UBQLN2 Mutations in ALS and ALS/Dementia: A Genetic, Functional and Histopathological Analysis (S05.006) (2012)

Objective: To identify the genetic defect causing dominant X-linked ALS and ALS/dementia, and characterize the functional and pathological determinants. Background Most cases of ALS are sporadic but about 5-10% are familial. Mutations in SOD1, TDP43 and FUS account for approximately 30% of classic familial ALS. The causes of the remaining cases of familial ALS and of the vast majority of sporadic ALS are unknown. Despite extensive studies of previously identified ALS-causing genes, the pathogenic mechanism underlying motor-neuron degeneration in ALS remains largely obscure. Dementia, usually of the frontotemporal lobar type, may occur in some ALS cases. It is unclear whether ALS and dementia share common aetiology and pathogenesis in ALS/dementia. More than a decade ago, we had linked a large ALS family to the pericentric region of the X chromosome. Design/Methods: Detailed mapping was done with dense microsatellite markers and Illumina Sentrix HumanHap300 Genotyping BeadChip. Candidate genes were sequenced using Beckman Coulter CEQ 8000 DNA analysis system. Immunohistochemistry and light and confocal microscopy were performed according to standard protocols. Neuro2a and SHSY-5Y cells were transiently co-transfected with a ubiquitin-proteasome system (UPS) reporter plasmid (Ub-G76V-GFP) and pIRES2-DsRed2 dual expression vectors containing either wildtype or mutant UBQLN2 and analyzed using a MoFlo cell sorter and Summit software. Results: We show mutations of ubiquilin2, a ubiquitin-like protein, in five families with ALS and ALS/dementia. We also show that inclusions containing ubiquilin2 are a common pathological feature in a wide spectrum of ALS and ALS/dementia. Functional studies indicate an impairment of ubiquitin-mediated proteasomal degradation in cells expressing mutant ubiquilin2. Conclusions: These data provide evidence for an impairment of protein turnover in the pathogenesis of ALS and ALS/dementia. Further elucidation of these processes may be central to the understanding of pathogenic pathways. These pathways should provide novel molecular targets for the design of rational therapies for these disorders. Supported by: The National Institute of Neurological Disorders and Stroke (NS050641), the Les Turner ALS Foundation, the Vena E. Schaff ALS Research Fund, the Harold Post Research Professorship, the Herbert and Florence C. Wenske Foundation, the David C. Asselin MD Memorial Fund, the Help America Foundation and the Les Turner ALS Foundation/Herbert C. Wenske Foundation Professorship. F.F. has support from NIH (T32 AG20506). K.A. is a postdoctoral fellow of the Blazeman Foundation for ALS. G.H.G. received travel funds from MND Scotland. Disclosure: Dr. Fecto has nothing to disclose. Dr. Deng has nothing to disclose. Dr. Chen has nothing to disclose. Dr. Hong has nothing to disclose. Dr. Boycott has nothing to disclose. Dr. Gorrie has nothing to disclose. Dr. Siddique has nothing to disclose. Dr. Yang has nothing to disclose. Dr. Shi has nothing to disclose. Dr. Zhai has nothing to disclose. Dr. Jiang has nothing to disclose. Dr. Hirano has nothing to disclose. Dr. Rampersaud has nothing to disclose. Dr. Jansen has nothing to disclose. Dr. Donkervoort has nothing to disclose. Dr. Bigio has nothing to disclose. Dr. Brooks has received personal compensation for activities with Avanir Pharmaceuticals, Bayer Healthcare Pharmaceuticals, Biogen Idec, Genentech, Inc., and Teva Neuroscience. Dr. Brooks has received research support from Avanir Pharmaceuticals, Biogen Idec, NINDS, Novartis, and Teva Neuroscience. Dr. Ajroud has nothing to disclose. Dr. Sufit has nothing to disclose. Dr. Haines has nothing to disclose. Dr. Mugnaini has nothing to disclose. Dr. Pericak-Vance has nothing to disclose. Dr. Siddique has nothing to disclose.