Genetic and immunological analyses of patients with increased serum butyrylcholinesterase activity and its C5 variant form.

ABSTRACT

Recent evidence has denied genetic abnormality as a mechanism of the C5 variant of butyrylcholinesterase (BChE) and proposed the binding of an unknown protein with the C4 component. The present study aimed to evaluate whether the coding sequences and non-translated sequences of the BChE gene at exons 1 to 4, 3q are structurally different in subjects having elevated BChE with and without the C5 variant phenotype. We also attempted to identify the unknown protein associated with the C5 variant and measured the BChE-specific activity in the C5 variant with an enzyme-linked immunosorbent assay (ELISA) using anti-BChE monoclonal antibody. We investigated five subjects, four of whom had elevated plasma BChE (three C5-positive [C5(+)] and one C5-negative [C5(-)]) and one control with a normal plasma BChE level. Direct DNA sequencing of the BChE gene revealed no relevant genetic mutations and no abnormal migrations in the genes of all five subjects. Precipitation of the patients' sera with anti-human immunoglobulin A (IgA), -IgG, -IgM, anti-human albumin antibodies had no effect on the BChE activity. The measured BChE activity in C5(+) was 30 to 54% higher than the activity calculated from BChE protein content. The present results suggest that the C5(+) phenotype is not associated with any genetic abnormality in the CHE1 locus, and BChE-specific activity is enhanced in the C5(+) variant. However, the exact nature of the unknown protein related to the C5(+) phenotype remains unclear.