Plasma cholinesterase variants - an unexpectedly high incidence of the silent allele.

The silent allele is one of the rarer plasma cholinesterase variants. In a series of 9 South African families with an inherited abnormal cholinesterase, the silent allele occurs in 5. In 2 it is the only abnormal allele present while in 3 it occurs with the 'atypical' (dibucaine-resistant) form. Identification of the single silent allele requires full family studies, since its inhibition characteristics are those of the other allele present, normal or abnormal.