Abnormal enzyme phenotype (e1a e1f): Normal response to succinylcholine

The enzyme serum cholinesterase responsible for the hydrolysis of the muscle relaxant succinylcholine exists in the form of several variants. These may be identified in serum by using substances which inhibit their activity to different degrees. The heterozygote for the atypical and fluoride resistant enzymes (E1a E1f) is one of the phenotypes which has been reported to be sensitive to succinylcholine.A case is described where succinylcholine given on two separate occasions did not induce apnoea in an individual phenotyped as E1a E1a by at least five methods of inhibition. This is the first reported example of such insensitivity to the drug in this phenotype.Temperature activities for the patient’s serum over the range of 20° C to 45° C differed from that of an established E1a Eif phenotype used as a control. There was a progressive inactivation of the control serum at temperatures higher than 35° C, as previously reported for this phenotype. Activity in the serum of the subject of this study did not exhibit the peak activity at 35° C but continued to rise and probably reached a peak between 40° C and 45° C.The significance of these results in the context of current methods of phenotyping is discussed.