A. Volk

Haploinsufficiency of TBK1 causes familial ALS and fronto-temporal dementia

Amyotrophic lateral sclerosis (ALS) is a genetically heterogeneous neurodegenerative syndrome hallmarked by adult-onset loss of motor neurons. We performed exome sequencing of 252 familial ALS (fALS) and 827 control individuals. Gene-based rare variant analysis identified an exome-wide significant enrichment of eight loss-of-function (LoF) mutations in TBK1 (encoding TANK-binding kinase 1) in 13 fALS pedigrees. No enrichment of LoF mutations was observed in a targeted mutation screen of 1,010 sporadic ALS and 650 additional control individuals. Linkage analysis in four families gave an aggregate LOD score of 4.6. In vitro experiments confirmed the loss of expression of TBK1 LoF mutant alleles, or loss of interaction of the C-terminal TBK1 coiled-coil domain (CCD2) mutants with the TBK1 adaptor protein optineurin, which has been shown to be involved in ALS pathogenesis. We conclude that haploinsufficiency of TBK1 causes ALS and fronto-temporal dementia.

Neurofilaments in the diagnosis of motoneuron diseases: a prospective study on 455 patients

Objectives Biomarkers for the diagnosis of motoneuron diseases (MND) are urgently needed to improve the diagnostic pathway, patient stratification and monitoring. The aim of this study was to validate candidate markers for MND in cerebrospinal fluid (CSF) and specify cut-offs based on large patient cohorts by especially considering patients who were seen under the initial differential diagnosis (MND mimics). Methods In a prospective study, we investigated CSF of 455 patients for neurofilament light chain (NfL), phosphorylated heavy chain (pNfH), tau protein (Tau) and phospho-tau protein (pTau). Analysed cohorts included patients with apparently sporadic and familial amyotrophic lateral sclerosis (ALS) and primary lateral sclerosis (PLS) (MND, n=253), MND mimics (n=85) and neurological control groups. Cut-off values were specified, and diagnostic performance and correlation with progression were analysed. Results Nfs were significantly higher in the MND group compared to the control groups, whereas Tau and pTau did not differ. At a cut-off level of 2200 pg/mL for NfL, a 77% diagnostic sensitivity (CI 71% to 82%), 85% specificity (CI 79% to 90%) and 87% positive predictive value (PPV) (CI 81% to 91%) were achieved. For pNfH, we calculated 83% sensitivity (CI 78% to 88%), 77% specificity (CI 71% to 83%) and 82% PPV (CI 77% to 86%) at 560 pg/mL. There were no significant differences between sporadic and genetic ALS or PLS. Nf levels were elevated at early disease stage, and correlated moderately with MND progression and duration. Conclusions Neurofilaments in CSF have a high relevance for the differential diagnosis of MNDs and should be included in the diagnostic work-up of patients. Their value as prognostic markers should be investigated further.

A blinded international study on the reliability of genetic testing for GGGGCC-repeat expansions in C9orf72 reveals marked differences in results among 14 laboratories

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.

Neurofilament levels as biomarkers in asymptomatic and symptomatic familial amyotrophic lateral sclerosis.

Neurofilaments are elevated in the cerebrospinal fluid (CSF) and serum of amyotrophic lateral sclerosis (ALS) patients. However, timing of this increase is unknown. To characterize the premanifest disease phase, we performed a cross‐sectional study on asymptomatic (n = 12) and symptomatic (n = 64) ALS mutation carriers and family controls (n = 19). Neurofilaments NF‐L (neurofilament–light chain) and pNF‐H (phosphorylated neurofilament–heavy chain) are normal before symptom onset and increased by at least an order of magnitude at early symptom onset in CSF (pNF‐H) or serum and CSF (NF‐L). Thus, blood and CSF neurofilament levels are linked to the symptomatic phase of ALS and might serve as objective markers of structural damage to the nervous system. ANN NEUROL 2016;79:152–158

Neurofilaments levels as biomarkers in asymptomatic and symptomatic familial ALS

Neurofilaments are elevated in the cerebrospinal fluid (CSF) and serum of amyotrophic lateral sclerosis (ALS) patients. However, timing of this increase is unknown. To characterize the premanifest disease phase, we performed a cross‐sectional study on asymptomatic (n = 12) and symptomatic (n = 64) ALS mutation carriers and family controls (n = 19). Neurofilaments NF‐L (neurofilament–light chain) and pNF‐H (phosphorylated neurofilament–heavy chain) are normal before symptom onset and increased by at least an order of magnitude at early symptom onset in CSF (pNF‐H) or serum and CSF (NF‐L). Thus, blood and CSF neurofilament levels are linked to the symptomatic phase of ALS and might serve as objective markers of structural damage to the nervous system. ANN NEUROL 2016;79:152–158

Reply: Two novel mutations in conserved codons indicate that CHCHD10 is a gene associated with motor neuron disease

Sylvie Bannwarth, Samira Ait-El-Mkadem, Annabelle Chaussenot, Emmanuelle C. Genin, Sandra Lacas-Gervais, Konstantina Fragaki, Laetitia Berg-Alonso, Yusuke Kageyama, Valérie Serre, David Moore, Annie Verschueren, Cécile Rouzier, Isabelle Le Ber, Gaëlle Augé, Charlotte Cochaud, Françoise Lespinasse, Karine N’Guyen, Anne de Septenville, Alexis Brice, Patrick Yu-Wai-Man, Hiromi Sesaki, Jean Pouget and Véronique Paquis-Flucklinger

C9ORF72 Repeat Expansion in Australian and Spanish Frontotemporal Dementia Patients

