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A large GGGGCC-repeat expansion mutation (HREM) in C9orf72 is the most common known cause of ALS and FTD in European populations. Sequence variations immediately downstream of the HREM region have previously been observed and have been suggested to be one reason for difficulties in interpreting RP-PCR data. Our objective was to determine the properties of these sequence variations with regard to prevalence, the range of variation, and effect on disease prognosis. We screened a multi-national cohort (n = 6981) for the HREM and samples with deviant RP-PCR curves were identified. The deviant samples were subsequently sequenced to determine sequence alteration. Our results show that in the USA and European cohorts (n = 6508) 10.7% carried the HREM and 3% had a sequence variant, while no HREM or sequence variants were observed in the Japanese cohort (n = 473). Sequence variations were more common on HREM alleles; however, certain population specific variants were associated with a non-expanded allele.In conclusion, we identified 38 different sequence variants, most located within the first 50 bp downstream of the HREM region. Furthermore, the presence of an HREM was found to be coupled to a lower age of onset and a shorter disease survival, while sequence variation did not have any correlation with these parameters. [ABSTRACT FROM AUTHOR]

Background The GGGGCC-repeat expansion in C9orf72 is the most frequent mutation found in patients with amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Most of the studies on C9orf72 have relied on repeat-primed PCR (RP-PCR) methods for detection of the expansions. To investigate the inherent limitations of this technique, we compared methods and results of 14 laboratories. Methods The 14 laboratories genotyped DNA from 78 individuals (diagnosed with ALS or FTD) in a blinded fashion. Eleven laboratories used a combination of amplicon-length analysis and RP-PCR, whereas three laboratories used RP-PCR alone; Southern blotting techniques were used as a reference. Results Using PCR-based techniques, 5 of the 14 laboratories got results in full accordance with the Southern blotting results. Only 50 of the 78 DNA samples got the same genotype result in all 14 laboratories. There was a high degree of false positive and false negative results, and at least one sample could not be genotyped at all in 9 of the 14 laboratories. The mean sensitivity of a combination of amplicon-length analysis and RP-PCR was 95.0% (73.9-100%), and the mean specificity was 98.0% (87.5-100%). Overall, a sensitivity and specificity of more than 95% was observed in only seven laboratories. Conclusions Because of the wide range seen in genotyping results, we recommend using a combination of amplicon-length analysis and RP-PCR as a minimum in a research setting. We propose that Southern blotting techniques should be the gold standard, and be made obligatory in a clinical diagnostic setting. [ABSTRACT FROM AUTHOR]

Abstract: Profilin 1 is a central regulator of actin dynamics. Mutations in the gene profilin 1 (PFN1) have very recently been shown to be the cause of a subgroup of amyotrophic lateral sclerosis (ALS). Here, we performed a large screen of US, Nordic, and German familial and sporadic ALS and frontotemporal dementia (FTLD) patients for PFN1 mutations to get further insight into the spectrum and pathogenic relevance of this gene for the complete ALS/FTLD continuum. Four hundred twelve familial and 260 sporadic ALS cases and 16 ALS/FTLD cases from Germany, the Nordic countries, and the United States were screened for PFN1 mutations. Phenotypes of patients carrying PFN1 mutations were studied. In a German ALS family we identified the novel heterozygous PFN1 mutation p.Thr109Met, which was absent in controls. This novel mutation abrogates a phosphorylation site in profilin 1. The recently described p.Gln117Gly sequence variant was found in another familial ALS patient from the United States. The ALS patients with mutations in PFN1 displayed spinal onset motor neuron disease without overt cognitive involvement. PFN1 mutations were absent in patients with motor neuron disease and dementia, and in patients with only FTLD. We provide further evidence that PFN1 mutations can cause ALS as a Mendelian dominant trait. Patients carrying PFN1 mutations reported so far represent the “classic” ALS end of the ALS-FTLD spectrum. The novel p.Thr109Met mutation provides additional proof-of-principle that mutant proteins involved in the regulation of cytoskeletal dynamics can cause motor neuron degeneration. Moreover, this new mutation suggests that fine-tuning of actin polymerization by phosphorylation of profilin 1 might be necessary for motor neuron survival. [Copyright &y& Elsevier]