The cholinesterase investigation unit (CIU) conducts pharmacogenetic analyses and provides both biochemical and molecular (DNA) services. Routinely available are phenotyping and genotyping of the enzyme butyrylcholinesterase (BChE), and molecular diagnosis of Gilbert’s syndrome.
BChE is an enzyme responsible for the metabolism of the muscle relaxants suxamethonium (scoline) and mivacurium that shows a great deal of genetic variation. Some variants lead to an effective enzyme deficiency which impairs an individual’s ability to metabolise the drugs and leads to prolonged paralysis and apnoea.
Biochemical phenotypes of BChE are identified by inhibitor studies with agents such as dibucaine and fluoride, but where more detailed information is required DNA studies are often of value. Genotypes are determined using heteroduplex analysis, and examine approximately 70% of the gene, identifying at least 18 of the known and "named" variants. Further analysis (including sequencing) is also performed where necessary or indicated by clinical or family history.
All reports are issued with interpretative comments and, in the case of BChE, an assessment of risk (of suxamethonium sensitivity). Warning cards are issued for patients likely to be sensitive to suxamethonium and recommendations given with the report on the need for family studies.