RESUMEN
Large expansions of hexanucleotide GGGGCC (G4C2) repeats (hundreds to thousands) in the first intron of the chromosome 9 open reading frame 72 (C9orf72) locus are the strongest known genetic factor associated with amyotrophic lateral sclerosis and frontotemporal lobar degeneration. Different hypotheses exist about the underlying disease mechanism including loss of function by haploinsufficiency, toxicity arising as a result of RNA or dipeptide repeats (DPRs). Five different DPRs are produced by repeat-associated non-ATG-initiated translation of the G4C2 repeats. Though earlier studies have indicated toxicity of the DPRs in worms, flies, primary cultured cells and cell lines, the effect of expressing DPRs of amyotrophic lateral sclerosis-relevant length has not been tested on motor behaviour in vertebrate models. In this study, by expressing constructs with alternate codons encoding different lengths of each DPR (40, 200 and 1000) in the vertebrate zebrafish model, the GR DPR was found to lead to the greatest developmental lethality and morphological defects, and GA, the least. However, expressing 1000 repeats of any DPR, including the 'non-toxic' GA DPR led to locomotor defects. Based on these observations, a transgenic line stably expressing 100 GR repeats was generated to allow specific regional and temporal expression of GR repeats in vivo. Expression of GR DPRs ubiquitously resulted in severe morphological defects and reduced swimming. However, when expressed specifically in motor neurons, the developmental defects were significantly reduced, but the swimming phenotype persisted, suggesting that GR DPRs have a toxic effect on motor neuron function. This was validated by the reduction in motor neuron length even in already formed motor neurons when GR was expressed in these. Hence, the expression of C9orf72-associated DPRs can cause significant motor deficits in vertebrates.
Asunto(s)
Esclerosis Amiotrófica Lateral/genética , Proteína C9orf72/genética , Expansión de las Repeticiones de ADN/genética , Degeneración Lobar Frontotemporal/genética , Esclerosis Amiotrófica Lateral/fisiopatología , Animales , Animales Modificados Genéticamente/genética , Dipéptidos/genética , Modelos Animales de Enfermedad , Degeneración Lobar Frontotemporal/fisiopatología , Regulación de la Expresión Génica , Humanos , Locomoción/genética , Locomoción/fisiología , Neuronas Motoras/patología , Neuronas Motoras/fisiología , Pez Cebra/genéticaRESUMEN
Mutations in the gene p62/SQSTM1 have been reported as a relatively rare cause of frontotemporal lobar degeneration (FTLD). To establish whether this was the case for cases of FTLD from the United Kingdom, we sequenced the sequenced the entire open reading frame of this gene in a large cohort of patients. We identified 3 novel mutations in p62/SQSTM1 in 4 patients. One of these was a premature stop codon that removed the last 101 amino acids of the protein that presumably has a negative effect on protein function. Another mutation was also found in a case with a repeat expansion mutation in C9orf72 confirmed by Southern blot. These findings confirm a role of p62/SQSTM1 as a cause of FTLD.
Asunto(s)
Proteínas Adaptadoras Transductoras de Señales/genética , Degeneración Lobar Frontotemporal/genética , Estudios de Asociación Genética , Predisposición Genética a la Enfermedad/genética , Mutación/genética , Proteínas Adaptadoras Transductoras de Señales/química , Adulto , Anciano , Anciano de 80 o más Años , Aminoácidos/genética , Proteína C9orf72 , Codón sin Sentido/genética , Estudios de Cohortes , Expansión de las Repeticiones de ADN/genética , Femenino , Humanos , Masculino , Persona de Mediana Edad , Sistemas de Lectura Abierta/genética , Proteínas/genética , Proteína Sequestosoma-1 , Reino UnidoRESUMEN
Frontotemporal lobar degeneration (FTLD) is a highly familial neurodegenerative disease. It has recently been shown that the most common genetic cause of FTLD and amyotrophic lateral sclerosis (ALS) is a hexanucleotide repeat expansion in C9ORF72. To investigate whether this expansion was specific to the FTLD/ALS disease spectrum, we genotyped the hexanucleotide repeat region of C9ORF72 in a large cohort of patients with Alzheimer's disease (AD). A normal range of repeats was found in all cases. We conclude that the hexanucleotide repeat expansion is specific to the FTLD/ALS disease spectrum.
Asunto(s)
Enfermedad de Alzheimer/genética , Degeneración Lobar Frontotemporal/genética , Predisposición Genética a la Enfermedad/genética , Nucleótidos/genética , Proteínas/genética , Secuencias Repetitivas de Ácidos Nucleicos/genética , Adulto , Anciano , Enfermedad de Alzheimer/epidemiología , Proteína C9orf72 , Comorbilidad , Femenino , Degeneración Lobar Frontotemporal/epidemiología , Marcadores Genéticos/genética , Humanos , Masculino , Persona de Mediana Edad , Prevalencia , Factores de Riesgo , Reino Unido/epidemiologíaRESUMEN
The chromosome 9p21 amyotrophic lateral sclerosis-frontotemporal dementia (ALS-FTD) locus contains one of the last major unidentified autosomal-dominant genes underlying these common neurodegenerative diseases. We have previously shown that a founder haplotype, covering the MOBKL2b, IFNK, and C9ORF72 genes, is present in the majority of cases linked to this region. Here we show that there is a large hexanucleotide (GGGGCC) repeat expansion in the first intron of C9ORF72 on the affected haplotype. This repeat expansion segregates perfectly with disease in the Finnish population, underlying 46.0% of familial ALS and 21.1% of sporadic ALS in that population. Taken together with the D90A SOD1 mutation, 87% of familial ALS in Finland is now explained by a simple monogenic cause. The repeat expansion is also present in one-third of familial ALS cases of outbred European descent, making it the most common genetic cause of these fatal neurodegenerative diseases identified to date.