While loss of both NTE alleles resulted in embryolethality, heterozygous (Nte+/−) mice were viable and fertile [103]. Nte+/− mice had 40% less brain NTE activity than wild-type mice, but equal brain AChE activity. Nte+/− mice also displayed a phenotype of hyperactivity, which is not directly relevant to OPIDP, and were more sensitive to the acute toxicity of ethyl octophosphoro-fluoridate (EOPF), an OPIDP-causing OP [103]. Following administration of a low dose of EOPF, Nte+/− mice showed a further increased locomotor activity, but NTE activity was not quantified in these animals [103].the CNS [106].