The second discovered ADNFLE mutation was also in "CHRNA4". This mutation, L259_I260insL, is caused by the insertion of three nucleotides (GCT) between a stretch of leucine amino acids and an isoleucine. As with the S248F mutation, the L259_I260insL mutation is located in the second transmembrane spanning region. Electrophysiological experiments have shown that this mutant is tenfold more sensitive to acetylcholine than wild-type. Calcium permeability, however is notably decreased in mutant compared to wild-type containing receptors. Furthermore, this mutant shows slowed desensitization compared to both wild-type and S248F mutant receptors.