DM1 Transgenic Mice Exhibit Abnormal Neurotransmitter Homeostasis and Synaptic Plasticity in Association with RNA Foci and Mis-Splicing in the Hippocampus.

Myotonic dystrophy type 1 (DM1) is a severe neuromuscular disease mediated by a toxic gain of function of mutant RNAs. The neuropsychological manifestations affect multiple domains of cognition and behavior, but their etiology remains elusive. Transgenic DMSXL mice carry the DM1 mutation, show behavioral abnormalities, and express low levels of GLT1, a critical regulator of glutamate concentration in the synaptic cleft. However, the impact of glutamate homeostasis on neurotransmission in DM1 remains unknown. We confirmed reduced glutamate uptake in the DMSXL hippocampus. Patch clamp recordings in hippocampal slices revealed increased amplitude of tonic glutamate currents in DMSXL CA1 pyramidal neurons and DG granule cells, likely mediated by higher levels of ambient glutamate. Unexpectedly, extracellular GABA levels and tonic current were also elevated in DMSXL mice. Finally, we found evidence of synaptic dysfunction in DMSXL mice, suggestive of abnormal short-term plasticity, illustrated by an altered LTP time course in DG and in CA1. Synaptic dysfunction was accompanied by RNA foci accumulation in localized areas of the hippocampus and by the mis-splicing of candidate genes with relevant functions in neurotransmission. Molecular and functional changes triggered by toxic RNA may induce synaptic abnormalities in restricted brain areas that favor neuronal dysfunction.

Cerebral ventriculomegaly in myotonic dystrophy type 1: normal pressure hydrocephalus-like appearances on magnetic resonance imaging.

BACKGROUND: Cerebral ventriculomegaly is an abnormal feature characteristic of myotonic dystrophy type 1 (DM1). This retrospective study investigated the morphologic changes accompanied by ventriculomegaly in DM1 on brain MRI. METHODS: One hundred and twelve adult patients with DM1 and 50 sex- and age-matched controls were assessed. The imaging characteristics for evaluations included the z-Evans Index (ventriculomegaly), callosal angle (CA), enlarged perivascular spaces in the centrum semiovale (CS-EPVS), temporo-polar white matter lesion (WML) on 3D fluid-attenuated inversion recovery (FLAIR), disproportionately enlarged subarachnoid-space hydrocephalus (DESH), and pathological brain atrophy. The "z-Evans Index" was defined as the maximum z-axial length of the frontal horns to the maximum cranial z-axial length. To determine the imaging characteristics and genetic information (CTG repeat numbers) that were associated with the z-Evans Index, we used binominal logistic regression analyses. RESULTS: The z-Evans Index was significantly larger in the patients than in the controls (0.30 ± 0.05 vs. 0.24 ± 0.02; p < 0.01). The z-Evans Index was independently associated with the callosal angle (p < 0.01) and pathological brain atrophy (p < 0.01) but not with age, gender, CTG repeat numbers, or CS-EPVS. Of the 34 patients older than 49 years, 7 (20.6%) were considered to have DESH. CONCLUSIONS: Our MRI study revealed a normal pressure hydrocephalus (NPH)-like appearance as a morphologic finding accompanied by ventriculomegaly in DM1 that tends to occur in elderly patients.

Multifocal Noninvasive Magnetic Stimulation of the Primary Motor Cortex in Type 1 Myotonic Dystrophy -A Proof of Concept Pilot Study.

