George H. Gorrie

Mutations in UBQLN2 cause dominant X-linked juvenile and adult-onset ALS and ALS/dementia

Amyotrophic lateral sclerosis (ALS) is a paralytic and usually fatal disorder caused by motor-neuron degeneration in the brain and spinal cord. Most cases of ALS are sporadic but about 5–10% are familial. Mutations in superoxide dismutase 1 (SOD1), TAR DNA-binding protein (TARDBP, also known as TDP43) and fused in sarcoma (FUS, also known as translocated in liposarcoma (TLS)) account for approximately 30% of classic familial ALS. Mutations in several other genes have also been reported as rare causes of ALS or ALS-like syndromes. The causes of the remaining cases of familial ALS and of the vast majority of sporadic ALS are unknown. Despite extensive studies of previously identified ALS-causing genes, the pathogenic mechanism underlying motor-neuron degeneration in ALS remains largely obscure. Dementia, usually of the frontotemporal lobar type, may occur in some ALS cases. It is unclear whether ALS and dementia share common aetiology and pathogenesis in ALS/dementia. Here we show that mutations in UBQLN2, which encodes the ubiquitin-like protein ubiquilin 2, cause dominantly inherited, chromosome-X-linked ALS and ALS/dementia. We describe novel ubiquilin 2 pathology in the spinal cords of ALS cases and in the brains of ALS/dementia cases with or without UBQLN2 mutations. Ubiquilin 2 is a member of the ubiquilin family, which regulates the degradation of ubiquitinated proteins. Functional analysis showed that mutations in UBQLN2 lead to an impairment of protein degradation. Therefore, our findings link abnormalities in ubiquilin 2 to defects in the protein degradation pathway, abnormal protein aggregation and neurodegeneration, indicating a common pathogenic mechanism that can be exploited for therapeutic intervention.

Mutations in the SPG7 gene cause chronic progressive external ophthalmoplegia through disordered mitochondrial DNA maintenance

Progressive external ophthalmoplegia (PEO) is a canonical feature of mitochondrial disease, but in many patients its genetic basis is unknown. Using exome sequencing, Pfeffer et al. identify mutations in SPG7 as an important cause of PEO associated with spasticity and ataxia, and uncover evidence of disordered mtDNA maintenance in patients.

Dendritic spinopathy in transgenic mice expressing ALS/dementia-linked mutant UBQLN2

Significance Mutations in the UBQLN2 gene, which encodes the ubiquitin-like protein ubiquilin2 (UBQLN2) have been shown to cause ALS and ALS/dementia. Ubiquilin2 links familial and sporadic forms of the disease through pathology observed in the spinal cords of all ALS cases and in the brains of ALS/dementia cases with or without UBQLN2 mutations. In this communication, we develop and characterize a mouse model of mutant UBQLN2-linked dementia. We demonstrate that mutant mice develop impairment in the protein degradation pathway, abnormal protein aggregation, synaptic dysfunction, and cognitive deficits. This model provides a useful tool to further study dementia and develop rational therapies. Mutations in the gene encoding ubiquilin2 (UBQLN2) cause amyotrophic lateral sclerosis (ALS), frontotemporal type of dementia, or both. However, the molecular mechanisms are unknown. Here, we show that ALS/dementia-linked UBQLN2P497H transgenic mice develop neuronal pathology with ubiquilin2/ubiquitin/p62-positive inclusions in the brain, especially in the hippocampus, recapitulating several key pathological features of dementia observed in human patients with UBQLN2 mutations. A major feature of the ubiquilin2-related pathology in these mice, and reminiscent of human disease, is a dendritic spinopathy with protein aggregation in the dendritic spines and an associated decrease in dendritic spine density and synaptic dysfunction. Finally, we show that the protein inclusions in the dendritic spines are composed of several components of the proteasome machinery, including UbG76V–GFP, a representative ubiquitinated protein substrate that is accumulated in the transgenic mice. Our data, therefore, directly link impaired protein degradation to inclusion formation that is associated with synaptic dysfunction and cognitive deficits. These data imply a convergent molecular pathway involving synaptic protein recycling that may also be involved in other neurodegenerative disorders, with implications for development of widely applicable rational therapeutics.

Gender difference in levels of Cu/Zn superoxide dismutase (SOD1) in cerebrospinal fluid of patients with amyotrophic lateral sclerosis.

Currently the best studied mechanism for amyotrophic lateral sclerosis (ALS) is the one caused by mutations in the gene for cytosolic Cu/Zn-binding superoxide dismutase (SOD1). Mutant SOD1 protein causes motor neuron degeneration due to the gain of a novel toxic function. To evaluate the relevance of SOD1 levels in cerebrospinal fluid (CSF) in ALS patients, the SOD1 concentration was immunoassayed in the CSF of 11 patients with ALS and 19 neurological controls. The mean level of SOD1 in CSF from all samples was 45.5+/−11.3 ng/ml. There was no statistically significant difference between the levels of SOD1 in CSF of ALS patients and neurological control subjects. Here we show that the SOD1 concentration in the CSF is significantly higher in male ALS patients (54.0+/−9.0 ng/ml) compared to female ALS patients (38.1+/−6.4 ng/ml) (p=0.007). This gender difference is not observed in the CSF of neurological controls. This is the first report of a potential gender difference in levels of SOD1 in CSF of ALS patients. Further investigation of larger sample groups is needed to determine whether it is relevant to gender related differences in disease incidence.

