A new point mutation in cholinesterase: relationship between multiple mutation sites and enzyme activity

A new mutation site has been found in a case of cholinesterase (ChE) deficiency diagnosed upon routine blood screening. Genomic DNA was sequenced and four point mutations were found: P1 (exon 2) nucleotide 298 (CCA-TCA), codon 100 (proline-serine), which is a novel mutation site; P4 (exon 2) nucleotide 1410 (CGT-CGG), codon 470 (arginine not changed); PS (exon 3) nucleotide 1543 (CGT-TGT), codon 515 (arginine-threonine); and P6 (exon 4) nucleotide 1615 (GCA-ACA), codon 539 (alanine-threonine). The patient had three (P1, P5, P6) heterozygous and one (P4) homozygous mutations. The three other family members studied had one (P1) or two (P5 and 6) heterozygous mutations in addition to a P4 homozygous mutation but their serum levels of ChE were normal or only slightly decreased. We concluded that three simultaneous mutations at codons 298, 1543 and 1615 are required to reduce serum ChE activity and that the single mutation at codon 298 or two mutations at codon 1543 and 1615 are not enough to reduce ChE activity.