Identification of the variations in the CPT1B and CHKB genes along with the HLA-DQB1*06:02 allele in Turkish narcolepsy patients and healthy persons

Abstract

Background: The HLA-DQB1*06:02 allele across all ethnic groups and the rs5770917 variation between CPT1B and CHKB genes in Japanese and Koreans are common genetic susceptibility factors for narcolepsy. This comprehensive genetic study sought to assess variations in CHKB and CPT1B susceptibility genes and HLA-DQB1*06:02 allele status in Turkish patients with narcolepsy and healthy persons.

Methods: CHKB/CPT1B genes were sequenced in patients with narcolepsy (n=37) and healthy persons (n=100) to detect variations. The HLA-DQB1*06:02 allele status was determined by sequence specific polymerase chain reaction.

Results: The HLA-DQB1*06:02 allele was significantly more frequent in narcoleptic patients than in healthy persons (p=2×10(-7)) and in patients with narcolepsy and cataplexy than in those without (p=0.018). The mean of the multiple sleep latency test, sleep-onset rapid eye movement periods, and frequency of sleep paralysis significantly differed in the HLA-DQB1*06:02-positive patients. rs5770917, rs5770911, rs2269381, and rs2269382 were detected together as a haplotype in three patients and 11 healthy persons. In addition to this haplotype, the indel variation (rs144647670) was detected in the 5' upstream region of the human CHKB gene in the patients and healthy persons carrying four variants together.

Conclusion: This study identified a novel haplotype consisting of the indel variation, which had not been detected in previous studies in Japanese and Korean populations, and observed four single-nucleotide polymorphisms in CHKB/CPT1B. The study confirmed the association of the HLA-DQB1*06:02 allele with narcolepsy and cataplexy susceptibility. The findings suggest that the presence of HLA-DQB1*06:02 may be a predictor of cataplexy in narcoleptic patients and could therefore be used as an additional diagnostic marker alongside hypocretin.

FIG. 1.

Agarose gel electrophoresis showing the presence or absence of HLA-DQB1*06:02 allele. Lanes 2, 3, 4, and 5 represent HLA-DQB1 *06:02 allele positivity and lane 1 represents HLA-DQB1*06:02 allele negativity. M: 100–base pair DNA ladder. ^aInternal control of polymerase chain reaction. HGH1, human growth hormone 1.

FIG. 2.

rs144647670 deletion sequence. (A) Multiple sequence alignment of the region including the deletion (black box) in 5′ upstream of the human CHKB across 21 species. The figure is generated using GRCh37/hg19 [The European Bioinformatics Institute (EMBL-EBI)], a ClustalW method, and Jalview Java alignment editor version 2. (B) The sequence electropherogram of patients carrying the wild type (B1), homozygote (B2), and the heterozygote (B3) deletion region. (C) The genomic localization of the regulatory region of the CHKB gene and track illustration of 20–base pair deletion (rs144647670) according to GRCh37/hg19 (University of California Santa Cruz).