The mitochondrial seryl-tRNA synthetase SARS2 modifies onset in spastic paraplegia type 4.

PURPOSE: Hereditary spastic paraplegia type 4 is extremely variable in age at onset; the same variant can cause onset at birth or in the eighth decade. We recently discovered that missense variants in SPAST, which influences microtubule dynamics, are associated with earlier onset and more severe disease than truncating variants, but even within the early and late-onset groups there remained significant differences in onset. Given the rarity of the condition, we adapted an extreme phenotype approach to identify genetic modifiers of onset. METHODS: We performed a genome-wide association study on 134 patients bearing truncating pathogenic variants in SPAST, divided into early- and late-onset groups (aged ≤15 and ≥45 years, respectively). A replication cohort of 419 included patients carrying either truncating or missense variants. Finally, age at onset was analyzed in the merged cohort (N = 553). RESULTS: We found 1 signal associated with earlier age at onset (rs10775533, P = 8.73E-6) in 2 independent cohorts and in the merged cohort (N = 553, Mantel-Cox test, P < .0001). Western blotting in lymphocytes of 20 patients showed that this locus tends to upregulate SARS2 expression in earlier-onset patients. CONCLUSION: SARS2 overexpression lowers the age of onset in hereditary spastic paraplegia type 4. Lowering SARS2 or improving mitochondrial function could thus present viable approaches to therapy.

Hereditary spastic paraplegia type 5: natural history, biomarkers and a randomized controlled trial.

Spastic paraplegia type 5 (SPG5) is a rare subtype of hereditary spastic paraplegia, a highly heterogeneous group of neurodegenerative disorders defined by progressive neurodegeneration of the corticospinal tract motor neurons. SPG5 is caused by recessive mutations in the gene CYP7B1 encoding oxysterol-7α-hydroxylase. This enzyme is involved in the degradation of cholesterol into primary bile acids. CYP7B1 deficiency has been shown to lead to accumulation of neurotoxic oxysterols. In this multicentre study, we have performed detailed clinical and biochemical analysis in 34 genetically confirmed SPG5 cases from 28 families, studied dose-dependent neurotoxicity of oxysterols in human cortical neurons and performed a randomized placebo-controlled double blind interventional trial targeting oxysterol accumulation in serum of SPG5 patients. Clinically, SPG5 manifested in childhood or adolescence (median 13 years). Gait ataxia was a common feature. SPG5 patients lost the ability to walk independently after a median disease duration of 23 years and became wheelchair dependent after a median 33 years. The overall cross-sectional progression rate of 0.56 points on the Spastic Paraplegia Rating Scale per year was slightly lower than the longitudinal progression rate of 0.80 points per year. Biochemically, marked accumulation of CYP7B1 substrates including 27-hydroxycholesterol was confirmed in serum (n = 19) and cerebrospinal fluid (n = 17) of SPG5 patients. Moreover, 27-hydroxycholesterol levels in serum correlated with disease severity and disease duration. Oxysterols were found to impair metabolic activity and viability of human cortical neurons at concentrations found in SPG5 patients, indicating that elevated levels of oxysterols might be key pathogenic factors in SPG5. We thus performed a randomized placebo-controlled trial (EudraCT 2015-000978-35) with atorvastatin 40 mg/day for 9 weeks in 14 SPG5 patients with 27-hydroxycholesterol levels in serum as the primary outcome measure. Atorvastatin, but not placebo, reduced serum 27-hydroxycholesterol from 853 ng/ml [interquartile range (IQR) 683-1113] to 641 (IQR 507-694) (-31.5%, P = 0.001, Mann-Whitney U-test). Similarly, 25-hydroxycholesterol levels in serum were reduced. In cerebrospinal fluid 27-hydroxycholesterol was reduced by 8.4% but this did not significantly differ from placebo. As expected, no effects were seen on clinical outcome parameters in this short-term trial. In this study, we define the mutational and phenotypic spectrum of SPG5, examine the correlation of disease severity and progression with oxysterol concentrations, and demonstrate in a randomized controlled trial that atorvastatin treatment can effectively lower 27-hydroxycholesterol levels in serum of SPG5 patients. We thus demonstrate the first causal treatment strategy in hereditary spastic paraplegia.

Novel Compound Heterozygous Spatacsin Mutations in a Greek Kindred with Hereditary Spastic Paraplegia SPG11 and Dementia.

