Recent origin and spread of a common Welsh MAPT splice mutation causing frontotemporal lobar degeneration

Searching for Grendel: origin and global spread of the C9ORF72 repeat expansion

Recent advances are uncovering more and more of the genetic architecture underlying amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative condition that affects ~6,000 Americans annually. Chief among these was the discovery that a large repeat expansion in the C9ORF72 gene is responsible for an unprecedented portion of familial and sporadic ALS cases. Much has been published on how this expansion disrupts neuronal homeostasis and how gene-based therapy might be an effective treatment in the future. Nevertheless, it is instructive to look back at the origins of this important mutation. In this opinion piece, we attempt to answer three key questions concerning C9ORF72. First, how many times did the expansion occur throughout human history? Second, how old is the expansion? And finally and perhaps most importantly, how did the expansion spread throughout Europe? We speculate that the expansion occurred only once in the past, that this event took place in the Finnish population and that the Vikings and their descendants were responsible for disseminating this mutation throughout the rest of the continent.

Familial Lund frontotemporal dementia caused by C9ORF72 hexanucleotide expansion

Frontotemporal dementia (FTD) as an important clinical entity was rediscovered in Lund and Manchester in the early 1990s. Here we show that the large Lund pedigree with behavioral variant of frontotemporal dementia previously described with this disorder has an expansion in the recently described C9ORF72 locus on chromosome 9.

PSF suppresses tau exon 10 inclusion by interacting with a stem-loop structure downstream of exon 10

Microtubule binding protein Tau has been implicated in a wide range of neurodegenerative disorders collectively classified as tauopathies. Exon 10 of the human tau gene, which codes for a microtubule binding repeat region, is alternatively spliced to form Tau protein isoforms containing either four or three microtubule binding repeats, Tau4R and Tau3R, respectively. The levels of different Tau splicing isoforms are fine-tuned by alternative splicing with the ratio of Tau4R/Tau3R maintained approximately at one in adult neurons. Mutations that disrupt tau exon 10 splicing regulation cause an imbalance of different tau splicing isoforms and have been associated with tauopathy. To search for factors interacting with tau pre-messenger RNA (pre-mRNA) and regulating tau exon 10 alternative splicing, we performed a yeast RNA-protein interaction screen and identified polypyrimidine tract binding protein associated splicing factor (PSF) as a candidate tau exon 10 splicing regulator. UV crosslinking experiments show that PSF binds to the stem-loop structure at the 5' splice site downstream of tau exon 10. This PSF-interacting RNA element is distinct from known PSF binding sites previously identified in other genes. Overexpression of PSF promotes tau exon 10 exclusion, whereas down-regulation of the endogenous PSF facilitates exon 10 inclusion. Immunostaining shows that PSF is expressed in the human brain regions affected by tauopathy. Our data reveal a new player in tau exon 10 alternative splicing regulation and uncover a previously unknown mechanism of PSF in regulating tau pre-mRNA splicing.

Founder effect and estimation of the age of the Progranulin Thr272fs mutation in 14 Italian pedigrees with frontotemporal lobar degeneration

Progranulin (PGRN) mutations have been recognized to be monogenic causes of frontotemporal lobar degeneration (FTLD). PGRN Thr272fs mutation in the Italian population has been previously identified. In the present study, we evaluated the occurrence of a founder effect studying 8 polymorphic microsatellite markers flanking the PGRN gene in 14 apparently unrelated families. We identified a common haplotype associated with PGRN Thr272fs carriers, assuming common ancestry. The inferred age analysis (range between 260 [95% credible set: 227-374] and 295 [95% credible set: 205-397] generations) places the introduction of the mutation back to the Neolithic era when the Celts, the population of that period, settled in Northern Italy. PGRN Thr272fs mutation appears to be as either behavioral frontotemporal dementia (80%) or primary progressive aphasia (20%), it was equally distributed between male and female, and the mean age at onset was 59.6 ± 5.9 (range 53-68). In 14 families, autosomal dominant pattern of inheritance was present in 64.2% of cases. No clinical predictors of disease onset were demonstrated. The identification of a large cohort of frontotemporal lobar degeneration (FTLD) patients with homogeneous genetic background well may be used in the search of disease modulators to elucidate genotype-phenotype correlations of progranulopathies.