The classification of esterases: an important gene family involved in insecticide resistance - A review

The use of chemical insecticides continues to play a major role in the control of disease vector populations, which is leading to the global dissemination of insecticide resistance. A greater capacity to detoxify insecticides, due to an increase in the expression or activity of three major enzyme families, also known as metabolic resistance, is one major resistance mechanisms. The esterase family of enzymes hydrolyse ester bonds, which are present in a wide range of insecticides; therefore, these enzymes may be involved in resistance to the main chemicals employed in control programs. Historically, insecticide resistance has driven research on insect esterases and schemes for their classification. Currently, several different nomenclatures are used to describe the esterases of distinct species and a universal standard classification does not exist. The esterase gene family appears to be rapidly evolving and each insect species has a unique complement of detoxification genes with only a few orthologues across species. The examples listed in this review cover different aspects of their biochemical nature. However, they do not appear to contribute to reliably distinguish among the different resistance mechanisms. Presently, the phylogenetic criterion appears to be the best one for esterase classification. Joint genomic, biochemical and microarray studies will help unravel the classification of this complex gene family.

Multigenerational Brazilian family with malignant hyperthermia and a novel mutation in the RYR1 gene

Malignant hyperthermia (MH) is a pharmacogenetic disease triggered in susceptible individuals by the administration of volatile halogenated anesthetics and/or succinylcholine, leading to the development of a hypermetabolic crisis, which is caused by abnormal release of Ca2+ from the sarcoplasmic reticulum, through the Ca2+ release channel ryanodine receptor 1 (RyR1). Mutations in the RYR1 gene are associated with MH in the majority of susceptible families. Genetic screening of a 5-generation Brazilian family with a history of MH-related deaths and a previous MH diagnosis by the caffeine halothane contracture test (CHCT) in some individuals was performed using restriction and sequencing analysis. A novel missense mutation, Gly4935Ser, was found in an important functional and conserved locus of this gene, the transmembrane region of RyR1. In this family, 2 MH-susceptible individuals previously diagnosed with CHCT carry this novel mutation and another 24 not previously diagnosed members also carry it. However, this same mutation was not found in another MH-susceptible individual whose CHCT was positive to the test with caffeine but not to the test with halothane. None of the 5 MH normal individuals of the family, previously diagnosed by CHCT, carry this mutation, nor do 100 controls from control Brazilian and USA populations. The Gly4932Ser variant is a candidate mutation for MH, based on its co-segregation with disease phenotype, absence among controls and its location within the protein.