Population-based studies of KLS have not been performed. Its prevalence is about 1 case per million people. In France, KLS has a prevalence of 1.5 per million people. It occurs most frequently among Jews in the US and Israel. First-degree relatives of people who have suffered from the syndrome are much more likely than the general population to suffer from it, although only in about one percent of cases do family members contract it. About 70 to 90 percent of patients are male. Patients with the syndrome are more likely than the general population to have genetic disorders, and about a third of people with the syndrome encountered some form of birth difficulty. In a study of 186 older patients, about ten percent had preexisting psychiatric issues. One study found that about ten percent of patients had a neurological condition before KLS developed. The condition does not appear to occur most frequently in one season.
Kleine–Levin syndrome
Bulimia nervosa
Temple–Baraitser syndrome
Adams–Nance syndrome
Frey's syndrome
Urban–Rogers–Meyer syndrome
Wallis–Zieff–Goldblatt syndrome
Nance–Horan syndrome