Management of sialorrhoea in motor neuron disease: a survey of current UK practice

Abstract Our objective was to better understand UK-wide practice in managing sialorrhoea in motor neuron disease among specialist clinicians. We used a survey of neurologists in the UK with a special interest in motor neuron disease designed to establish clinicians’ attitudes towards treatment options and resources for sialorrhoea management. Twenty-three clinicians replied, representing 21 centres. Sixteen centres were specialist MND Care Centres. Clinicians estimated seeing a total of 1391 newly diagnosed patients with MND in 2011. One hundred and ninety-three patients were described. Forty-two percent of patients reviewed in clinicians’ last clinic had sialorrhoea and 46% of those with sialorrhoea had uncontrolled symptoms. Clinicians’ preferred drugs were hyoscine patches, amitriptyline, carbocisteine and botulinum toxin. Botulinum toxin was used in 14 centres. Risk of dysphagia and staff skills were identified as the main barriers to botulinum toxin use. This survey suggests that there may be as many as 1700 patients with MND in the UK who have symptoms of sialorrhoea and that symptoms may be poorly controlled in nearly half. Treatment strategies varied, reflecting the lack of evidence based guidelines. The use of specialist treatments was influenced by local infrastructure. This study highlights the need for further work to develop evidence based guidance.

Genetic epidemiology of motor neuron disease-associated variants in the Scottish population

Genetic understanding of motor neuron disease (MND) has evolved greatly in the past 10 years, including the recent identification of association between MND and variants in TBK1 and NEK1. Our aim was to determine the frequency of pathogenic variants in known MND genes and to assess whether variants in TBK1 and NEK1 contribute to the burden of MND in the Scottish population. SOD1, TARDBP, OPTN, TBK1, and NEK1 were sequenced in 441 cases and 400 controls. In addition to 44 cases known to carry a C9orf72 hexanucleotide repeat expansion, we identified 31 cases and 2 controls that carried a loss-of-function or pathogenic variant. Loss-of-function variants were found in TBK1 in 3 cases and no controls and, separately, in NEK1 in 3 cases and no controls. This study provides an accurate description of the genetic epidemiology of MND in Scotland and provides support for the contribution of both TBK1 and NEK1 to MND susceptibility in the Scottish population.

A multicentre evaluation of oropharyngeal secretion management practices in amyotrophic lateral sclerosis

Abstract Failure to clear oral secretions can be debilitating for patients with amyotrophic lateral sclerosis (ALS), but the treatment of this symptom is poorly defined and there is no consensus on best practice. The objective of this study was to identify the treatments that are commonly prescribed, and to describe how experienced clinicians manage a patient with treatment resistant symptoms. Twenty-three clinicians were approached, of which 19 from 16 centres across the UK provided case report forms for a total of 119 ALS patients identified as having problematic oral secretions. The use of five anticholinergics, salivary gland botulinum toxin injections, conservative management approaches and carbocisteine were reported. Of the 72 patients who were evaluated following the initiation of a first anticholinergic, 61% had symptomatic improvement. Only 19% of patients achieved symptomatic improvement with the use of an alternative anticholinergic when an initial anticholinergic achieved no symptomatic improvement. Problems with thick and thin secretions often coexisted, with 37% of patients receiving treatment for both types of problem. In conclusion, a variety of treatment options are employed by expert clinicians for problematic oral secretions in ALS patients. The variation in management highlights the need for further prospective research in this area.

Improved PCR based methods for detecting C9orf72 hexanucleotide repeat expansions.

Due to the GC-rich, repetitive nature of C9orf72 hexanucleotide repeat expansions, PCR based detection methods are challenging. Several limitations of PCR have been reported and overcoming these could help to define the pathogenic range. There is also a need to develop improved repeat-primed PCR assays which allow detection even in the presence of genomic variation around the repeat region. We have optimised PCR conditions for the C9orf72 hexanucleotide repeat expansion, using betaine as a co-solvent and specific cycling conditions, including slow ramping and a high denaturation temperature. We have developed a flanking assay, and repeat-primed PCR assays for both 3′ and 5′ ends of the repeat expansion, which when used together provide a robust strategy for detecting the presence or absence of expansions greater than ∼100 repeats, even in the presence of genomic variability at the 3′ end of the repeat. Using our assays, we have detected repeat expansions in 47/442 Scottish ALS patients. Furthermore, we recommend the combined use of these assays in a clinical diagnostic setting.

Corrigendum to “Genetic epidemiology of motor neuron disease-associated variants in the Scottish population.” [Neurobiol. Aging 51 (2017) 178.e11–178.e20]

“The authors thank the patients for consenting to research. In addition, they acknowledge Alona Sosinsky and the Imperial College BRC Genomics facility for bioinformatics support. They acknowledge Generation Scotland for providing control samples and thank Shona Kerr and Archie Campbell for assistance in provision of Generation Scotland samples. The authors acknowledge Cat Graham for providing statistical guidance and also thank David Parry and Sophie Marion de Proce for providing helpful comments on the manuscript.

A question of taste

A 38-year-old woman presented with bilateral lower facial weakness and reduced taste, but preserved involuntary facial movements and smell.