RESUMEN
INTRODUCTION: Genome-wide association studies (GWAS) are fundamental for identifying loci associated with diseases. However, they require replication in other ethnicities. METHODS: We performed GWAS on sporadic Alzheimer's disease (AD) including 539 patients and 854 controls from Argentina and Chile. We combined our results with those from the European Alzheimer and Dementia Biobank (EADB) in a meta-analysis and tested their genetic risk score (GRS) performance in this admixed population. RESULTS: We detected apolipoprotein E ε4 as the single genome-wide significant signal (odds ratio = 2.93 [2.37-3.63], P = 2.6 × 10-23 ). The meta-analysis with EADB summary statistics revealed four new loci reaching GWAS significance. Functional annotations of these loci implicated endosome/lysosomal function. Finally, the AD-GRS presented a similar performance in these populations, despite the score diminished when the Native American ancestry rose. DISCUSSION: We report the first GWAS on AD in a population from South America. It shows shared genetics modulating AD risk between the European and these admixed populations. HIGHLIGHTS: This is the first genome-wide association study on Alzheimer's disease (AD) in a population sample from Argentina and Chile. Trans-ethnic meta-analysis reveals four new loci involving lysosomal function in AD. This is the first independent replication for TREM2L, IGH-gene-cluster, and ADAM17 loci. A genetic risk score (GRS) developed in Europeans performed well in this population. The higher the Native American ancestry the lower the GRS values.
Asunto(s)
Enfermedad de Alzheimer , Azidas , Estudio de Asociación del Genoma Completo , Humanos , Chile , Enfermedad de Alzheimer/genética , Predisposición Genética a la Enfermedad/genética , Polimorfismo de Nucleótido Simple/genéticaRESUMEN
Rare coding variants in TREM2, PLCG2, and ABI3 were recently associated with the susceptibility to Alzheimer's disease (AD) in Caucasians. Frequencies and AD-associated effects of variants differ across ethnicities. To start filling the gap on AD genetics in South America and assess the impact of these variants across ethnicity, we studied these variants in Argentinian population in association with ancestry. TREM2 (rs143332484 and rs75932628), PLCG2 (rs72824905), and ABI3 (rs616338) were genotyped in 419 AD cases and 486 controls. Meta-analysis with European population was performed. Ancestry was estimated from genome-wide genotyping results. All variants show similar frequencies and odds ratios to those previously reported. Their association with AD reach statistical significance by meta-analysis. Although the Argentinian population is an admixture, variant carriers presented mainly Caucasian ancestry. Rare coding variants in TREM2, PLCG2, and ABI3 also modulate susceptibility to AD in populations from Argentina, and they may have a European heritage.
Asunto(s)
Proteínas Adaptadoras Transductoras de Señales/genética , Enfermedad de Alzheimer/etnología , Enfermedad de Alzheimer/genética , Glicoproteínas de Membrana/genética , Fosfolipasa C gamma/genética , Receptores Inmunológicos/genética , Anciano , Anciano de 80 o más Años , Argentina/etnología , Población Negra/genética , Femenino , Predisposición Genética a la Enfermedad , Variación Genética , Estudio de Asociación del Genoma Completo , Genotipo , Humanos , Indígenas Norteamericanos/genética , Masculino , Persona de Mediana Edad , Población Blanca/genéticaRESUMEN
Alzheimer's disease (AD) is characterized by amyloid beta (A beta) accumulation in the brain and is classified as familial early-onset (FAD) or sporadic late-onset (SAD). Evidences suggest that deficits in the brain expression of insulin degrading enzyme (IDE) and neprilysin (NEP), both proteases involved in amyloid degradation, may promote A beta deposition in SAD. We studied by immunohistochemistry IDE and NEP cortical expression in SAD and FAD samples carrying the E280A presenilin-1 missense mutation. We showed that IDE, a soluble peptidase, is linked with aggregated A beta 40 isoform while NEP, a membrane-bound protease, negatively correlates with amyloid angiopathy and its expression in the senile plaques is independent of aggregated amyloid and restricted to SAD cases. NEP, but not IDE, is over-expressed in dystrophic neurites, both proteases are immunoreactive in activated astrocytes but not in microglia and IDE was the only one detected in astrocytes of white matter from FAD cases. Collectively, our results support the notion that gross conformational changes involved in the modification from "natively folded-active" to "aggregated-inactive" IDE and NEP may be a relevant pathogenic mechanism in SAD.