Patients with suspected narcolepsy;
patients with a history of cataplectic reactions.
HLA - DQ in Narcolepsy
Clinical Features
Narcolepsy is a sleep disorder characterized by a combination of specific clinical features.
The "narcoleptic tetrade" comprises
- daytime drowsiness (imperative sleep attacks)
- cataplexy
- sleep paralysis (muscle paralysis during the transition from sleeping to awakening) and
- hypnagogic hallucinations.
Narcolepsy can either occur as a single symptom or be polysymptomatic. For diagnostics of narcolepsy the presence of cataplexy is most important. Cataplexy is defined by a sudden bilateral muscular weakness or atonia also induced by intensive emotions such as laughter or fright. Occasionally brain tumors or anesthesia can induce cataplexy.
The underlying cause of narcolepsy yet remains to be defined. However, an association between narcolepsy and the HLA DQB1*0602 allele has been found: 90-95% of all Caucasian patients with narcolepsy carry HLA haplotype DQB1*0602. Thus, in around 5-10% of the patients this allele is absent. In the normal population this haplotype is found in around 33%. However, in some families with familial narcolepsy there was no association with the DQB1*0602 haplotype.
Cataplexy is more closely associated with the DQB1*0602 haplotype. In patients with mild or atypical narcolepsy, the DQB1*0602 haplotype is only found in 40-60%.
Genetic Information
The MHC gene cluster is located on the short arm of chromosome 6 (6p21.3); it comprises around 4Mb.
Prevalence
app. 1 : 1 000
Diagnostic
Indication
Method
HLA class II DQ typing by allele specific PCR
Sample Requirement
2 - 4 ml of EDTA blood
Duration
2 - 3 weeks