A C6orf10/LOC101929163 locus is associated with age of onset in C9orf72 carriers

The G4C2-repeat expansion in C9orf72 is the most common known cause of amyotrophic lateral sclerosis and frontotemporal dementia. The high phenotypic heterogeneity of C9orf72 patients includes a wide range in age of onset, modifiers of which are largely unknown. Age of onset could be influenced by environmental and genetic factors both of which may trigger DNA methylation changes at CpG sites. We tested the hypothesis that age of onset in C9orf72 patients is associated with some common single nucleotide polymorphisms causing a gain or loss of CpG sites and thus resulting in DNA methylation alterations. Combined analyses of epigenetic and genetic data have the advantage of detecting functional variants with reduced likelihood of false negative results due to excessive correction for multiple testing in genome-wide association studies. First, we estimated the association between age of onset in C9orf72 patients (n = 46) and the DNA methylation levels at all 7603 CpG sites available on the 450 k BeadChip that are mapped to common single nucleotide polymorphisms. This was followed by a genetic association study of the discovery (n = 144) and replication (n = 187) C9orf72 cohorts. We found that age of onset was reproducibly associated with polymorphisms within a 124.7 kb linkage disequilibrium

Genomic analysis of recombinant Sabin clinical isolates

Recombination in Poliovirus vaccine strains is a very frequent phenomenon. In this report 23 polio/Sabin strains isolated from healthy vaccinees or from VAPP patients after OPV administration, were investigated in order to identify recombination sites from 2C to 3D regions of the poliovirus genome. RT-PCR, followed by Restriction Fragment Length Polymorphism (RFLP) screening analysis were applied in four distant genomic regions (5' UTR, VP1, 2C and 3C-3D) in order to detect any putative recombinant. The detected recombinants were sequenced from 2C to the end of the genome (3' UTR) and the exact recombination sites were determined with computational analysis. Five of the 23 isolated strains were recombinant in one genomic region, two of them in 2C, isolates EP16:S3/S2, EP23:S3/S1, two in 3D isolates EP6:S2/S1, EP12:S2/S1 and one in 3A isolate EP9:S2/Sl. Point mutations were found in strains EP3, EP6, EP9 and EP12. Recombination specific types and sites re-occurrence along with point mutations are discussed concerning the polioviruses evolution

Correlation of mutations and recombination with growth kinetics of poliovirus vaccine strains

Attenuated strains of Sabin poliovirus vaccine replicate in the human gut and, in rare cases, may cause vaccine-associated paralytic poliomyelitis (VAPP). The genetic instability of Sabin strains constitutes one of the main causes of VAPP, a disease that is most frequently associated with type 3 and type 2 Sabin strains, and more rarely with type 1 Sabin strains. In the present study, the growth phenotype of eight oral poliovirus vaccine (OPV) isolates (two non-recombinants and six recombinants), as well as of Sabin vaccine strains, was evaluated using two different assays, the reproductive capacity at different temperatures (Rct) test and the one-step growth curve test in Hep-2 cells at two different temperatures (37A degrees C and 40A degrees C). The growth phenotype of isolates was correlated with genomic modifications in order to identify the determinants and mechanisms of reversion towards neurovirulence. All of the recombinant OPV isolates showed a thermoresistant phenotype in the Rct test. Moreover, both recombinant Sabin-3 isolates showed significantly higher viral yield than Sabin 3 vaccine strain at 37A degrees C and 40A degrees C in the one-step growth curve test. All of the OPV isolates displayed mutations at specific sites of the viral genome, which are associated with the attenuated and temperature-sensitive phenotype of Sabin strains. The results showed that both mutations and recombination events could affect the phenotype traits of Sabin derivatives and may lead to the reversion of vaccinal strains to neurovirulent ones. The use of phenotypic markers along with the genomic analysis may shed additional light on the molecular determinants of the reversed neurovirulent phenotype of Sabin derivatives