Choroid plexus mis-splicing and altered cerebrospinal fluid composition in myotonic dystrophy type 1.

Myotonic dystrophy type 1 is a dominantly inherited multisystemic disease caused by CTG tandem repeat expansions in the DMPK 3' untranslated region. These expanded repeats are transcribed and produce toxic CUG RNAs that sequester and inhibit activities of the MBNL family of developmental RNA processing factors. Although myotonic dystrophy is classified as a muscular dystrophy, the brain is also severely affected by an unusual cohort of symptoms, including hypersomnia, executive dysfunction, as well as early onsets of tau/MAPT pathology and cerebral atrophy. To address the molecular and cellular events that lead to these pathological outcomes, we recently generated a mouse Dmpk CTG expansion knock-in model and identified choroid plexus epithelial cells as particularly affected by the expression of toxic CUG expansion RNAs. To determine if toxic CUG RNAs perturb choroid plexus functions, alternative splicing analysis was performed on lateral and hindbrain choroid plexi from Dmpk CTG knock-in mice. Choroid plexus transcriptome-wide changes were evaluated in Mbnl2 knockout mice, a developmental-onset model of myotonic dystrophy brain dysfunction. To determine if transcriptome changes also occurred in the human disease, we obtained post-mortem choroid plexus for RNA-seq from neurologically unaffected (two females, three males; ages 50-70 years) and myotonic dystrophy type 1 (one female, three males; ages 50-70 years) donors. To test that choroid plexus transcriptome alterations resulted in altered CSF composition, we obtained CSF via lumbar puncture from patients with myotonic dystrophy type 1 (five females, five males; ages 35-55 years) and non-myotonic dystrophy patients (three females, four males; ages 26-51 years), and western blot and osmolarity analyses were used to test CSF alterations predicted by choroid plexus transcriptome analysis. We determined that CUG RNA induced toxicity was more robust in the lateral choroid plexus of Dmpk CTG knock-in mice due to comparatively higher Dmpk and lower Mbnl RNA levels. Impaired transitions to adult splicing patterns during choroid plexus development were identified in Mbnl2 knockout mice, including mis-splicing previously found in Dmpk CTG knock-in mice. Whole transcriptome analysis of myotonic dystrophy type 1 choroid plexus revealed disease-associated RNA expression and mis-splicing events. Based on these RNA changes, predicted alterations in ion homeostasis, secretory output and CSF composition were confirmed by analysis of myotonic dystrophy type 1 CSF. Our results implicate choroid plexus spliceopathy and concomitant alterations in CSF homeostasis as an unappreciated contributor to myotonic dystrophy type 1 CNS pathogenesis.

Milestones of progression in myotonic dystrophy type 1 and type 2.

INTRODUCTION/AIMS: Disease progression in myotonic dystrophy (DM) is marked by milestone events when functional thresholds are crossed. DM type 2 (DM2) is considered less severe than DM type 1 (DM1), but it is unknown whether this applies uniformly to all features. We compared the age-dependent risk for milestone events in DM1 and DM2 and tested for associations with age of onset and sex. METHODS: We studied a large cohort of adult participants in a national registry of DM1 and DM2. Using annual surveys from participants, we ascertained milestone events for motor involvement (use of cane, walker, ankle brace, wheelchair, or ventilatory device), systemic involvement (diabetes, pacemaker, cancer), loss of employment due to DM, and death. RESULTS: Mean follow-up of registry participants (929 DM1 and 222 DM2 patients) was 7 years. Disability and motor milestones occurred at earlier ages in DM1 than in DM2. In contrast, the risk of diabetes was higher and tended to occur earlier in DM2 (hazard ratio [HR], 0.56; P ≤ .001). In DM1, the milestone events tended to occur earlier, and life expectancy was reduced, when symptoms began at younger ages. In DM1, men were at greater risk for disability (HR, 1.34; P ≤ .01), use of ankle braces (HR, 1.41; P = .02), and diabetes (HR, 2.2; P ≤ .0001), whereas women were at greater risk for needing walkers (HR, 0.68; P = .001) or malignancy (HR, 0.66; P ≤ .01). DISCUSSION: Milestone events recorded through registries can be used to assess long-term impact of DM in large cohorts. Except for diabetes, the age-related risk of milestone events is greater in DM1 than in DM2.

Safety and efficacy of losmapimod in facioscapulohumeral muscular dystrophy (ReDUX4): a randomised, double-blind, placebo-controlled phase 2b trial.

