[A Pair of Siblings with Frontotemporal Dementia and Amyotrophic Lateral Sclerosis and a Novel Thr462Lysfs Mutation in the TBK1 Gene]. / Ein Geschwisterpaar mit frontotemporaler Lobärdegeneration und amyotropher Lateralsklerose und einer neuen Mutation im TBK1-Gen (Thr462Lysfs).

We report on a pair of siblings with frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) and a novel Thr462Lysfs mutation in the TANK-binding kinase 1 (TBK1) gene identified through the European Early-Onset Dementia Consortium. The patients presented at the age of 77 and 75 years and displayed dementia and bulbar symptoms as well as progressive paresis. After a progressive course, both of them died only a few months after diagnosis. Most recently, TBK1 mutations were identified in patients with FTD and ALS. A loss of expression of the mutant allele, leading to 50 % reduced TBK1 protein levels, seems to be causative. The occurrence of TBK1 mutations in FTD and ALS underlines the fact that FTD and ALS are part of the same disease spectrum. For future therapeutic trials, characterization of TBK1 mutation carriers in presymptomatic cohorts, such as the genetic frontotemporal dementia initiative (GENFI), is of great importance.

The C9orf72 repeat size correlates with onset age of disease, DNA methylation and transcriptional downregulation of the promoter.

Pathological expansion of a G4C2 repeat, located in the 5' regulatory region of C9orf72, is the most common genetic cause of frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). C9orf72 patients have highly variable onset ages suggesting the presence of modifying factors and/or anticipation. We studied 72 Belgian index patients with FTLD, FTLD-ALS or ALS and 61 relatives with a C9orf72 repeat expansion. We assessed the effect of G4C2 expansion size on onset age, the role of anticipation and the effect of repeat size on methylation and C9orf72 promoter activity. G4C2 expansion sizes varied in blood between 45 and over 2100 repeat units with short expansions (45-78 units) present in 5.6% of 72 index patients with an expansion. Short expansions co-segregated with disease in two families. The subject with a short expansion in blood but an indication of mosaicism in brain showed the same pathology as those with a long expansion. Further, we provided evidence for an association of G4C2 expansion size with onset age (P<0.05) most likely explained by an association of methylation state of the 5' flanking CpG island and expansion size in blood (P<0.0001) and brain (P<0.05). In several informative C9orf72 parent-child transmissions, we identified earlier onset ages, increasing expansion sizes and/or increasing methylation states (P=0.0034) of the 5' CpG island, reminiscent of disease anticipation. Also, intermediate repeats (7-24 units) showed a slightly higher methylation degree (P<0.0001) and a decrease of C9orf72 promoter activity (P<0.0001) compared with normal short repeats (2-6 units). Decrease of transcriptional activity was even more prominent in the presence of small deletions flanking G4C2 (P<0.0001). Here we showed that increased methylation of CpGs in the C9orf72 promoter may explain how an increasing G4C2 size lead to loss-of-function without excluding repeat length-dependent toxic gain-of-function. These data provide insights into disease mechanisms and have important implications for diagnostic counseling and potential therapeutic approaches.

Increased expression of BIN1 mediates Alzheimer genetic risk by modulating tau pathology.

Genome-wide association studies (GWAS) have identified a region upstream the BIN1 gene as the most important genetic susceptibility locus in Alzheimer's disease (AD) after APOE. We report that BIN1 transcript levels were increased in AD brains and identified a novel 3 bp insertion allele ∼28 kb upstream of BIN1, which increased (i) transcriptional activity in vitro, (ii) BIN1 expression levels in human brain and (iii) AD risk in three independent case-control cohorts (Meta-analysed Odds ratio of 1.20 (1.14-1.26) (P=3.8 × 10(-11))). Interestingly, decreased expression of the Drosophila BIN1 ortholog Amph suppressed Tau-mediated neurotoxicity in three different assays. Accordingly, Tau and BIN1 colocalized and interacted in human neuroblastoma cells and in mouse brain. Finally, the 3 bp insertion was associated with Tau but not Amyloid loads in AD brains. We propose that BIN1 mediates AD risk by modulating Tau pathology.

Alzheimer risk associated with a copy number variation in the complement receptor 1 increasing C3b/C4b binding sites.

