Final intra-assay CV was 0.0% to 9.4% and inter-assay CV was 1.3% to 8.8%. 10?4) or controls (4.5% of 156, OR = 7.1, 95% CI = 3.1 – KC01 16.2, P = 9.3 10?6). Anti-TRIB2 positivity in controls was not associated with narcolepsy-cataplexy cases, the presence of anti-TRIB2 was associated with short disease duration (2.3 years from cataplexy onset), with 41.0% positive in this group (OR = 7.4 versus cases with onset 2.3 years, 95% CI = 1.9 – 28.5, P = 9.0 10?4). Anti-TRIB2 positivity in 39 positive recent onset cases was associated with increased ASO antibody ( 200 IU) (OR = 6.2, 95% CI = 1.6 – 24.6, P = 0.01), but did not correlate with age, gender, or body mass index. Conclusion: Anti-TRIB2 autoantibodies are strongly associated with narcolepsy close to cataplexy onset ( 2.3 years). Anti-TRIB2 was rarely found in cases without cataplexy or with distant onset. Citation: Kawashima M; Lin L; Tanaka S; Jennum P; Knudsen S; Nevsimalova S; Plazzi G; Mignot E. Anti-Tribbles homolog 2 (TRIB2) autoantibodies in narcolepsy are associated with recent onset of cataplexy. 2010;33(7):869-874. allele.1 In most human narcolepsy cases with cataplexy, hypocretin-1 concentration is reduced or undetectable in the cerebrospinal fluid (CSF).2,3 The lack of CSF hypocretin (HCRT) is due to a 90% to 95% loss of HCRT neurons in postmortem brains of narcolepsy patients, without apparent alteration of adjacent neurons, such as those expressing melanin-concentrating hormone.4 As a lack of HCRT or HCRT receptors causes narcolepsy in animal models,5,6 the loss of HCRT transmission is the likely cause of the symptoms in human narcolepsy. Even though tight HLA association suggests a potential autoimmune destruction of HCRT neurons as the etiology of most narcolepsy cases, the proof for such a mechanism has remained elusive.7 A recent genome-wide association study found a strong additional association between narcolepsy and polymorphisms in T cell receptor alpha gene (positivity were considered to have HCRT deficiency, based on prior data indicating a higher than 90% correspondence.15 We also included a small number of extremely rare atypical cases that were negative with low CSF hypocretin-1 ( 110 pg/mL) (n = 4), DQB1*0602 positive with normal CSF hypocretin-1 ( 200 pg/mL) (n = 3), and negative with normal CSF hypocretin-1 (n = 10). Controls were matched to each patient based on age, gender, and geographic location. Daytime sleepiness was assessed using the Epworth Sleepiness Level (ESS); mean score ( SEM) among controls was 5.7 0.3 (narcolepsy with cataplexy: 16.8 0.4, narcolepsy without cataplexy: 15.6 0.6). Nine controls with documented normal CSF hypocretin-1 were also included. The presence or absence of was decided using exon2 sequence specific primers8. Demographics and positivity for each subgroup are reported in Table 1. Local institutional review boards at each institution approved human protocols for the study. Written informed consent was obtained from all study participants. Table 1 Cases and controls used in the study was obtained by RT-PCR amplification of poly(A)+ RNA extracted from human hypothalamus (Takara Bio, Kyoto, Japan). cDNA was synthesized using ReverTraAce (TOYOBO, Tokyo, Japan) with random hexamer primers, according to the manufacturer’s instructions. The PCR amplification primers used were: 5-CGCGGATCCATGAACATACACAGGTCTA-3 and 5-CCGCTCGAGATTCTTGGCCAACTGTTCCTT-3 (PCR product was sub-cloned into a pET28a COL1A2 (+) expression vector (Novagen, Madison, WI, USA) to generate the TRIB2 expression vector (TRIB2/pET28a). Recombinant [35S]-TRIB2 Radioligand Binding Assay for Anti-TRIB2 Autoantibody Detection Recombinant [35S]-Methionine labeled TRIB2 was generated as explained previously.16 Briefly, the TNT quick couples system (Promega, Madison, WI, USA) was used to transcribe KC01 and translate labeled TRIB2 (with verification of a size of KC01 36 kDa) to be used as the antigen for the detection of serum autoantibodies in RLA. An anti-Trib2 mouse monoclonal IgG (Santa Cruz Biotechnology, Inc., Santa Cruz, CA, USA) was used as a positive control. Serum from controls and patients (1 L, 1:30, duplicate for each sample) was added to [35S]-TRIB2 for overnight incubation at 4C. Protein G was then added, and the reaction mixtures were filtered, allowing the retention of Protein G-antigen-autoantibody complexes around the filter (for counting) if present. Samples showing 10% coefficient of variance (CV) within duplicates were re-assayed. Final intra-assay CV was 0.0% to 9.4% and inter-assay CV was 1.3% to 8.8%. To reduce inter-assay variation, results were expressed as follows: cpm of each serum sample / cpm of 100 pooled healthy control sera, a measure we call the anti-TRIB2 autoantibody index. A measure of 1.0 thus represents the mean reactivity of a large number of control sera, with higher figures indicating increased presence of TRIB2 autoantibodies. Measurement of Anti-Streptolysin O Antibodies Anti-streptolysin O (ASO) antibody titers, a semi-quantitative measure of recent infection,17 were assayed in serum according to the manufacturer’Os instructions (Apogent, Lenexa, KS, USA). We retested all aged samples used in the previous study18 and tested more samples. Statistical Analyses The cutoff point was set.