Background-Recent studies indicate an increased frequency of mutations in the gene for Gaucher disease, glucocerebrosidase (GBA), among patients with Parkinson disease. An international collaborative study was conducted to ascertain the frequency of GBA mutations in ethnically diverse patients with Parkinson disease.

DNA methyltransferase (cytosine-5) 1 (Dnmt1) is the principal enzyme responsible for maintenance of CpG methylation and is essential for the regulation of gene expression, silencing of parasitic DNA elements, genomic imprinting and embryogenesis. Dnmt1 is needed in S phase to methylate newly replicated CpGs occurring opposite methylated ones on the mother strand of the DNA, which is essential for the epigenetic inheritance of methylation patterns in the genome. Despite an intrinsic affinity of Dnmt1 for such hemi-methylated DNA, the molecular mechanisms that ensure the correct loading of Dnmt1 onto newly replicated DNA in vivo are not understood. The Np95 (also known as Uhrf1 and ICBP90) protein binds methylated CpG through its SET and RING finger-associated (SRA) domain. Here we show that localization of mouse Np95 to replicating heterochromatin is dependent on the presence of hemi-methylated DNA. Np95 forms complexes with Dnmt1 and mediates the loading of Dnmt1 to replicating heterochromatic regions. By using Np95-deficient embryonic stem cells and embryos, we show that Np95 is essential in vivo to maintain global and local DNA methylation and to repress transcription of retrotransposons and imprinted genes. The link between hemi-methylated DNA, Np95 and Dnmt1 thus establishes key steps of the mechanism for epigenetic inheritance of DNA methylation.

SummaryBackgroundWe aimed to accurately estimate the frequency of a hexanucleotide repeat expansion in C9orf72 that has been associated with a large proportion of cases of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD).MethodsWe screened 4448 patients diagnosed with ALS (El Escorial criteria) and 1425 patients with FTD (Lund-Manchester criteria) from 17 regions worldwide for the GGGGCC hexanucleotide expansion using a repeat-primed PCR assay. We assessed familial disease status on the basis of self-reported family history of similar neurodegenerative diseases at the time of sample collection. We compared haplotype data for 262 patients carrying the expansion with the known Finnish founder risk haplotype across the chromosomal locus. We calculated age-related penetrance using the Kaplan-Meier method with data for 603 individuals with the expansion.FindingsIn patients with sporadic ALS, we identified the repeat expansion in 236 (7·0%) of 3377 white individuals from the USA, Europe, and Australia, two (4·1%) of 49 black individuals from the USA, and six (8·3%) of 72 Hispanic individuals from the USA. The mutation was present in 217 (39·3%) of 552 white individuals with familial ALS from Europe and the USA. 59 (6·0%) of 981 white Europeans with sporadic FTD had the mutation, as did 99 (24·8%) of 400 white Europeans with familial FTD. Data for other ethnic groups were sparse, but we identified one Asian patient with familial ALS (from 20 assessed) and two with familial FTD (from three assessed) who carried the mutation. The mutation was not carried by the three Native Americans or 360 patients from Asia or the Pacific Islands with sporadic ALS who were tested, or by 41 Asian patients with sporadic FTD. All patients with the repeat expansion had (partly or fully) the founder haplotype, suggesting a one-off expansion occurring about 1500 years ago. The pathogenic expansion was non-penetrant in individuals younger than 35 years, 50% penetrant by 58 years, and almost fully penetrant by 80 years.InterpretationA common Mendelian genetic lesion in C9orf72 is implicated in many cases of sporadic and familial ALS and FTD. Testing for this pathogenic expansion should be considered in the management and genetic counselling of patients with these fatal neurodegenerative diseases.FundingFull funding sources listed at end of paper (see Acknowledgments).

Expanded polyglutamine repeats have been proposed to cause neuronal degeneration in Huntington's disease (HD) and related disorders, through abnormal interactions with other proteins containing short polyglutamine tracts such as the transcriptional coactivator CREB binding protein, CBP. We found that CBP was depleted from its normal nuclear location and was present in polyglutamine aggregates in HD cell culture models, HD transgenic mice, and human HD postmortem brain. Expanded polyglutamine repeats specifically interfere with CBP-activated gene transcription, and overexpression of CBP rescued polyglutamine-induced neuronal toxicity. Thus, polyglutamine-mediated interference with CBP-regulated gene transcription may constitute a genetic gain of function, underlying the pathogenesis of polyglutamine disorders.

There is no proof that the HN cDNA represents a gene, that its origin is nuclear, or that the HN peptide is produced in vivo. The information that the long HN cDNA sequence is virtually identical to mitochondrial rRNA should have been put in the Discussion rather than published as supplementary material. The Discussion should have contained the following:The long cDNA [1,567 bp including a poly(A) tail] containing the HN ORF is Ͼ99% identical (1548͞1552) to positions 1679-3230 of mitochondrial DNA (GenBank accession no. AB055387). Because mitochondrial DNA positions 1667-3224 code for mitochondrial 16S rRNA, and mitochondrial 16S rRNA has a short poly(A) tail during transcription (1), the virtual identity of the long HN cDNA to mitochondrial DNA indicates that HN cDNA is mitochondrial 16S rRNA with a poly(A) tail. This makes it unlikely that the peptide encoded by the ORF in HN cDNA is naturally produced. Further, the 75-bp HN ORF is separated from the 5Ј end of the long HN cDNA by a 950-bp region containing at least seven ORFs, each with a stop codon. This makes it even more unlikely that HN peptide is produced from the long HN cDNA. It should also be noted that mitochondria-like nuclear sequences occur commonly as pseudogenes (2). Finally, the HN peptide lacks the characteristic N-terminal signal sequence of secreted peptides, although we suggest that a signal peptide-like function may be encoded in the primary sequence of HN peptide. For all of these reasons, it is unlikely that the HN ORF leads to production of the predicted peptide in vivo.Nonetheless, it remains possible that HN cDNA represents a nuclear transcribed mRNA and that the HN peptide is a natural product. Long regions of the HN cDNA are Ͼ99% identical to certain registered human mRNAs [1545͞1553 at positions 14-1580 of FLJ22981 fis cDNA (AK026634), 925͞929 at positions 1-929 of FLJ22517 fis cDNA, 914͞919 at positions 1348-2266 of FLJ20341 fis cDNA, and 345͞346 at positions 1-346 of PNAS-32 mRNA]. PNAS-32 mRNA is actually expressed to produce NB4 apoptosis-related protein, showing that this mRNA is transcribed from a nuclear gene. In addition, HN cDNA is highly similar to regions of more than 1,000 bp on human chromosomes [positions 245364-244075 of chromosome 11 draft sequence (92%, 1198͞1290), positions 65752-66775 of chromosome X draft sequence (95%, 974͞1025), and positions 687598-688608 of chromosome 5 draft sequence (93%, 954͞1016)]. Also, the HN ORF has a Kozak-like sequence, although it is not canonical.