Two multicentre genome-wide association (GWA) studies provided substantial evidence, implicating the complement receptor 1 gene (CR1) in Alzheimer disease (AD) genetic etiology. CR1 encodes a large transmembrane receptor with a crucial role in the immune complement cascade. We performed a genetic follow-up of the GWA CR1 association in a Flanders-Belgian cohort (n=1883), and investigated the effect of single-nucleotide polymorphisms (SNPs) located in the CR1 locus on AD risk and cerebrospinal fluid (CSF) biomarker levels. We obtained significant association (P(adj)<0.03; odds ratio (OR)=1.24 (95% confidence interval (CI): 1.02-1.51)) for one CR1 risk haplotype, and haplotype association was strongest in individuals carrying apolipoprotein E (APOE) ɛ4 alleles (P(adj)<0.006; OR=1.50 (95% CI: 1.08-2.09)). Also, four SNPs correlated with increased CSF amyloid Aß1₋42 levels, suggesting a role for the CR1 protein in Aß metabolism. Moreover, we quantified a low-copy repeat (LCR)-associated copy number variation (CNV) in CR1, producing different CR1 isoforms, CR1-F and CR1-S, and obtained significant association in carriers of CR1-S. We replicated the CR1 CNV association finding in a French cohort (n=2003) and calculated in the combined cohorts, an OR of 1.32; 95% CI: 1.10-1.59 (P=0.0025). Our data showed that the common AD risk association may well be explained by the presence of CR1-S increasing the number of C3b/C4b and cofactor activity sites and AD risk with 30% in CR1-S carriers. How precisely the different functional role of CR1-S in the immune complement cascade contributes to AD pathogenesis will need additional functional studies.

APOE and Alzheimer disease: a major gene with semi-dominant inheritance.

Apolipoprotein E (APOE) dependent lifetime risks (LTRs) for Alzheimer Disease (AD) are currently not accurately known and odds ratios alone are insufficient to assess these risks. We calculated AD LTR in 7351 cases and 10 132 controls from Caucasian ancestry using Rochester (USA) incidence data. At the age of 85 the LTR of AD without reference to APOE genotype was 11% in males and 14% in females. At the same age, this risk ranged from 51% for APOE44 male carriers to 60% for APOE44 female carriers, and from 23% for APOE34 male carriers to 30% for APOE34 female carriers, consistent with semi-dominant inheritance of a moderately penetrant gene. Using PAQUID (France) incidence data, estimates were globally similar except that at age 85 the LTRs reached 68 and 35% for APOE 44 and APOE 34 female carriers, respectively. These risks are more similar to those of major genes in Mendelian diseases, such as BRCA1 in breast cancer, than those of low-risk common alleles identified by recent GWAS in complex diseases. In addition, stratification of our data by age groups clearly demonstrates that APOE4 is a risk factor not only for late-onset but for early-onset AD as well. Together, these results urge a reappraisal of the impact of APOE in Alzheimer disease.

EFNS guidelines for the molecular diagnosis of neurogenetic disorders: motoneuron, peripheral nerve and muscle disorders.

OBJECTIVES: These EFNS guidelines on the molecular diagnosis of motoneuron disorders, neuropathies and myopathies are designed to summarize the possibilities and limitations of molecular genetic techniques and to provide diagnostic criteria for deciding when a molecular diagnostic work-up is indicated. SEARCH STRATEGY: To collect data about planning, conditions and performance of molecular diagnosis of these disorders, a literature search in various electronic databases was carried out and original papers, meta-analyses, review papers and guideline recommendations reviewed. RESULTS: The best level of evidence for genetic testing recommendation (B) can be found for the disorders with specific presentations, including familial amyotrophic lateral sclerosis, spinal and bulbar muscular atrophy, Charcot-Marie-Tooth 1A, myotonic dystrophy and Duchenne muscular dystrophy. For a number of less common disorders, a precise description of the phenotype, including the use of immunologic methods in the case of myopathies, is considered as good clinical practice to guide molecular genetic testing. CONCLUSION: These guidelines are provisional and the future availability of molecular-genetic epidemiological data about the neurogenetic disorders under discussion in this article will allow improved recommendation with an increased level of evidence.

EFNS guidelines on the molecular diagnosis of channelopathies, epilepsies, migraine, stroke, and dementias.

