Detection of a novel frameshift mutation and regions with homozygosis within ARHGEF28 gene in familial amyotrophic lateral sclerosis

Abstract

Rho guanine nucleotide exchange factor (RGNEF) is a novel NFL mRNA destabilizing factor that forms neuronal cytoplasmic inclusions in spinal motor neurons in both sporadic (SALS) and familial (FALS) ALS patients. Given the observation of genetic mutations in a number of mRNA binding proteins associated with ALS, including TDP-43, FUS/TLS and mtSOD1, we analysed the ARHGEF28 gene (approx. 316 kb) that encodes for RGNEF in FALS cases to determine if mutations were present. We performed genomic sequencing, copy number variation analysis using TaqMan real-time PCR and spinal motor neuron immunohistochemistry using a novel RGNEF antibody. In this limited sample of FALS cases (n=7) we identified a heterozygous mutation that is predicted to generate a premature truncated gene product. We also observed extensive regions of homozygosity in the ARHGEF28 gene in two FALS patients. In conclusion, our findings of genetic alterations in the ARHGEF28 gene in cases of FALS suggest that a more comprehensive genetic analysis would be warranted.

The emerging role of guanine nucleotide exchange factors in ALS and other neurodegenerative diseases

“…For instance, while the loss of NEFL mRNA stability is critical to the formation of pathological NCIs in spinal motor neurons, the concomitant loss of GEF activity due to RGNEF sequestration may be sufficient to render the cell incapable of responding to the subsequent cellular stressors. Such a conceptualization is consistent with the increasing evidence for oligogenic inheritance in ALS where a second gene might participate as a critical modulator of the pathological phenotype of the disease (van Blitterswijk et al, 2012; Droppelmann et al, 2013b). In this context, perturbations in the function of GEF proteins might well be considered as key candidates for this “second hit” because of their direct or indirect roles on cell survival (Chen et al, 2002, 2009; Wu et al, 2003; Cai et al, 2005; Dietrich et al, 2005; Crittenden et al, 2010; Bai et al, 2013; Namekata et al, 2013).…”

“…Moreover, we and others found a heterozygous frameshift mutation in ARHGEF28 in both fALS and sALS patients that predicts the expression of a truncated protein by the mutated allele (Droppelmann et al, 2013b; Ma et al, 2014). …”

A novel small molecule HSP90 inhibitor, NXD30001, differentially induces heat shock proteins in nervous tissue in culture and in vivo

“…About 90 % of cases occur sporadically (sALS). The remainder are clearly familial (fALS; Valdmanis et al 2009); the genetic loci identified include genes encoding Cu/Zn-superoxide dismutase (SOD1; Rosen et al 1993), TAR DNA-binding protein 43 (Neumann et al 2006;Arai et al 2006), fused in sarcoma/ translated in liposarcoma (FUS; Kwiatkowski et al 2009;Vance et al 2009), vesicle-associated membrane protein B (Nishimura et al 2004), ubiquilin2 (Deng et al 2011), C9ORF72 (Renton et al 2011;Dejesus-Hernandez et al 2011), p62 (Hirano et al 2013), profilin 1 (Daoud et al 2013) , and RGNEF, a rhoGEF nucleotide exchange factor (Droppelmann et al 2013). Aside from sporadic ALS, this multiplicity of fALS-associated genes points to ALS being a syndrome with multiple initiating factors, yet there are commonalities in the manifestation of disease in patients with either familial or sporadic disease including formation of inclusions, unfolded protein responses, excitotoxicity, calcium dysregulation, mitochondrial dysfunction, oxidative stress, axonal transport defects, disruption of neuromuscular junctions, altered RNA metabolism, disruption of neuron-glia interactions, and inflammatory responses (Boillee et al 2006).…”

Genetic and epigenetic study of ALS-discordant identical twins with double mutations inSOD1andARHGEF28

“…Although p.T137A was in silico predicted to be damaging, 1 it would be important to obtain autopsy results to verify if the mutation leads to misfolded SOD1. 2 Intriguingly, the unaffected twin had a younger DNAm age than the affected twin, who had a more prominent history of narcotics abuse and head injury. A similar observation was obtained for the ALS-discordant C9orf72 MZ twins, for whom some environmental factors (smoking and head injury) were suspected to be modifying factors.…”