BACKGROUND: Repeated neuromuscular electrical stimulation in type 1 Myotonic Dystrophy (DM1) has previously been shown to cause an increase in strength and a decrease in hyperexcitability of the tibialis anterior muscle. OBJECTIVE: In this proof-of-principle study our objective was to test the hypothesis that noninvasive repetitive transcranial magnetic stimulation of the primary motor cortex (M1) with a new portable wearable multifocal stimulator causes improvement in muscle function in DM1 patients. METHODS: We performed repetitive stimulation of M1, localized by magnetic resonance imaging, with a newly developed Transcranial Rotating Permanent Magnet Stimulator (TRPMS). Using a randomized within-patient placebo-controlled double-blind TRPMS protocol, we performed unilateral active stimulation along with contralateral sham stimulation every weekday for two weeks in 6 adults. Methods for evaluation of muscle function involved electromyography (EMG), hand dynamometry and clinical assessment using the Medical Research Council scale. RESULTS: All participants tolerated the treatment well. While there were no significant changes clinically, EMG showed significant improvement in nerve stimulus-evoked compound muscle action potential amplitude of the first dorsal interosseous muscle and a similar but non-significant trend in the trapezius muscle, after a short exercise test, with active but not sham stimulation. CONCLUSIONS: We conclude that two-week repeated multifocal cortical stimulation with a new wearable transcranial magnetic stimulator can be safely conducted in DM1 patients to investigate potential improvement of muscle strength and activity. The results obtained, if confirmed and extended by future safety and efficacy trials with larger patient samples, could offer a potential supportive TRPMS treatment in DM1.

Endocrine Dysfunction in Patients With Myotonic Dystrophy.

Myotonic dystrophy is a dominantly inherited multisystem disorder that results from increased CTG repeats in the 3' region of the myotonic dystrophy protein kinase gene (DMPK). The mutant DMPK mRNA remains in the nucleus and sequesters RNA-binding proteins, including regulators of mRNA splicing. Myotonic dystrophy is characterized by a highly variable phenotype that includes muscle weakness and myotonia, and the disorder may affect the function of many endocrine glands. DMPK mRNA is expressed in muscle, testis, liver, pituitary, thyroid, and bone; the mutated form leads to disruption of meiosis and an increase in fetal insulin receptor-A relative to adult insulin receptor-B, resulting in adult primary testicular failure and insulin resistance predisposing to diabetes, respectively. Patients with myotonic dystrophy are also at increased risk for hyperlipidemia, nonalcoholic fatty liver disease, erectile dysfunction, benign and malignant thyroid nodules, bone fractures, miscarriage, preterm delivery, and failed labor during delivery. Circulating parathyroid hormone and adrenocorticotropic hormone levels may be elevated, but the mechanisms for these associations are unclear. This review summarizes what is known about endocrine dysfunction in individuals with myotonic dystrophy.

What Happened with Muscle Force, Dynamic Stability And Falls? A 10-Year Longitudinal Follow-Up in Adults with Myotonic Dystrophy Type 1.

BACKGROUND: Individuals with myotonic dystrophy type 1 (DM1) are known to stumble and fall, but knowledge is scarce regarding dynamic stability in this disorder. OBJECTIVE: To describe disease progress regarding muscle force, dynamic stability and patient reported unintentional falls during a ten-year period, in individuals with DM1. METHODS: Quantification of isometric muscle force in four leg muscle groups and assessment of Timed 10-meter-walk in maximum speed (T10max), Timed Up&Go (TUG) and Step test (STEP) were performed at three occasions in a DM1 cohort, together with self-reported falls. RESULTS: Thirty-four people (m/f:11/23, age: 50.2 + /-9.4) participated. The muscle force loss after ten years was large in the distal ankle muscles. A steeper force decrease was seen in most muscles between year five and ten compared to the former five-year period. Males reported more falls than females, 91% vs 35% had fallen last year. A positive correlation, ρ= 0.633, p < 0.001, was shown between walking time (T10max) and number of falls. Frequent fallers were only seen among those with slower walk (T10max > 10seconds), and fewer steps in the STEP test (STEP≤5 steps). CONCLUSIONS: A diminishing leg muscle strength and worse dynamic stability were seen in the group, with a steeper decrease in the latter five years. Weak ankle dorsiflexors, a slower walk and difficulties to lift the forefoot were related to frequent falls.