OBJECTIVES: These EFNS guidelines on the molecular diagnosis of channelopathies, including epilepsy and migraine, as well as stroke, and dementia are designed to summarize the possibilities and limitations of molecular genetic techniques and to provide diagnostic criteria for deciding when a molecular diagnostic work-up is indicated. SEARCH STRATEGY: To collect data about planning, conditions, and performance of molecular diagnosis of these disorders, a literature search in various electronic databases was carried out and original papers, meta-analyses, review papers, and guideline recommendations were reviewed. RESULTS: The best level of evidence for genetic testing recommendation (B) can be found for a small number of syndromes, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, severe myoclonic epilepsy of infancy, familial recurrent hemorrhages, familial Alzheimer's disease, and frontotemporal lobar degeneration. Good practice points can be formulated for a number of other disorders. CONCLUSION: These guidelines are provisional, and the future availability of molecular genetic epidemiological data about the neurogenetic disorders under discussion in our article will allow improved recommendation with an increased level of evidence.

Genetic contribution of FUS to frontotemporal lobar degeneration.

BACKGROUND: Recently, the FUS gene was identified as a new causal gene for amyotrophic lateral sclerosis (ALS) in approximately 4% of patients with familial ALS. Since ALS and frontotemporal lobar degeneration (FTLD) are part of a clinical, pathologic, and genetic disease spectrum, we investigated a potential role of FUS in FTLD. METHODS: We performed mutational analysis of FUS in 122 patients with FTLD and 15 patients with FTLD-ALS, as well as in 47 patients with ALS. Mutation screening was performed by sequencing of PCR amplicons of the 15 FUS exons. RESULTS: We identified 1 patient with FTLD with a novel missense mutation, M254V, that was absent in 638 control individuals. In silico analysis predicted this amino acid substitution to be pathogenic. The patient did not have a proven family history of neurodegenerative brain disease. Further, we observed the known R521H mutation in 1 patient with ALS. No FUS mutations were detected in the patients with FTLD-ALS. While insertions/deletions of 2 glycines (G) were suggested to be pathogenic in the initial FUS reports, we observed an identical GG-deletion in 2 healthy individuals and similar G-insertions/deletions in 4 other control individuals, suggesting that G-insertions/deletions within this G-rich region may be tolerated. CONCLUSIONS: In a first analysis of FUS in patients with frontotemporal lobar degeneration (FTLD), we identified a novel FUS missense mutation, M254V, in 1 patient with pure FTLD. At this point, the biologic relevance of this mutation remains elusive. Screening of additional FTLD patient cohorts will be needed to further elucidate the contribution of FUS mutations to FTLD pathogenesis.

EFNS guidelines on the molecular diagnosis of ataxias and spastic paraplegias.

BACKGROUND AND PURPOSE: These EFNS guidelines on the molecular diagnosis of neurogenetic disorders are designed to provide practical help for the general neurologist to make appropriate use of molecular genetics in diagnosing neurogenetic disorders. METHODS: Literature searches were performed before expert members of the task force wrote proposals, which were discussed in detail until final consensus had been reached among all task force members. RESULTS AND CONCLUSION: This paper provides updated guidelines for molecular diagnosis of two particularly complex groups of disorders, the ataxias and spastic paraplegias. Possibilities and limitations of molecular genetic diagnosis of these disorders are evaluated and recommendations are provided.

EFNS guidelines on the molecular diagnosis of mitochondrial disorders.

OBJECTIVES: These European Federation of Neurological Sciences (EFNS) guidelines are designed to provide practical help for the general neurologist to make appropriate use of molecular genetics for diagnosing mitochondrial disorders (MIDs), which gain increasing attention and are more frequently diagnosed due to improved diagnostic tools. BACKGROUND: Since the publication of the first EFNS guidelines on the molecular diagnosis of inherited neurological diseases in 2001, rapid progress has been made in this field, necessitating the creation of an updated version. SEARCH STRATEGY: To collect data about the molecular diagnosis of MIDs search for literature in various electronic databases, such as Cochrane library, MEDLINE, OMIM, GENETEST or Embase, were carried out and original papers, meta-analyses, review papers, and guideline recommendations were reviewed. RESULTS: The guidelines summarise the possibilities and limitations of molecular genetic diagnosis of MIDs and provide practical recommendations and diagnostic criteria in accordance with the EFNS Scientific Committee to guide the molecular diagnostic work-up of MIDs. RECOMMENDATIONS: The proposed guidelines suggest an approach to the molecular diagnosis of MIDs in a manner accessible to general neurologists.

Novel Twinkle gene mutation in autosomal dominant progressive external ophthalmoplegia and multisystem failure.

