Mutations in SLC25A1, encoding the mitochondrial citrate carrier, cause neuromuscular junction transmission defect

The mitochondrial citrate carrier (CIC) encoded by the SLC25A1 gene, catalyzes the export of citrate from mitochondria to the cytosol where it is broken into into acetyl-CoA and oxaloacetate. By exome sequencing we identified for the first time two pathogenic SLC25A1 variants in a patient that suffered from a severe neurodevelopmental syndrome. More recently we reported a novel homozygous mutation in the SLC25A1 gene in an affected sib pair. Both patients presented with myasthenia and impaired neuromuscular junction (NMJ) transmission whilst no neurodevelopment disorder has been observed[1]. Functional analysis of the pathogenic mutations has been performed upon reconstitution of recombinant proteins into liposomes. Interestingly, the newly identified mutation caused a milder activity impairment than the previously reported mutations suggesting a fundamental role of CIC in NM transmission whose defect was previously masked by the harsher phenotype. Knocking down the SLC25A1 orthologues in zebrafish embryos we observed abnormalities in the NMJ with an erratic outgrowth of neuronal axons toward muscle fiber. Using the CRISPR/CAS9 approach we obtained stable lines of C.elegans knocked-out in the SLC25A1 ortholog that showed partial resistance to Aldicarb, a specific inhibitor of cholinesterase activity that causes the paralysis of the worms. Altogether our data point to a key role of CIC in NMJ transmission most likely due to the requirement of acetyl-CoA supply for acetylcholine synthesis at the pre-synaptic nerve terminal.