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HLA - DQ in Association with Narcolepsy

Clinical Features

Narcolepsy is a sleep disorder characterized by a combination of specific clinical features.

The "narcoleptic tetrade" is comprised of the following:

• 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 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 only around 5-10% of the patients is this allele absent. This haplotype is found in around 33% of the normal population. However, in some families with familial narcolepsy, no association with the DQB1*0602 haplotype has been found.

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 approx. 4Mb.

Prevalence

approx. 1 : 1 000

Diagnostic