Narcolepsy Genotyping (HLA-DQB1*06:02)
Label Mnemonic: NARC
Epic Lab Code: LAB7502
Downtime Form: A-1a Miscellaneous Request
Commercial Mail-out Laboratory
5231 RCP
356-8593
Specimen(s):
Whole Blood
Collection Medium:
Lavender top tube 3 mL (EDTA)
Minimum:
Preferred Minimum: 3 mL whole blood from lavender top tube
Absolute Minimum: 1 mL whole blood from lavender top tube
Testing Schedule:
Time Varies
Turn Around Time:
10 days upon receipt at reference laboratory
Reference Range:
By Report
Interpretive Data:
Background Information for Narcolepsy (HLA-DQB1*06:02) Genotyping:

Characteristics: Narcolepsy is a sleep disorder associated with invalidating excessive daytime sleepiness and cataplexy (the sudden loss of muscle tone triggered by strong emotions). Additionally, disturbed nighttime sleep, sleep paralysis, and hypnagogic hallucinations (occurring in the period between sleep and wakefulness) are common.

Incidence: Narcolepsy affects approximately 1 in 2,000 individuals.

Cause: The HLA-DQB1*06:02 allele is strongly associated with narcolepsy, but, by itself, is not causative. Recent studies indicate HLA-DRB1*15 is no longer associated with narcolepsy.

Mutations Tested: HLA-DQB1*06:02 allele.

Clinical Sensitivity: 85-95 percent depending on ethnicity. Greater than 99 percent of affected Caucasians with cataplexy have the HLA-DQB1*06:02 allele.

Clinical Specificity: Less than 1 percent; 15-25 percent of unaffected Caucasians have the HLA-DQB1*06:02 allele.

Analytical Sensitivity and Specificity: 99 percent.
Test Limitations:
This methodology will not differentiate between individuals who are heterozygous (one copy) and those who are homozygous (two copies) for the HLA-DQB1*06:02 allele. Rare diagnostic errors may occur due to primer site mutations. Alleles other than HLA-DQB106:02 will not be identified. Other genetic and non genetic factors that influence narcolepsy are not evaluated.
Methodology:
Polymerase Chain Reaction/Fluorescence Monitoring
CPT Code:
81383