Genome-wide Association Study Identifies Two Loci Influencing Plasma Neurofilament Light Levels

Objective:Plasma neurofilament light（NFL）is the main component of neurofilaments,which are predominantly localized in large-caliber myelinated axons.The damage of axons leads to releasing NFL into CSF and plasma.The elevated CSF NFL and plasma NFL levels in Alzheimer disease（AD）patients suggest that axonal damage and neuronal loss may play a vital role in the pathogenesis of AD.As a promising biomarker for AD,plasma NFL increases at the early stage of AD and is associated with its progression.The diagnostic accuracy of AD was equivalent to the core cerebrospinal fluid biomarkers of AD including total-tau protein,phosphorylated-tau protein,and Aβ42.Genome-wide association study using these cerebrospinal fluid biomarkers have identified several risk loci influencing AD onset.We performed a genome-wide association study（GWAS）of plasma NFL in Alzheimer’s Disease Neuroimaging Initiative（ADNI）cohort to identify novel variants associated with AD.Methods:This study included 179 cognitive healthy controls（HC）,176 patients with mild cognitive impairment（MCI）,and 172 patients with AD.All subjects were restricted to non-Hispanic Caucasian derived from the ADNI cohort and met all quality control（QC）criteria.Association of plasma NFL with the genetic variants was assessed using PLINK with an additive genetic model,i.e.dose-dependent effect of the minor allele,with the following stringent criteria:minimum call rate for single nucleotide polymorphisms（SNPs）and individuals>98%,minimum minor allele frequencies（MAF）>0.20,Hardy-Weinberg equilibrium test P>0.001.The influence of plasma NFL associated genetic variants（rs7943454）on brain structure was further assessed using PLINK with a linear regression model.Differences in continuous variables（plasma NFL levels,volume of regional brain）were examined using one-way analysis of variance（ANOVA）,and Tukey’s multiple comparisons test was used to perform pairwise analysis after ANOVA.Results:AD patients had higher plasma NFL levels compared with MCI subjects and HC（P<0.0001）.MCI group also had higher plasma NFL levels compared to HC（P=0.0007）.CSF NFL levels showed positive correlation with plasma NFL levels in different diagnostic groups.CSF NFL versus plasma NFL:AD（r=0.364,P=0.001）,MCI（r=0.560,P<0.001）,HC（r=0.471,P<0.001）.The minor allele（T）of rs7943454 in leucine zipper protein 2 gene（LUZP2）was associated with higher plasma NFL at suggestive levels(P=1.39×10^-6)in a dose-dependent fashion.In contrast,the minor allele（G）of rs640476 near GABRB2 was associated with lower plasma NFL at suggestive levels(P=6.71×10^-6)in a dose-dependent effect in all diagnostic groups except the MCI group.Furthermore,the minor allele（T）of rs7943454 within LUZP2 increased the onset risk of AD（odds ratio=1.547,confidence interval 95%=1.018-2.351）and was associated with atrophy of right middle temporal gyrus in the whole cohort in the longitudinal study（P=0.0234）.Conclusion:GWAS found that two single nucleotide polymorphisms（rs7943454 and rs640476）were associated with plasma NFL at suggestive levels.Rs7943454 in LUZP2was associated with the onset risk of AD and atrophy of right middle temporal gyrus in the whole cohort.Using an endophenotype-based approach,we identified rs7943454 as a new AD risk locus.