RESUMEN
The majority of individuals in the chronic phase of Chagas disease are asymptomatic (indeterminate form). Every year 2-3% of these individuals develop severe clinical manifestations (cardiac and digestive forms). In this study a Trypanosoma cruzi DNA microarray was used to compare the transcript profiles of six human isolates: three from asymptomatic and three from cardiac patients. Seven signals were expressed differentially between the two classes of isolates, including tryparedoxin, surface protease GP63, cyclophilin, some hypothetical proteins and the pre-edited maxicircle gene NADH dehydrogenase subunit 7 (ND7). The approximately 30-fold greater signal in cardiac strains for ND7 was the most pronounced of the group, and differential levels of pre-edited ND7 transcript confirmed the microarray analysis. The ND7 gene from asymptomatic isolates showed a deletion of 455bp from nt 222 to nt 677 relative to ND7 of the CL Brener reference strain. The ND7 gene structure correlated with disease manifestation for 20 isolates from clinically characterised, chronic phase patients. The ND7 lesion produces a truncated product that could impair the function of mitochondrial complex I. Possible links between the integrity of the electron transport chain and symptom presentation are discussed. We propose that ND7 and other genes of the pathway constitute valuable targets for PCR assays in the differential diagnosis of the infective T. cruzi strain. While this hypothesis requires validation by the examination of additional recent parasite isolates from patients with defined pathologies, the identification of specific molecular markers represents a promising advance in the association between parasite genetics and disease pathology.
Asunto(s)
Cardiomiopatía Chagásica/parasitología , Enfermedad de Chagas/parasitología , ADN de Cinetoplasto/genética , Eliminación de Gen , Proteínas de la Membrana/genética , Proteínas Protozoarias/genética , Trypanosoma cruzi/genética , Adolescente , Adulto , Animales , Femenino , Perfilación de la Expresión Génica , Regulación de la Expresión Génica , Humanos , Masculino , Persona de Mediana Edad , Datos de Secuencia Molecular , NADH Deshidrogenasa/genética , Análisis de Secuencia por Matrices de OligonucleótidosRESUMEN
One of the goals of gene expression experiments is the identification of differentially expressed genes among populations that could be used as markers. For this purpose, we implemented a model-free Bayesian approach in a user-friendly and freely available web-based tool called BayBoots. In spite of a common misunderstanding that Bayesian and model-free approaches are incompatible, we merged them in the BayBoots implementation using the Kernel density estimator and Rubin 's Bayesian Bootstrap. We used the Bayes error rate (BER) instead of the usual P values as an alternative statistical index to rank a class marker's discriminative potential, since it can be visualized by a simple graphical representation and has an intuitive interpretation. Subsequently, Bayesian Bootstrap was used to assess BER 's credibility. We tested BayBoots on microarray data to look for markers for Trypanosoma cruzi strains isolated from cardiac and asymptomatic patients. We found that the three most frequently used methods in microarray analysis: t-test, non-parametric Wilcoxon test and correlation methods, yielded several markers that were discarded by a time-consuming visual check. On the other hand, the BayBoots graphical output and ranking was able to automatically identify markers for which classification performance was consistent. BayBoots is available at: http://www.vision.ime.usp.br/~rvencio/BayBoots.
