NARCOLEPSY-LIKE SYMPTOMS AMONG ADULT TWINS

The genetic architecture of narcolepsy is poorly known. Genetic and en vironmental components of symptoms characteristic of narcolepsy, exces sive sleepiness and cataplexy were assessed in a population-based samp le of middle-aged like-sexed twin pairs. Questionnaire assessment of t he 11-item Ullanlinna Narcolepsy Scale (UNS), a validated screening in strument for narcolepsy [J. Sleep Res. (1994) 3, 52-59] and two subsca les (sleepiness and cataplexy-like symptoms) was obtained from both tw ins of 3785 pairs aged 33-60 y (541 male MZ pairs, 1089 male DZ pairs, 781 female MZ and 1374 female DZ pairs) from the population-based Fin nish Twin Cohort. For the UNS scores, the intraclass correlation for m ale MZ pairs was 0.365 and for male DZ pairs 0.072, while for female p airs the MZ correlation was 0.375 and for DZ pairs 0.155. Structural e quation model fitting indicated that a model with additive and non-add itive genetic effects, and idiosyncratic environmental effects best ac counted for the pattern of twin resemblance in both men and women. Gen etic effects accounted for 35% (in men) and for 39% (in women) of tota l phenotypic variance in UNS. Analysis of the subscales suggested that there may be a greater genetic component to the sleepiness subscale, while environmental components play more of a role in the development of cataplexy-like symptoms. Further investigation of the complex genet ic architecture of narcolepsy and its symptoms is warranted.