A case report of malignant hyperthermia in a patient with myotonic dystrophy type I: A CARE-compliant article.

RATIONALE: Several hereditary myopathies that can predispose to malignant hyperthermia (MH) are reported. However, the risk of MH in myotonic dystrophy type I (DM1) has been suggested equal to general population, although the evidence is limited to only a few case reports. PATIENT CONCERNS: We encountered a rare case of MH during anesthesia induction with sevoflurane in a male adolescent with previously undiagnosed DM1. DIAGNOSES: After the event, genetic testing revealed the presence of a previously unknown heterozygous missense mutation in ryanodine receptor 1 (RYR1) associated with MH (c.6898T > C; p.ser2300Pro). Concomitantly, the patient was diagnosed with DM1 with abnormal cytosine-thymine-guanine triplet expansion in the DMPK gene. INTERVENTIONS: Dantrolene was administered to treat the hypermetabolic manifestations in 20 minutes after the identification of MH. OUTCOMES: The patient was successfully treated and discharged without any complications. Laboratory abnormalities were recovered to baseline at postoperative 4 days. LESSONS: The authors suggest that possible MH susceptibility in DM1 patients may be refocused. Genetic testing can be a screening tool for MH susceptibility in these population, prior to receiving general anesthesia.

The alternative initiation factor eIF2A plays key role in RAN translation of myotonic dystrophy type 2 CCUG•CAGG repeats.

Repeat-associated non-ATG (RAN) proteins have been reported in 11 microsatellite expansion disorders but the factors that allow RAN translation to occur and the effects of different repeat motifs and alternative AUG-like initiation codons are unclear. We studied the mechanisms of RAN translation across myotonic dystrophy type 2 (DM2) expansion transcripts with (CCUG) or without (CAGG) efficient alternative AUG-like codons. To better understand how DM2 LPAC and QAGR RAN proteins are expressed, we generated a series of CRISPR/Cas9-edited HEK293T cell lines. We show that LPAC and QAGR RAN protein levels are reduced in protein kinase R (PKR)-/- and PKR-like endoplasmic reticulum kinase (PERK)-/- cells, with more substantial reductions of CAGG-encoded QAGR in PKR-/- cells. Experiments using mutant eIF2α-S51A HEK293T cells show that p-eIF2α is required for QAGR production. In contrast, LPAC levels were only partially reduced in these cells, suggesting that both non-AUG and close-cognate initiation occur across CCUG RNAs. Overexpression of the alternative initiation factor eIF2A increases LPAC and QAGR protein levels but, notably, has a much larger effect on QAGR expressed from CAGG-expansion RNAs that lack efficient close-cognate codons. The effects of eIF2A on increasing LPAC are consistent with previous reports that eIF2A affects CUG-initiation translation. The observation that eIF2A also increases QAGR proteins is novel because CAGG expansion transcripts do not contain CUG or similarly efficient close-cognate AUG-like codons. For QAGR but not LPAC, the eIF2A-dependent increases are not seen when p-eIF2α is blocked. These data highlight the differential regulation of DM2 RAN proteins and eIF2A as a potential therapeutic target for DM2 and other RAN diseases.

Isokinetic strength and degeneration of lower extremity muscles in patients with myotonic dystrophy; an MRI study.