A Saudi Arabian family presented with adult onset autosomal dominant progressive external ophthalmoplegia (adPEO) complicated by late onset reversible failure of the CNS, respiratory, hepatic, and endocrine systems. Clinical findings were suggestive of mitochondrial dysfunction and multiple mitochondrial DNA deletions were demonstrated on long range and real time polymerase chain reaction assays but not on Southern blotting. The disorder is caused by a novel heterozygous PEO1 mutation predicting a Leu360Gly substitution in the twinkle protein. The peculiar clinical presentation expands the variable phenotype observed in adPEO and Twinkle gene mutations.

Clinical heterogeneity in 3 unrelated families linked to VCP p.Arg159His.

BACKGROUND: Families associated with missense mutations in the valosin-containing protein (VCP) present with a rare autosomal dominant multisystem disorder of frontotemporal lobar degeneration (FTLD), inclusion body myopathy (IBM), and Paget disease of bone (PDB), referred to as IBMPFD. METHODS: We used exon-based genomic DNA sequencing to test for VCP mutations in 123 unrelated Belgian patients with FTLD and their relatives, and the absence of such mutations in 157 control individuals. We analyzed haplotype sharing among mutation carriers by genotyping 8 microsatellite markers in the VCP locus. We obtained family history and clinical and pathologic data using established diagnostic instruments. RESULTS: Mutation analysis of VCP identified 2 Belgian patients with FTLD carrying the p.Arg159His mutation, which segregated in their families. In one family, patients presented with FTLD only, whereas in the other family, patients developed FTLD, PDB, or both without signs of IBM for any of the mutation carriers. We had previously identified p.Arg159His in an Austrian family with patients exhibiting both IBM and PDB. Haplotype sharing analysis indicated that the 3 p.Arg159His families are unrelated. Clinical follow-up of the Austrian family identified dementia symptoms in 1 patient. Autopsy data of 3 patients of the 2 Belgian families revealed FTLD pathology with numerous ubiquitin-immunoreactive, intranuclear inclusions and dystrophic neurites staining positive for TDP-43 protein. CONCLUSIONS: In 3 unrelated families with IBMPFD segregating VCP p.Arg159His, we observed a high degree of clinical heterogeneity and variable penetrance of the 3 cardinal clinical phenotypes: inclusion body myopathy, Paget disease of bone, and frontotemporal lobar degeneration. In contrast, the neuropathologic phenotype was consistent with FTLD-TDP type 4.

EFNS guidelines on the molecular diagnosis of neurogenetic disorders: general issues, Huntington's disease, Parkinson's disease and dystonias.

BACKGROUND AND PURPOSE: These EFNS guidelines on the molecular diagnosis of neurogenetic disorders are designed to provide practical help for the general neurologist to make appropriate use of molecular genetics in diagnosing neurogenetic disorders. Since the publication of the first two EFNS-guideline papers on the molecular diagnosis of neurological diseases in 2001, rapid progress has been made in this field, necessitating an updated series of guidelines. METHODS: Literature searches were performed before expert members of the task force wrote proposals, which were discussed in detail until final consensus had been reached among all task force members. RESULTS AND CONCLUSION: This paper provides updated guidelines for molecular diagnosis of Huntington's disease, Parkinson's disease and dystonias as well as a general introduction to the topic. Possibilities and limitations of molecular genetic diagnosis of these disorders are evaluated and recommendations are provided.

Fabry disease in a patient with Turner syndrome.

We report a unique case with co-occurrence of Turner syndrome and Fabry disease (OMIM #301500). The latter is a rare X-linked lysosomal storage disease that is characterized by partial or complete deficiency of alpha-galactosidase A (GLA; EC 3.2.1.22) following mutations in the gene (GLA) localized at Xq22.1. Accumulation of metabolic intermediates can occur in many tissues and leads to severe morbidity, especially due to renal failure, cardiac involvement and stroke. It is well established that hemizygous male mutation carriers with Fabry disease are generally more severely affected than heterozygous female mutation carriers, but disabling clinical features and disease progression often occur in female Fabry patients as well. The majority of this patient's cells are of the 45,X type, making her a hemizygous GLA mutation carrier displaying a very severe Fabry disease phenotype.

Progranulin variability has no major role in Parkinson disease genetic etiology.

