Identification of a novel mutation in MEF2C gene in an atypical patient with frontotemporal lobar degeneration.

The MEF2C gene encodes a transcription factor known to play a crucial role in molecular pathways affecting neuronal development. MEF2C mutations were described as a genetic cause of developmental disease (MRD20), and several reports sustain its involvement in dementia-related conditions, such as Alzheimer's disease and amyotrophic lateral sclerosis. These pathologies and frontotemporal degeneration (FTLD) are thought to share common physiopathological pathways. In this exploratory study, we searched for alterations in the DNA sequence of exons and boundaries, including 5'- and 3'-untranslated regions (5'UTR, 3'UTR), of MEF2C gene in 11 patients with clinical phenotypes related with MRD20 or FTLD. We identified a heterozygous deletion of 13 nucleotides in the 5'UTR region of a 69 years old FTLD patient. This alteration was absent in 200 healthy controls, suggesting a contribution to this patient's disease phenotype. In silico analysis of the mutated sequence indicated changes in mRNA secondary structure and stability, thus potentially affecting MEF2C protein levels. Furthermore, in vitro functional analysis of this mutation revealed that the presence of this deletion abolished the transcriptional activity of the gene in human embryonic cells and rat brain neurons, probably by modifying MEF2C expression. Altogether, our results provide evidence for the involvement of MEF2C in FTLD manifesting with seizures.