Our aim was to determine isokinetic strength and degeneration of lower extremity muscles in patients with Myotonic Dystrophy (DM1). In 19 patients with DM1 and 19 matched controls, strength measured by isokinetic dynamometry was expressed as percentage of expected strength (ePct), adjusted for age, height, weight and gender. MRI of the hip, thigh and calf muscles were obtained. Fat fraction (FF), mean contractile cross-sectional area (cCSA) and specific strength (Nm/cm2) were calculated. Patients' ankle plantar flexors, knee flexors and extensors had higher FF (Δ: 0.08 - 0.42) and lower cCSA (Δ: 3.2 -17.1 cm2) compared to controls (p ≤ 0.005). EPct (Δ: 19.5 - 41.6%) and specific strength (Δ: 0.27 - 0.96 Nm/cm2) were lower in the majority of patients muscle groups (p˂0.05). Close correlations were found for patients when relating ePct to; FF for plantar flexors (R2=0.742, p<0.001) and knee extensors (R2=0.732, p<0.001), cCSA for plantar flexors (R2=0.696, p<0.001) and knee extensors (R2=0.633, p<0.001), and specific strength for dorsal flexors (ρ=0.855, p = 0.008). In conclusion, patients had weaker lower extremity muscles with higher FF, lower cCSA and specific strength compared to controls. Muscle degeneration determined by quantitative MRI strongly correlated to strength supporting its feasibility to quantify muscle dysfunction in DM1.

Prevalence of atrial fibrillation in myotonic dystrophy type 1: A systematic review.

Cardiac involvement is recorded in about 80% of patients affected by myotonic dystrophy type 1 (DM1). The prevalence of cardiac conduction abnormalities is well described. Data regarding the prevalence of atrial fibrillation (AF) are still conflicting. The primary objective of this review was to assess the prevalence of AF in DM1. The secondary aim was to examine the association of clinical features with AF, to detect predisposing and/or influencing prognosis factors. A systematic search was developed in MEDLINE, EMBASE, Cochrane Register of Controlled Trials and Web of Science databases, to identify original reports between January 1, 2002 and January 30, 2020, assessing the prevalence of AF in DM1 population. Retrospective/prospective cohort studies and case series describing the prevalence of atrial fibrillation evaluated by periodic electrocardiogram (ECG) and/or ECG Holter 24 h, external loop recording (ELR) and implantable devices interrogation in DM1 patients were included. Case reports, simple reviews, commentaries and editorials were excluded. Thirteen reports fulfilled eligibility criteria and were included in our systematic review. According to the results from all the evaluated studies, the mean prevalence of AF in DM1 patients was 10.9% (n = 404) in 3677 DM1 patients. Male sex, conduction defects, echocardiographic findings of prolonged atrial electromechanical delay seem to be strongly associated with atrial fibrillation, representing factors favoring its onset. DM1 patients who develop AF seem to have a higher risk of cardiovascular and non-cardiovascular death. Further studies are needed to assess the prevalence of AF in DM1 patients and to investigate ECG abnormalities and other clinical features associated with this condition.

iPSC-derived cardiomyocytes from patients with myotonic dystrophy type 1 have abnormal ion channel functions and slower conduction velocities.

Cardiac complications such as electrical abnormalities including conduction delays and arrhythmias are the main cause of death in individuals with Myotonic Dystrophy type 1 (DM1). We developed a disease model using iPSC-derived cardiomyocytes (iPSC-CMs) from a healthy individual and two DM1 patients with different CTG repeats lengths and clinical history (DM1-1300 and DM1-300). We confirmed the presence of toxic RNA foci and mis-spliced MBNL1/2 transcripts in DM1 iPSC-CMs. In DM1-1300, we identified a switch in the cardiac sodium channel SCN5A from the adult to the neonatal isoform. The down-regulation of adult SCN5A isoforms is consistent with a shift in the sodium current activation to depolarized potentials observed in DM1-1300. L-type calcium current density was higher in iPSC-CMs from DM1-1300, which is correlated with the overexpression of the CaV1.2 transcript and proteins. Importantly, INa and ICaL dysfunctions resulted in prolonged action potentials duration, slower velocities, and decreased overshoots. Optical mapping analysis revealed a slower conduction velocity in DM1-1300 iPSC-CM monolayers. In conclusion, our data revealed two distinct ions channels perturbations in DM1 iPSC-CM from the patient with cardiac dysfunction, one affecting Na+ channels and one affecting Ca2+ channels. Both have an impact on cardiac APs and ultimately on heart conduction.