BACKGROUND: Different loss-of-function mutations were identified underlying PGRN haploinsufficiency in patients with frontotemporal lobar degeneration. PGRN mutations were also identified in other neurodegenerative brain diseases such as amyotrophic lateral sclerosis and Alzheimer disease, though their biologic contribution to these diseases remains elusive. Because of its apparent role in neuronal survival, we argued that PGRN might also contribute to Parkinson disease (PD) pathogenesis. METHODS: We screened PGRN exons for mutations in 255 patients with PD and 459 control individuals by direct genomic sequencing. Genetic association of PGRN with risk for PD was assessed using single nucleotide polymorphisms (SNPs) across the gene. RESULTS: In patients we identified four missense mutations of which p.Asp33Glu and p.Arg514Met were absent in control individuals. Single SNP and haplotype analyses did not detect significant associations with PD. CONCLUSIONS: Our results do not support a major role for PGRN in the genetic etiology of Parkinson disease (PD). At this stage and in the absence of functional data, it remains unclear whether p.Asp33Glu and p.Arg514Met are biologically relevant to PD pathogenesis in the mutation carriers.

The association between APOE genotype and memory dysfunction in subjects with mild cognitive impairment is related to age and Alzheimer pathology.

BACKGROUND: Memory problems are a main feature of mild cognitive impairment (MCI) and may be related to the apolipoprotein E (APOE) epsilon4 allele. We investigated whether the effect of the APOE genotype on memory in subjects with MCI was dependent on age and underlying Alzheimer disease (AD) pathology. METHODS: Subjects with MCI (n = 180) were selected from a memory clinic setting. Subjects with at least one APOE epsilon4 allele (n = 83) were compared to non-carriers on several memory measures. Subjects were reassessed 5-10 years later in order to identify those who developed AD. RESULTS: In the middle-aged subgroup, the APOE epsilon4 allele was most strongly related to decreased subjective organization and in the old subgroup to a decreased delayed recall. After excluding subjects with incipient AD (n = 33), results remained similar in the middle-aged subgroup, but in the old subgroup the APOE genotype was no longer associated with memory dysfunction. CONCLUSION: The presence of the APOE epsilon4 allele is associated with impaired memory functioning in both middle-aged and old subjects with MCI, although the memory function affected varies with age. Its effect on memory function may be dependent on underlying AD pathology in elderly subjects, but not in middle-aged subjects.

Granulin mutations associated with frontotemporal lobar degeneration and related disorders: an update.

Mutations in the gene encoding granulin (HUGO gene symbol GRN, also referred to as progranulin, PGRN), located at chromosome 17q21, were recently linked to tau-negative ubiquitin-positive frontotemporal lobar degeneration (FTLDU). Since then, 63 heterozygous mutations were identified in 163 families worldwide, all leading to loss of functional GRN, implicating a haploinsufficiency mechanism. Together, these mutations explained 5 to 10% of FTLD. The high mutation frequency, however, might still be an underestimation because not all patient samples were examined for all types of loss-of-function mutations and because several variants, including missense mutations, have a yet uncertain pathogenic significance. Although the complete phenotypic spectrum associated with GRN mutations is not yet fully characterized, it was shown that it is highly heterogeneous, suggesting the influence of modifying factors. A role of GRN in neuronal survival was suggested but the exact mechanism by which neurodegeneration and deposition of pathologic brain inclusions occur still has to be clarified.

Genetic variability in progranulin contributes to risk for clinically diagnosed Alzheimer disease.

OBJECTIVE: Loss-of-function mutations in the progranulin gene (PGRN) were identified in frontotemporal lobar degeneration (FTLD) with ubiquitin-immunoreactive neuronal inclusions (FTLD-U). We assessed whether PGRN also contributes to genetic risk for Alzheimer disease (AD) in an extended Belgian AD patient group (n = 779, onset age 74.7 +/- 8.7 years). METHODS: A mutation analysis of the PGRN coding region was performed. The effect of missense mutations was assessed using in silico predictions and protein modeling. Risk effects of common genetic variants were estimated by logistic regression analysis and gene-based haplotype association analysis. RESULTS: We observed seven missense mutations in eight patients (1.3%). Convincing pathogenic evidence was obtained for two missense mutations, p.Cys139Arg and p.Pro451Leu, affecting PGRN protein folding and leading to loss of PGRN by degradation of the misfolded protein. In addition, we showed that PGRN haplotypes were associated with increased risk for AD. CONCLUSIONS: Our data support a role for PGRN in patients with clinically diagnosed Alzheimer disease (AD). Further, we hypothesize that at least some PGRN missense mutations might lead to loss of functional protein. Whether the underlying pathology in our cases proves to be AD, frontotemporal lobar degeneration, or a combination of the two must await further investigations.