Aim: 

Sporadic amyotrophic lateral sclerosis (SALS) is a motor neuron degenerative disease of unknown aetiology. Current hypothesis on SALS is that multiple genetic and environmental factors contribute to disease liability.

Methods: 

We have investigated the genes encoding for a3 and a4 subunits of neuronal nicotinic acetylcholine receptor (nAChR) in 115 patients affected by SALS and in 400 controls. We investigated whether the identified mutations altered the functional properties of nAChRs, using recombinant expression of asubunit mutations transiently expressed in HEK cells.

Results: 

In 5 over 115 patients missense mutations in genes encoding for a3 and a4 subunits of nAChRs have been identified. All mutations substituted an amino-acid in the cytosolic loop linking transmembrane domains M3-M4 of the subunit. NAChRs formed by mutant a and wild type (WT) b4 subunits did not show changes in channel unitary conductance and Ca²⁺ permeability, while they had an altered apparent affinity for the agonist nicotine (Nic) in comparison to WT-nAChR. Moreover mutant receptors displayed a strongly reduced use-dependent rundown of Nic-activated currents (INic), and a markedly reduced desensitization also coupled to a sustained level of intracellular Ca²⁺ concentration during agonist application, respect to WT-nAChR.

Conclusions: 

Mutations in genes encoding a3 and a4 subunits of nAChR were found in 4.3% of SALS patients. The identified mutations profoundly altered functional properties of nAChR in vitro, resulting in a sustained Ca²⁺ entry into cells. We suggest that the activity of these gain-of-function a?mutant nAChRs might contribute to neuronal death in a subset of SALS.