BACKGROUND: Facioscapulohumeral muscular dystrophy is a hereditary progressive myopathy caused by aberrant expression of the transcription factor DUX4 in skeletal muscle. No approved disease-modifying treatments are available for this disorder. We aimed to assess the safety and efficacy of losmapimod (a small molecule that inhibits p38α MAPK, a regulator of DUX4 expression, and p38ß MAPK) for the treatment of facioscapulohumeral muscular dystrophy. METHODS: We did a randomised, double-blind, placebo-controlled phase 2b trial at 17 neurology centres in Canada, France, Spain, and the USA. We included adults aged 18-65 years with type 1 facioscapulohumeral muscular dystrophy (ie, with loss of repression of DUX4 expression, as ascertained by genotyping), a Ricci clinical severity score of 2-4, and at least one skeletal muscle judged using MRI to be suitable for biopsy. Participants were randomly allocated (1:1) to either oral losmapimod (15 mg twice a day) or matching placebo for 48 weeks, via an interactive response technology system. The investigator, study staff, participants, sponsor, primary outcome assessors, and study monitor were masked to the treatment allocation until study closure. The primary endpoint was change from baseline to either week 16 or 36 in DUX4-driven gene expression in skeletal muscle biopsy samples, as measured by quantitative RT-PCR. The primary efficacy analysis was done in all participants who were randomly assigned and who had available data for assessment, according to the modified intention-to-treat principle. Safety and tolerability were assessed as secondary endpoints. This study is registered at ClinicalTrials.gov, number NCT04003974. The phase 2b trial is complete; an open-label extension is ongoing. FINDINGS: Between Aug 27, 2019, and Feb 27, 2020, 80 people were enrolled. 40 were randomly allocated to losmapimod and 40 to placebo. 54 (68%) participants were male and 26 (33%) were female, 70 (88%) were White, and mean age was 45·7 (SD 12·5) years. Least squares mean changes from baseline in DUX4-driven gene expression did not differ significantly between the losmapimod (0·83 [SE 0·61]) and placebo (0·40 [0·65]) groups (difference 0·43 [SE 0·56; 95% CI -1·04 to 1·89]; p=0·56). Losmapimod was well tolerated. 29 treatment-emergent adverse events (nine drug-related) were reported in the losmapimod group compared with 23 (two drug-related) in the placebo group. Two participants in the losmapimod group had serious adverse events that were deemed unrelated to losmapimod by the investigators (alcohol poisoning and suicide attempt; postoperative wound infection) compared with none in the placebo group. No treatment discontinuations due to adverse events occurred and no participants died during the study. INTERPRETATION: Although losmapimod did not significantly change DUX4-driven gene expression, it was associated with potential improvements in prespecified structural outcomes (muscle fat infiltration), functional outcomes (reachable workspace, a measure of shoulder girdle function), and patient-reported global impression of change compared with placebo. These findings have informed the design and choice of efficacy endpoints for a phase 3 study of losmapimod in adults with facioscapulohumeral muscular dystrophy. FUNDING: Fulcrum Therapeutics.

Clinical Spectrum and Prognosis in Patients With Acute Nutritional Axonal Neuropathy.

BACKGROUND AND OBJECTIVES: To describe the clinical, micronutrient, and electrophysiologic spectra and prognosis in patients with acute nutritional axonal neuropathy (ANAN). METHODS: Patients with ANAN were identified between 1999 and 2020 by a retrospective review of our EMG database and electronic health records and categorized on clinical and electrodiagnostic grounds, as pure sensory, sensorimotor, or pure motor; and by risk factor (alcohol use disorder, bariatric surgery, or anorexia). Laboratory abnormalities were recorded including thiamine, vitamin B6, B12, and E, folate, and copper. Ambulatory and neuropathic pain status at last follow-up were recorded. RESULTS: Of 40 patients with ANAN, 21 had alcohol use disorder, 10 were anorexic, and 9 had recently undergone bariatric surgery. Their neuropathy was pure sensory in 14 (7 with low thiamine), sensorimotor in 23 (8 with low thiamine), and pure motor in 3 (1 with low thiamine). Vitamin B1 was most commonly low (85%), followed by vitamin B6 (77%) and folate (50%). The risk factor and neuropathy type were not associated with a particular micronutrient deficiency. Of the 37 patients who were seen in follow-up, only 13 (35%) were walking independently, and only 8 (22%) were pain free at the last follow-up visit at a mean of 22 months (range 2-88 months) from onset. DISCUSSION: The spectrum of ANAN is wide, ranging from: (1) a pure sensory neuropathy with areflexia, limb and gait ataxia, neuropathic pain, and unevocable sensory responses to (2) a motor axonal neuropathy with low-amplitude motor responses without conduction slowing, block, or dispersion, and (3) a mixed sensorimotor axonal polyneuropathy. Specific micronutrient deficiencies or risk factors do not predict neuropathy subtype. The subgroup of patients with ANAN with documented thiamine deficiency also range from pure sensory to pure motor, and only a minority have Wernicke encephalopathy. We do not know whether coexistent micronutrient deficiencies may help explain the wide clinical spectrum of thiamine-deficient ANAN. The prognosis of ANAN is guarded due to residual neuropathic pain and slow recovery of independent ambulation. Therefore, early recognition of patients at risk is important.

Myotonic Dystrophy.

PURPOSE OF REVIEW: Myotonic dystrophy type 1 (DM1) and myotonic dystrophy type 2 (DM2) are genetic disorders affecting skeletal and smooth muscle, heart, brain, eyes, and other organs. The multisystem involvement and disease variability of myotonic dystrophy have presented challenges for clinical care and research. This article focuses on the diagnosis and management of the disease. In addition, recent advances in characterizing the diverse clinical manifestations and variability of the disease are discussed. RECENT FINDINGS: Studies of the multisystem involvement of myotonic dystrophy, including the most lethal cardiac and respiratory manifestations and their molecular underpinnings, expand our understanding of the myotonic dystrophy phenotype. Advances have been made in understanding the molecular mechanisms of both types of myotonic dystrophy, providing opportunities for developing targeted therapeutics, some of which have entered clinical trials in DM1. SUMMARY: Continued efforts focus on advancing our molecular and clinical understanding of DM1 and DM2. Accurately measuring and monitoring the diverse and variable clinical manifestations of myotonic dystrophy in clinic and in research is important to provide adequate care, prevent complications, and find treatments that improve symptoms and life quality.