Quantitative muscle MRI as a sensitive marker of early muscle pathology in myotonic dystrophy type 1.

BACKGROUND: Quantitative muscle MRI as a sensitive marker of early muscle pathology and disease progression in adult-onset myotonic dystrophy type 1. The utility of muscle MRI as a marker of muscle pathology and disease progression in adult-onset myotonic dystrophy type 1 (DM1) was evaluated. METHODS: This prospective, longitudinal study included 67 observations from 36 DM1 patients (50% female), and 92 observations from 49 healthy adults (49% female). Lower-leg 3T magnetic resonance imaging (MRI) scans were acquired. Volume and fat fraction (FF) were estimated using a three-point Dixon method, and T2-relaxometry was determined using a multi-echo spin-echo sequence. Muscles were segmented automatically. Mixed linear models were conducted to determine group differences across muscles and image modality, accounting for age, sex, and repeated observations. Differences in rate of change in volume, T2-relaxometry, and FF were also determined with mixed linear regression that included a group by elapsed time interaction. RESULTS: Compared with healthy adults, DM1 patients exhibited reduced volume of the tibialis anterior, soleus, and gastrocnemius (GAS) (all, P < .05). T2-relaxometry and FF were increased across all calf muscles in DM1 compared to controls. (all, P < .01). Signs of muscle pathology, including reduced volume, and increased T2-relaxometry and FF were already noted in DM1 patients who did not exhibit clinical motor symptoms of DM1. As a group, DM1 patients exhibited a more rapid change than did controls in tibialis posterior volume (P = .05) and GAS T2-relaxometry (P = .03) and FF (P = .06). CONCLUSIONS: Muscle MRI renders sensitive, early markers of muscle pathology and disease progression in DM1. T2 relaxometry may be particularly sensitive to early muscle changes related to DM1.

Opioid use may be associated with postoperative complications in myotonic dystrophy type 1 with high-grade muscular impairment.

Individuals with myotonic dystrophy type 1 (DM1) reportedly have a higher risk of postoperative complications than those without DM1; however, factors related to perioperative complications in DM1 patients remain unclear. We aimed to identify the risk factors that may be associated with postoperative complications in DM1 patients. We reviewed medical records of 256 patients with DM1 from 1998 to 2018, among whom 42 (16.4%) had previously undergone 51 surgeries under general and regional anaesthesia. Among the 42 patients, 11 (21.5%) had 13 postoperative complications including respiratory complications, sustained hypotension, wound infection and dehiscence, artery thrombosis and occlusion, and delayed recovery from anaesthesia. There were significant inter-group differences between the non-complicated and complicated groups considering the following parameters: high-grade (≥ 3) muscular impairment rating scale (MIRS), extubation time, postoperative opioid use, and hospital length of stay. Furthermore, univariate analysis revealed that an MIRS score ≥ 3 (odds ratio [OR] 9.346, confidence interval [CI] 1.761-49.595, p = 0.009) and postoperative opioid use (OR 8.000, CI 1.772-36.127, p = 0.007) were the only statistically significant factors. Therefore, clinicians should be cautious in administering opioids, particularly in patients with a high-grade MIRS score during the perioperative period.

Clinical characteristics of metabolic associated fatty liver disease (MAFLD) in subjects with myotonic dystrophy type 1 (DM1).

BACKGROUND: Myotonic dystrophy type 1 (DM1) is a rare inherited neuromuscular disease associated with insulin resistance, and its association with metabolically associated fatty liver disease (MAFLD) has never been explored in prospective studies. The aim of this study was to assess the clinical features of MAFLD in DM1 patients. METHODS: We investigated the prevalence and the diagnostic features of MAFLD in a cohort of 29 outpatient fully characterized DM1 patients; afterward, we compared the selected cohort of DM1-MAFLD individuals with a propensity-matched cohort of non-DM1-MAFLD RESULTS: 13/29 (44.83%) DM1 patients received a clinical diagnosis of MAFLD. Compared to DM1 patients with normal liver, DM1-MAFLD individuals showed a higher male prevalence (p = 0.008), BMI (p = 0.014), HOMA score (p = 0.012), and GGT levels (p = 0.050). The statistical comparison showed that the DM1-MAFLD group had a more severe MAFLD according to the FIB4 score than non-DM1-MAFLD patients. This association of a more severe form of liver disease with DM1 remained significant after logistic regression analysis (OR: 6.12, 95% CI 1.44- 26.55).

Effect of exercise training on functional capacity and body composition in myotonic dystrophy type 2 patients.

BACKGROUND: Myotonic dystrophy type 2 (DM2) is a neuromuscular disorder characterized by myotonia and muscle weakness, with no medical treatment to prevent a decline in decline. It is unknown whether exercise training is effective in DM2. The aim of this study was to investigate the effect of exercise training on functional capacity and body composition in these patients. METHODS: Body composition and functional capacity were evaluated at the beginning (T1) and end (T2) of a 12 wk control period, and again after 16 wk of exercise training (T3) in 10 patients. RESULTS: No changes were recorded after the control period. Handgrip strength, 5× sit to stand, timed up and go, 6 min walk distance, lean body mass (LBM), and bone mineral density (BMD) increased while arterial pressure decreased after training. CONCLUSIONS: These results suggest that supervised exercise training improves functional capacity, LBM, and BMD in ambulatory DM2 patients.

Mexiletine in Myotonic Dystrophy Type 1: A Randomized, Double-Blind, Placebo-Controlled Trial.

OBJECTIVE: To assess mexiletine's long-term safety and effect on 6-minute walk distance in a well-defined cohort of patients with myotonic dystrophy type 1 (DM1). METHODS: We performed a randomized, double-blind, placebo-controlled trial of mexiletine (150 mg 3 times daily) to evaluate its efficacy and safety in a homogenous cohort of adult ambulatory patients with DM1. The primary outcome was change in 6-minute walk distance at 6 months. Secondary outcomes included changes in hand grip myotonia, strength, swallowing, forced vital capacity, lean muscle mass, Myotonic Dystrophy Health Index scores, and 24-hour Holter and ECG results at 3 and 6 months. RESULTS: Forty-two participants were randomized and 40 completed the 6-month follow-up (n = 20 in both groups). No significant effects of mexiletine were observed on 6-minute walk distance, but hand grip myotonia was improved with mexiletine treatment. There were no differences between the mexiletine and placebo groups with respect to the frequency or type of adverse events. Changes in PR, QRS, and QTc intervals were similar in mexiletine- and placebo-treated participants. CONCLUSIONS: There was no benefit of mexiletine on 6-minute walk distance at 6 months. Although mexiletine had a sustained positive effect on objectively measured hand grip myotonia, this was not seen in measures reflecting participants' perceptions of their myotonia. No effects of mexiletine on cardiac conduction measures were seen over the 6-month follow-up period. CLASSIFICATION OF EVIDENCE: This study provides Class I evidence that for ambulatory patients with DM1, mexiletine does not significantly change 6-minute walk distance at 6 months.

Cognitive Decline and White Matter Integrity Degradation in Myotonic Dystrophy Type I.