SPG11 belongs to the autosomal recessive hereditary spastic paraplegias (HSP) and presents during childhood or puberty with a complex clinical phenotype encompassing learning difficulties, ataxia, peripheral neuropathy, amyotrophy, and mental retardation. We hereby present the case of a 30-year-old female patient with complex autosomal recessive HSP with thinning of the corpus callosum (TCC) and dementia that was compound heterozygous with two novel mutations in the SPG11 gene. Sequence analysis of the SPG11 gene revealed two novel mutations in a compound heterozygous state in the index patient (c.2431C>T/p.Gln811Ter and c.6755_6756insT/p.Glu2252Aspfs*88). MRI showed abnormal TCC, white matter (WM) hyperintensities periventricularly, and the 'ears of the lynx' sign. Diffusion tensor imaging showed a mild-to-moderate decrease in fractional anisotropy and an increase in mean diffusivity in WM compared to age-matched controls, while magnetic resonance spectroscopy showed abnormal findings in affected WM with a decrease in N-acetyl-aspartate in WM regions of interest. This is the first SPG11 kindred from the Greek population to be reported in the medical literature.

Chenodeoxycholic acid rescues axonal degeneration in induced pluripotent stem cell-derived neurons from spastic paraplegia type 5 and cerebrotendinous xanthomatosis patients.

BACKGROUND: Biallelic mutations in CYP27A1 and CYP7B1, two critical genes regulating cholesterol and bile acid metabolism, cause cerebrotendinous xanthomatosis (CTX) and hereditary spastic paraplegia type 5 (SPG5), respectively. These rare diseases are characterized by progressive degeneration of corticospinal motor neuron axons, yet the underlying pathogenic mechanisms and strategies to mitigate axonal degeneration remain elusive. METHODS: To generate induced pluripotent stem cell (iPSC)-based models for CTX and SPG5, we reprogrammed patient skin fibroblasts into iPSCs by transducing fibroblast cells with episomal vectors containing pluripotency factors. These patient-specific iPSCs, as well as control iPSCs, were differentiated into cortical projection neurons (PNs) and examined for biochemical alterations and disease-related phenotypes. RESULTS: CTX and SPG5 patient iPSC-derived cortical PNs recapitulated several disease-specific biochemical changes and axonal defects of both diseases. Notably, the bile acid chenodeoxycholic acid (CDCA) effectively mitigated the biochemical alterations and rescued axonal degeneration in patient iPSC-derived neurons. To further examine underlying disease mechanisms, we developed CYP7B1 knockout human embryonic stem cell (hESC) lines using CRISPR-cas9-mediated gene editing and, following differentiation, examined hESC-derived cortical PNs. Knockout of CYP7B1 resulted in similar axonal vesiculation and degeneration in human cortical PN axons, confirming a cause-effect relationship between gene deficiency and axonal degeneration. Interestingly, CYP7B1 deficiency led to impaired neurofilament expression and organization as well as axonal degeneration, which could be rescued with CDCA, establishing a new disease mechanism and therapeutic target to mitigate axonal degeneration. CONCLUSIONS: Our data demonstrate disease-specific lipid disturbances and axonopathy mechanisms in human pluripotent stem cell-based neuronal models of CTX and SPG5 and identify CDCA, an established treatment of CTX, as a potential pharmacotherapy for SPG5. We propose this novel treatment strategy to rescue axonal degeneration in SPG5, a currently incurable condition.

Cerebrotendinous xanthomatosis presenting with severe externalized disorder: improvement after one year of treatment with chenodeoxycholic Acid.

Cerebrotendinous xanthomatosis (CTX) is a rare inborn disorder of sterol storage with autosomal recessive inheritance and a variable clinical presentation. We describe two siblings with an early psychiatric presentation of CTX-associated attention-deficit/hyperactivity disorder and oppositional defiant disorder, also associated with a mild intellectual disability and major behavioral impairments. In both cases, treatment with chenodeoxycholic acid improved externalized symptoms and a partial recovery of cognitive impairments was observed. This suggests that CTX is potentially reversible, demonstrating the need for early diagnosis and treatment of this disorder before irreversible neurological lesions can occur.

No supportive evidence for TIA1 gene mutations in a European cohort of ALS-FTD spectrum patients.

We evaluated the genetic contribution of the T cell-restricted intracellular antigen-1 gene (TIA1) in a European cohort of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) patients. Exonic resequencing of TIA1 in 1120 patients (693 FTD, 341 ALS, 86 FTD-ALS) and 1039 controls identified in total 5 rare heterozygous missense variants, affecting the TIA1 low-complexity domain (LCD). Only 1 missense variant, p.Met290Thr, identified in a familial FTD patient with disease onset at 64 years, was absent from controls yet received a combined annotation-dependent depletion score of 11.42. By contrast, 3 of the 4 variants also detected in unaffected controls, p.Val294Glu, p.Gln318Arg, and p.Ala381Thr, had combined annotation-dependent depletion scores greater than 20. Our findings in a large European patient-control series indicate that variants in TIA1 are not a common cause of ALS and FTD. The observation of recurring TIA1 missense variants in unaffected individuals lead us to conclude that the exact genetic contribution of TIA1 to ALS and FTD pathogenesis remains to be further elucidated.

Recovery from spinal cord injury in tumor necrosis factor-alpha, signal transducers and activators of transcription 4 and signal transducers and activators of transcription 6 null mice.

