Clinical features of narcolepsy usually begin in the teens or twenties, although diagnosis may be established years later. Onset after 50 years of age is unusual. The classic symptoms of narcolepsy are:
- excessive daytime sleepiness – feeling very drowsy throughout the day, and having difficulty concentrating and staying awake;
- cataplexy – temporary loss of muscle control resulting in weakness and possible collapse, often in response to emotions such as laughter and anger;
- hallucinations upon falling asleep (hypnagogic hallucinations) and/or upon awakening (hypnopompic hallucinations);
- sleep paralysis – a generalized temporary inability to move or speak when waking up or falling asleep;
- sleep attacks – falling asleep suddenly and without warning
Many people with narcolepsy do not know they have the sleep disorder. In general, narcolepsy affects 1 in 3,000 individuals 2). The overall prevalence of narcolepsy in the general population of the United States and Europe is about 0.05 percent 3). The prevalence varies worldwide from less than 0.02 percent of the population in Israel, to about 0.15 percent of the population in Japan 4). Narcolepsy may run in some families, but most cases are not genetic. The disorder is extremely rare in children. The cause of narcolepsy is still unknown, but recent research suggests that many people with narcolepsy with cataplexy have low levels of the neurotransmitter hypocretin, a chemical that regulates arousal, wakefulness and appetite.
Specific genetic factors are thought to contribute to narcolepsy. First-degree relatives of narcoleptic patients have a 20-40-fold increased risk of experiencing narcolepsy with cataplexy, indicating that it has a genetic component 5).
A number of studies have shown that narcolepsy has a negative social, psychological, economic, educational, and vocational effect on people with the condition, and a negative socioeconomic impact on their partner 6). As there is no known cure, current treatments for narcolepsy aim to improve symptoms 7).
Although the specific mechanisms of narcolepsy are not fully understood, recent studies demonstrate that narcolepsy with cataplexy is secondary to the loss of hypocretin neurons in the hypothalamus and is associated with human HLA DQB1*0602, and could be autoimmune 8). The prevalence of narcolepsy with cataplexy ranges between 25 and 50 per 100,000 people worldwide 9).
Narcolepsy affects both genders and typically begins between age 15 and 24, although it has been found in children as young as 5 years old. The age at onset varies from early childhood to mid-adulthood and has a bimodal distribution with an early peak of the disease at 14.7 years and a late peak at 35 years 10). Narcolepsy rarely develops after age 40.
According to the International Sleep Disorder Classification-3rd edition, narcolepsy can be divided into two groups: