Progressive myoclonus epilepsies-Residual unsolved cases have marked genetic heterogeneity including dolichol-dependent protein glycosylation pathway genes

Progressive myoclonus epilepsies (PMEs) comprise a group of clinically and genetically heterogeneous rare diseases. Over 70% of PME cases can now be molecularly solved. Known PME genes encode a variety of proteins, many involved in lysosomal and endosomal function. We performed whole-exome sequencing (WES) in 84 (78 unrelated) unsolved PME-affected individuals, with or without additional family members, to discover novel causes. We identified likely disease-causing variants in 24 out of 78 (31%) unrelated individuals, despite previous genetic analyses. The diagnostic yield was significantly higher for individuals studied as trios or families (14/28) versus singletons (10/50) (OR = 3.9, p value = 0.01, Fisher's exact test). The 24 likely solved cases of PME involved 18 genes. First, we found and functionally validated five heterozygous variants in NUS1 and DHDDS and a homozygous variant in ALG10, with no previous disease associations. All three genes are involved in dolichol-dependent protein glycosylation, a pathway not previously implicated in PME. Second, we independently validate SEMA6B as a dominant PME gene in two unrelated individuals. Third, in five families, we identified variants in established PME genes; three with intronic or copy-number changes (CLN6, GBA, NEU1) and two very rare causes (ASAH1, CERS1). Fourth, we found a group of genes usually associated with developmental and epileptic encephalopathies, but here, remarkably, presenting as PME, with or without prior developmental delay. Our systematic analysis of these cases suggests that the small residuum of unsolved cases will most likely be a collection of very rare, genetically heterogeneous etiologies.Peer reviewe

Alteration of endosomal trafficking is associated with early-onset parkinsonism caused by SYNJ1 mutations

Recently, a new form of autosomal recessive early-onset parkinsonism (PARK20), due to mutations in the gene encoding the phosphoinositide phosphatase, Synaptojanin 1 (Synj1), has been reported. Several genes responsible for hereditary forms of Parkinson's disease are implicated in distinct steps of the endolysosomal pathway. However, the nature and the degree of endocytic membrane trafficking impairment in early-onset parkinsonism remains elusive. Here, we show that depletion of Synj1 causes drastic alterations of early endosomes, which become enlarged and more numerous, while it does not affect the morphology of late endosomes both in non-neuronal and neuronal cells. Moreover, Synj1 loss impairs the recycling of transferrin, while it does not alter the trafficking of the epidermal growth factor receptor. The ectopic expression of Synj1 restores the functions of early endosomes, and rescues these trafficking defects in depleted cells. Importantly, the same alterations of early endosomal compartments and trafficking defects occur in fibroblasts of PARK20 patients. Our data indicate that Synj1 plays a crucial role in regulating the homeostasis and functions of early endosomal compartments in different cell types, and highlight defective cellular pathways in PARK20. In addition, they strengthen the link between endosomal trafficking and Parkinson's disease

Multinationals and U.S. productivity leadership: evidence from Great Britain

We study the productivity of U.S. and other foreign-owned plants in the United Kingdom. Using a new data set that can identify for the first time domestic U.K. MNEs in such a study, we find that U.K. MNEs are less productive than U.S. affiliates, but as productive as non-U.S. foreign affiliates. Exploiting dynamic variation in our data, we find evidence suggesting that this additional U.S. advantage is due to the takeover of already highly productive U.K. plants rather than the sharing of superior firm-specific assets. The study also features a novel approach to TFP calculation

Powerhouse failure and oxidative damage in autosomal recessive spastic ataxia of Charlevoix-Saguenay

Autosomal recessive spastic ataxia of Charlevoix- Saguenay (ARSACS) is a neurodegenerative disease due to mutations in SACS, which encodes sacsin, a protein localized on the mitochondrial surface and possibly involved in mitochondrial dynamics. In view of the possible mitochondrial involvement of sacsin, we investigated mitochondrial activity at functional and molecular level in skin fibroblasts obtained from ARSACS patients. We observed remarkable bioenergetic damage in ARSACS cells, as indicated by reduced basal, adenosine triphosphate (ATP)- linked and maximal mitochondrial respiration rate, and by reduced respiratory chain activities and mitochondrial ATP synthesis. These phenomena were associated with increased reactive oxygen species production and oxidative nuclear DNA damage. Our results suggest that loss of sacsin is associated with oxidative stress and mitochondrial dysfunction, and thus highlight a novel mechanism in the pathogenesis of ARSACS. The involvement of mitochondria and oxidative stress in disease pathogenesis has been described in a number of other neurodegenerative diseases. Therefore, on the basis of our findings, which suggest a potential therapeutic role for antioxidant agents, ARSACS seems to fall within a larger group of disorders

Spastic paraplegia with thin corpus callosum: description of 20 new families, refinement of the SPG11 locus, candidate gene analysis and evidence of genetic heterogeneity.

We studied 20 Mediterranean families (40 patients) with autosomal recessive hereditary spastic paraplegia and thin corpus callosum (ARHSP-TCC, MIM 604360) to characterize their clinical and genetic features. In six families (17 patients) of Algerian Italian, Moroccan, and Portuguese ancestry, we found data consistent with linkage to the SPG11 locus on chromosome 15q13-15, whereas, in four families (nine patients of Italian, French, and Portuguese ancestry) linkage to the SPG11 locus could firmly be excluded, reinforcing the notion that ARHSP-TCC is genetically heterogeneous. Patients from linked and unlinked families could not be distinguished on the basis of clinical features alone. In SPG11-linked kindred, haplotype reconstruction allowed significant refinement to 6 cM, of the minimal chromosomal interval, but analysis of two genes (MAP1A and SEMA6D) in this region did not identify causative mutations. Our findings suggest that ARHSP-TCC is the most frequent form of ARHSP in Mediterranean countries and that it is particularly frequent in Italy