Tumor necrosis factor-alpha is a central cytokine involved in the regulation of the innate immune response. Signal transducers and activators of transcription 4 and signal transducers and activators of transcription 6 are second messengers mediating the Th1 and Th2-specific immune responses, respectively. We studied the outcome of spinal cord injury with respect to the locomotion and axonal regeneration in tumor necrosis factor-alpha, signal transducers and activators of transcription 4 and signal transducers and activators of transcription 6 knockout mice. Locomotor behavior after injury differed between mouse strains, but not between wild-type and the knockout genotypes of the same strain. Regeneration of descending tracts, assessed by fluorogold/fluororuby retrograde double-labeling, however, appeared hampered by Th2 deficiency.

Phenotypic diversity associated with the MT-TV gene m.1644G>A mutation, a matter of quantity.

We describe four patients from three independent families with the m.1644G>A in the MT-TV gene, previously reported without demonstration of its deleterious impact. Very high mutation proportion co-segregated with cytochrome oxidase defect in single muscle fibers and respiratory defect in cybrids as shown by spectrophotometric assays and polarography. The mutation appeared to have a very steep threshold effect with asymptomatic life up to 70% mutation proportion, progressive encephalopathy above 80% and severe Leigh-like syndrome above 95% mutation. One patient did not fit within that frame but presented with characteristics suggesting the presence of an additional disease.

Cholestenoic acids regulate motor neuron survival via liver X receptors.

Cholestenoic acids are formed as intermediates in metabolism of cholesterol to bile acids, and the biosynthetic enzymes that generate cholestenoic acids are expressed in the mammalian CNS. Here, we evaluated the cholestenoic acid profile of mammalian cerebrospinal fluid (CSF) and determined that specific cholestenoic acids activate the liver X receptors (LXRs), enhance islet-1 expression in zebrafish, and increase the number of oculomotor neurons in the developing mouse in vitro and in vivo. While 3ß,7α-dihydroxycholest-5-en-26-oic acid (3ß,7α-diHCA) promoted motor neuron survival in an LXR-dependent manner, 3ß-hydroxy-7-oxocholest-5-en-26-oic acid (3ßH,7O-CA) promoted maturation of precursors into islet-1+ cells. Unlike 3ß,7α-diHCA and 3ßH,7O-CA, 3ß-hydroxycholest-5-en-26-oic acid (3ß-HCA) caused motor neuron cell loss in mice. Mutations in CYP7B1 or CYP27A1, which encode enzymes involved in cholestenoic acid metabolism, result in different neurological diseases, hereditary spastic paresis type 5 (SPG5) and cerebrotendinous xanthomatosis (CTX), respectively. SPG5 is characterized by spastic paresis, and similar symptoms may occur in CTX. Analysis of CSF and plasma from patients with SPG5 revealed an excess of the toxic LXR ligand, 3ß-HCA, while patients with CTX and SPG5 exhibited low levels of the survival-promoting LXR ligand 3ß,7α-diHCA. Moreover, 3ß,7α-diHCA prevented the loss of motor neurons induced by 3ß-HCA in the developing mouse midbrain in vivo.Our results indicate that specific cholestenoic acids selectively work on motor neurons, via LXR, to regulate the balance between survival and death.

Lugaro's forgotten legacy: the hypothesis of negative neurotropism.

Among the most fascinating riddles in neuroscience is the one concerning the poor regeneration capacity of the adult mammalian CNS. A central aetiological hypothesis for the lack of axonal regeneration in the CNS concerns the inhibitory role of myelin components of the white matter. The main exponent of this hypothesis in the 1980s and 1990s has been Martin Schwab, although before him Martin Berry and others had suggested an inhibitory role for CNS myelin. However, a hypothesis for a negative neurotropic action exerted by CNS white matter was formulated by Lugaro already in 1906. This article is a belated tribute to Lugaro's original contribution in the field of neuroregeneration.

Partial recovery after treatment of chronic paraplegia in rat.

While acute spinal cord injury has been the object of intensive research, chronic spinal cord injury has received less attention although most clinical cases of spinal cord injury become chronic. We attempted to surgically "repair" chronic and acute spinal cord injury in a complete transection rat model using a multiple peripheral nerve grafting protocol. The lesion extent was assessed by magnetic resonance imaging (MRI) before the repair procedure. Rats were treated immediately after injury or at 2, 4, or 8 months postinjury. Standard behavioral methods were used to evaluate functional recovery. Two novel tests, the Bipedal Test and the Head-scratch test, were also employed to evaluate hindpaw positioning, interlimb coordination, and stepping rhythmicity, and to indicate rostrocaudal pathway regeneration. MRI helped guide the treatment procedure that was applied to animals with chronic injury. Treated animals demonstrated significant motor recovery. Axonal regeneration resultant to treatment was demonstrated histologically. The results suggest that not only acute but also chronic total paraplegia can be reversed to a moderate degree in rats with regard to hindlimb motor function.