| Species | Original | Mutated to | Mutation |
| Human | Cys 128 | Ser | |
| Rat Equivalent | Cys 103 | ||
| Mouse Equivalent | Cys 103 |
This mutation causes the disulfide bond of the cysteine loop to not form which prevents association of a and e subunits. This mutation fails to incorporate into cell-surface pentamers and is therefore classified as a null mutation.
This mutation was found in patients with myasthenic syndrome.