as a factor given that other factors correlated with insomnia include an uptight nervous disposition, a particular metabolism and body type, and a tendency to hyperarousal, which all have a genetic component.
A survey has shown people with a family history of insomnia tend to score higher on formal measures of predisposition to arousal and symptoms of anxiety. People with a history of insomnia reported family sleep problems at a greater rate than those who never had insomnia.
Study of siblings supports the hypothesis of a genetic component. As measured by the Ford Insomnia Response to Stress Test (FIRST) siblings have correlated tendencies to insomnia. Because siblings tend to be raised together, it could be argued that there is an environmental component in this finding.
Canadian researchers looking at the incidence of new cases of sleep onset insomnia in a large population identified 5 risk factors:
Note that this is primary insomnia (no obvious cause) and sleep onset insomnia (the kind more common in young adults in contrast to older adults who tend to sleep maintenance insomnia.) The family history and the predisposition to arousability are at least partly genetic.
Another large study found people with insomnia were more likely to have a first-degree relative with insomnia (46%) than good sleepers were (33%). Other studies have looked at how common stress-related insomnia in pairs of siblings. The conclusion was that a predisposition to stress-related insomni when a first-degree relative had that kind of insomnia. It also showed that people without this kind of insomnia were more likely to have relatives without it. By showing both sides of the question to some degree of confidence, the researchers showed evidence of an inherited susceptibility to insomnia
An extremely rare and dangerous sleep disorder is fatal familial insomnia. This is a prion disease and as the name implies genetic. The subject usually develops severe insomnia in their 30s and progresses to brain degradation and death.