A hexanucleotide repeat expansion in C9ORF72 has been established as a common cause of frontotemporal dementia (FTD). However, the minimum repeat number necessary for disease pathogenesis is not known. The aims of our study were to determine the frequency of the C9ORF72 repeat expansion in two FTD patient collections (one Australian and one Spanish, combined n = 190), to examine C9ORF72 expansion allele length in a subset of FTD patients, and to examine C9ORF72 allele length in ‘non-expansion’ patients (those with <30 repeats). The C9ORF72 repeat expansion was detected in 5–17% of patients (21–41% of familial FTD patients). For one family, the expansion was present in the proband but absent in the mother, who was diagnosed with dementia at age 68. No association was found between C9ORF72 non-expanded allele length and age of onset and in the Spanish sample mean allele length was shorter in cases than in controls. Southern blotting analysis revealed that one of the nine ‘expansion-positive’ patients examined, who had neuropathologically confirmed frontotemporal lobar degeneration with TDP-43 pathology, harboured an ‘intermediate’ allele with a mean size of only ∼65 repeats. Our study indicates that the C9ORF72 repeat expansion accounts for a significant proportion of Australian and Spanish FTD cases. However, C9ORF72 allele length does not influence the age at onset of ‘non-expansion’ FTD patients in the series examined. Expansion of the C9ORF72 allele to as little as ∼65 repeats may be sufficient to cause disease.

NEK1 mutations in familial amyotrophic lateral sclerosis

Sir, Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by adult-onset loss of motor neurons. Five to 10% of all ALS cases are familial ALS. To date, more than 20 genes have been implicated in causing familial ALS, with the discovery of mutations in CHCHD10 (Bannwarth et al. , 2014) and TBK1 (Cirulli et al. , 2015; Freischmidt et al. , 2015) representing the latest examples for monogenic causes of ALS. Most recently, whole exome sequencing of ALS patients suggested an association of heterozygous loss-of-function mutations in NEK1 with ALS. However, this observation was made in a cohort of mostly sporadic patients, and the result was only significant in a combined analysis of the discovery and the replication cohort (Cirulli et al. , 2015), making further validation essential. To assess the association between NEK1 variants and familial ALS we analysed whole exome sequence data of 265 familial ALS index patients and 827 control individuals. A subset of these exome sequence data has recently led to the discovery of mutations in TBK1 as a cause for ALS in an exome-wide mutational burden analysis (Freischmidt et al. , 2015). The patients with familial ALS were selected from families with two or more affected individuals from European countries (Germany, Sweden, Finland, Denmark, Switzerland, and Portugal) following a negative screen for SOD1 and C9orf72 mutations as described previously (Freischmidt et al. , 2015). In-house control exomes ( n = 827) from Germany were used to compare the variant burden in NEK1 . All ALS patients were diagnosed according to the EFNS Consensus criteria (Andersen et al. , 2012). Control subjects were comprised of healthy parents of children with various diseases, healthy control tissues of individuals with tumour diseases and 200 individuals of the KORA study. With informed written consent and approval by …

Polymerase chain reaction and Southern blot-based analysis of the C9orf72 hexanucleotide repeat in different motor neuron diseases

The GGGGCC-hexanucleotide repeat expansion in C9orf72 is the most common genetic cause of familial amyotrophic lateral sclerosis and frontotemporal dementia. This study determined the frequency of C9orf72 repeat expansions in different motor neuron diseases (amyotrophic lateral sclerosis (ALS), motor neuron diseases affecting primarily the first or the second motor neuron and hereditary spastic paraplegia). Whereas most studies on C9orf72 repeat expansions published so far rely on a polymerase chain reaction-based screening, we applied both polymerase chain reaction-based techniques and Southern blotting. Furthermore, we determined the sensitivity and specificity of Southern blotting of the C9orf72 hexanucleotide repeat in DNA derived from lymphoblastoid cell lines. C9orf72 repeat expansions were found in 27.1% out of 166 familial ALS patients, only once in 68 sporadic ALS patients, and not in 61 hereditary spastic paraplegia patients or 52 patients with motor neuron diseases affecting clinically primarily either the first or the second motor neuron. We found hints for a correlation between C9orf72 repeat length and the age of onset. Somatic instability of the C9orf72 repeat was observed in lymphoblastoid cell lines compared with DNA derived from whole blood from the same patient and therefore caution is warranted for repeat length determination in immortalized cell lines.

A novel optineurin truncating mutation and three glaucoma-associated missense variants in patients with familial amyotrophic lateral sclerosis in Germany

Mutations in the optineurin (OPTN) gene have been associated with normal tension glaucoma and with amyotrophic lateral sclerosis (ALS). Here, we screened German familial ALS cases for OPTN mutations to gain additional insight into the spectrum and pathogenic relevance of this gene for ALS. One hundred familial German ALS cases and 148 control subjects were screened for OPTN mutations by sequence analysis of the complete OPTN coding sequence, and phenotypes of OPTN mutant patients were described. We identified a novel heterozygous truncating OPTN mutation p.Lys440Asnfs*8 in 1 ALS family with an aggressive ALS disease phenotype. This mutation abolishes protein domains crucial for nuclear factor κB signaling. Moreover, we detected 3 different nonsynonymous sequence variants, which have been described previously as risk factors for primary retinal ganglion cell degeneration in normal tension glaucoma. Two of them were detected on the same allele in a family that also carries a p.Asn352Ser disease mutation in the ALS gene TARDBP. All OPTN mutant patients presented with typical spinal onset ALS. Taken together, we detected a novel truncating OPTN mutation associated with an aggressive form of ALS and confirmed that OPTN mutations are a rare cause of ALS. In addition our data suggest that in some cases plausibly more than 1 mutation in OPTN or another ALS gene might be needed to cause ALS. Finally, our findings show that motoneurons and retinal ganglion cells, which are both projecting central nervous system neurons, might share common susceptibility factors.