Longitudinal study of narcolepsy symptoms in first, second, and third-degree relatives of simplex and multiplex narcolepsy families

Abstract Objective To assess the evolution of narcolepsy symptoms in first-, second, and third-degree relatives and to compare multiplex and simplex families. Methods A total of 4045 family members and 362 narcoleptic individuals were entered in the study; with 3255 family members interviewed twice, five to seven years apart. A control group (n = 178) composed of spouses or housemates was also interviewed twice. Family members were divided according to their blood relationship with the probands and further divided into multiplex (ie, more than one narcolepsy cases) and simplex (only one narcolepsy case) families. Telephone interviews were conducted with the help of the Sleep-EVAL system; narcolepsy probands were evaluated and diagnosed by a Sleep Specialist in a Sleep Clinic Center. Results A total of 1123 family members from 72 families were identified as members of multiplex families while the rest of the sample were a part of simplex families (n = 2132). Multiplex families had higher incidence and chronicity of hypersomnolence than the simplex family members and the control group. For cataplexy-like symptoms, only prevalence at the time of the first assessment distinguished multiplex (5.5%) and simplex (2.9%) families. Prevalence of sleep paralysis was higher among the first- and second-degree relatives coming from multiplex families, while incidence was the highest among second- and third-degree relatives. Hypnagogic hallucinations had similar prevalence between multiplex and simplex families but the incidence and chronicity were significantly higher among multiplex families. For each symptom, predictive factors were also determined in simplex and multiplex families. Conclusions Our results show that individuals coming from multiplex families are at greater risks of a broad range of narcolepsy symptoms compared to simplex families.