BACKGROUND AND PURPOSE: Myotonic Dystrophy Type I (DM1) is a neurodegenerative, genetic, and multisystemic disorder with a large variety of symptoms due to a CTG trinucleotide expansion located on Dystrophia Myotonica Protein Kinase (DMPK) gene. Previous reports have shown cognitive deterioration in these patients. Given that white matter (WM) degradation has also been reported in DM1 patients, here we explored if alterations in the cognitive profile of DM1 patients could be related to the deterioration of WM. METHODS: A total of 22 classic DM1 patients with age range (18-56 years) and 22 matched healthy control subjects were neuropsychological evaluated by the Cambridge Neuropsychological Test Automated (CANTAB). Patients were evaluated with the Muscular Impairment Rating Scale (MIRS). We then evaluated the cerebral WM integrity using the Fractional Anisotropy (FA) index obtained from the Diffusion Tensor Imaging (DTI) data acquired with a 3T MR scanner. RESULTS: DM1 patients showed generalized reduction of WM integrity across the brain. Similarly, patients' neuropsychological evaluation showed significant deficits in memory and problem-solving tasks. Correlation analyses showed a significant correlation between FA deterioration at frontal, temporomedial, and parietal lobes and delayed matched to sample deficits. CONCLUSIONS: Our results suggest that despite the pervasive WM integrity loss in DM1 disorder, specific memory impairments can be associated to discreet areas of WM deterioration in these patients.

12-Month progression of motor and functional outcomes in congenital myotonic dystrophy.

BACKGROUND: We aim to describe 12-mo functional and motor outcome performance in a cohort of participants with congenital myotonic dystrophy (CDM). METHODS: CDM participants performed the 6 Minute Walk Test (6MWT), 10 Meter Run, 4 Stair Climb, Grip Strength, and Lip Force at baseline and 12-mo visits. Parents completed the Vineland Adaptive Behavior Scale. RESULTS: Forty-seven participants, aged 0 to 13 y old, with CDM were enrolled. 6MWT, 10 Meter Run, and 4 Stair Climb were completed in >85% of eligible participants. The only significant difference between mean baseline and 12-mo performance was an improvement in 6MWT in children 3-6 y old (P = .008). This age group also had the largest mean % improvement in performance in all other timed functional testing. In children >7 y, the slope of change on timed functional tests decreased or plateaued, with further reductions in performance in children ≥10 y. Participants with CTG repeat lengths <500 did not perform differently than those with repeat lengths >1000. CONCLUSIONS: The 6MWT, 10 Meter Run, and 4 Stair Climb were the most feasible measures. Our findings are consistent with the clinical profile and prior cross-sectional data, helping to establish reasonable expectations of functional trajectories in this population as well as identifying points in which therapeutic interventions may be best studied. Further study of outcomes in children >10 y old and <3 y is warranted, but this new information will assist planning of clinical trials in the CDM population.

Predictors of prognosis in type 1 myotonic dystrophy (DM1): longitudinal 18-years experience from a single center.

The aim of the study was to identify possible predictors of neurological worsening and need of non-invasive ventilation (NIV) in individuals affected by myotonic dystrophy type 1 (DM1), the most common form of adult-onset muscular dystrophy. METHODS: A retrospective observational cohort study was undertaken. Thirty-three patients with genetic diagnosis of DM1 were followed at our Neuromuscular unit in Modena. Abnormal trinucleotide repeat (CTG) expansion of dystrophy protein kinase gene (MDPK) on chromosome 19q 13.3 was the prerequisite for inclusion. The number of CTG repeats was determined. All the participants were older than 14 at the time of enrolment, therefore they could be included into the juvenile or adult form of the disease. Participants were neurologically evaluated every 6-8 months up to 18 years. Neurological impairment was assessed by Muscular Impairment Rating (MIRS), Medical Research Council (MRC), and modified Rankin (mRS) scales. The independent variables considered for prognosis were age at first evaluation, duration of the disease, CTG repeat number, gender, and presence of cardiac and vascular morbidities.Male patients were 51.5% and female patients 48.5%. Sixteen patients were younger than the mean age of 30.1 years, while the remaining 17 were up to 65. Twelve subjects (36.4%) underwent NIV before the end of follow-up. Muscle force and disability scores showed statistically significant deterioration (p < 0.001) during follow-up. The worsening was significantly higher among patients carrying higher number of CTG repeats and of younger age. The presence of cardio-vascular involvement has significant impact on neurological and respiratory progression.Neurological worsening is predicted by CTG expansion size, young age and presence of cardio-vascular morbidities.