Month of birth as a risk factor for narcolepsy.
OBJECTIVE
A loss of hypocretin neurons has been observed in human narcolepsy; however, the cause of this disorder is still unknown. While family history and genetic factors are important individual risk factors for narcolepsy, environmental factors also contribute to the pathogenesis of the disease. The aim of the study was to find out whether there is a seasonality of month of birth in narcoleptic patients.


METHODS
Diagnosis of narcolepsy with cataplexy was based on International Classification of Sleep Disorders criteria with clinical, standard polysomnographic, and Multiple Sleep Latency Test features.


METHODS
The birth dates of 886 patients with a clear-cut diagnosis of narcolepsy with cataplexy from 3 large narcolepsy databases (352 from Montpellier-France, 157 from Montreal-Canada, and 377 from Stanford-United States of America) were compared with those of 35,160,522 subjects from the general population.


RESULTS
Patients with narcolepsy had a significantly different seasonality of month of birth compared to that of the general population. The monthly distribution of birth yielded a peak in March with a maximal odds ratio at 1.45 and a trough in September with a minimal odds ratio at 0.63. No gender or country of origin differences were observed.


CONCLUSIONS
A birth seasonality in the development of narcolepsy suggests the presence of environmental factors acting in combination with genetic factors during the fetal or perinatal period, in terms of an autoimmune process targeting the hypocretin system.
Dauvilliers
Yves
Y
Service de Neurologie B, Unité des Troubles du Sommeil, Hôpital Gui-de-Chauliac Montpellier, France. ydauvilliers@yahoo.fr
Carlander
Bertrand
B
Molinari
Nicolas
N
Desautels
Alex
A
Okun
Michele
M
Tafti
Mehdi
M
Montplaisir
Jacques
J
Mignot
Emmanuel
E
Billiard
Michel
M
D001723:Birth Rate; D001921:Brain / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D005314:Embryonic and Fetal Development; D004777:Environment; D005260:Female; D006801:Humans; D015994:Incidence; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D009290:Narcolepsy / Q000175:diagnosis* / Q000453:epidemiology / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D009479:Neuropeptides / Q000378:metabolism; D000068797:Orexins; D017286:Polysomnography / Q000379:methods; D012307:Risk Factors; D012621:Seasons
D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D000068797:Orexins