Association Study of HLA-DQB1*0602 Allele in Iranian Patients with Narcolepsy

Abstract

Narcolepsy is a rare, disabling disorder characterized by excessive daytime sleepiness, cataplexy, hypnagogic hallucinations and sleep paralysis. Several studies demonstrated its association with HLA-DQB1*0602 in various ethnic groups. Our study aimed to determine the prevalence of HLA-DQB1*0602 allele in Iranian patients with narcolepsy and assess its predictive parameters for diagnosing narcolepsy. In addition, car accidents and job problems were assessed among narcoleptic patients. We studied 44 narcoleptic patients, 30 patients with other types of excessive daytime sleepiness (EDS)  and 50 healthy age and sex matched individuals in this case-control study. Patients and controls filled out a questionnaire including items about car accidents due to sleepiness and job problems. International classification of sleep disorders-2 criteria was used as the gold standard for diagnosis of narcolepsy. The DNAs isolated from whole blood samples were collected from the patients and controls to assess the presence of HLA-DQB1*0602. The results showed that HLA DQB1*0602 was present in 4 (8%) individual of controls and 20 (45.5%) patients with higher prevalence in patients with cataplexy (78.9%) than patients without cataplexy (p<0.001). The sensitivities of the DQB1*0602 for diagnosing narcolepsy with cataplexy and narcolepsy without cataplexy were 78.9 and 20; specificities were 88 and 72.4, respectively. 18.2% of patients had car accidents due to sleepiness and 68.2% suffered from job problems. Our study shows that evaluation of DQB1*0602 in patients suspected to narcolepsy could be helpful especially in complex cases with atypical cataplexy and indistinguishable multiple sleep latency test MSLT results. Moreover, high rates of car accidents and job problems are found among narcoleptic patients.