Cognitive function and its relationship with brain structure in myotonic dystrophy type 1

Cognitive impairment, neuroimaging abnormalities, and their correlations in myotonic dystrophy: a comprehensive review

Myotonic dystrophy (DM) encompasses a spectrum of neuromuscular diseases characterized by myotonia, muscle weakness, and wasting. Recent research has led to the recognition of DM as a neurological disorder. Cognitive impairment is a central nervous system condition that has been observed in various forms of DM. Neuroimaging studies have increasingly linked DM to alterations in white matter (WM) integrity and highlighted the relationship between cognitive impairment and abnormalities in WM structure. This review aims to summarize investigations into cognitive impairment and brain abnormalities in individuals with DM and to elucidate the correlation between these factors and the potential underlying mechanisms contributing to these abnormalities.

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.

Longitudinal changes in white matter as measured with diffusion tensor imaging in adult-onset myotonic dystrophy type 1

Myotonic dystrophy type 1 is characterized by neuromuscular degeneration. Our objective was to compare change in white matter microstructure (fractional anisotropy, radial and axial diffusivity), and functional/clinical measures. Participants underwent yearly neuroimaging and neurocognitive assessments over three-years. Assessments encompassed full-scale intelligence, memory, language, visuospatial skills, attention, processing speed, and executive function, as well as clinical symptoms of muscle/motor function, apathy, and hypersomnolence. Mixed effects models were used to examine differences. 69 healthy adults (66.2% women) and 41 DM1 patients (70.7% women) provided 156 and 90 observations, respectively. There was a group by elapsed time interaction for cerebral white matter, where DM1 patients exhibited declines in white matter (all p<0.05). Likewise, DM1 patients either declined (motor), improved more slowly (intelligence), or remained stable (executive function) for functional outcomes. White matter was associated with functional performance; intelligence was predicted by axial (r = 0.832; p<0.01) and radial diffusivity (r = 0.291, p<0.05), and executive function was associated with anisotropy (r = 0.416, p<0.001), and diffusivity (axial: r = 0.237, p = 0.05 and radial: r = 0.300, p<0.05). Indices of white matter health are sensitive to progression in DM1. These results are important for clinical trial design, which utilize short intervals to establish treatment efficacy.

Longitudinal Changes in Neuropsychological Functioning in Japanese Patients with Myotonic Dystrophy Type 1: A Five Year Follow-Up Study

BACKGROUND

Myotonic dystrophy type 1 (DM1) is a form of muscular dystrophy that causes various symptoms, including those of the central nervous system. Some studies have reported cognitive decline in patients with DM1, although the available evidence is limited.

OBJECTIVE

This study aimed to describe longitudinal differences in neuropsychological function in patients with DM1.

METHODS

A total of 66 Japanese adult patients with DM1 were investigated using a neuropsychological battery to assess several cognitive domains, including memory, processing speed, and executive function. The patients underwent neuropsychological evaluation approximately five years after baseline (Times 1 and 2).

RESULTS

Thirty-eight patients underwent a second neuropsychological evaluation. The participants in the Time 2 evaluation were younger than those who did not participate in Time 2. Patients showed a decline in the Mini-Mental State Examination, Trail Making Test (TMT), Block Design, and Symbol Digit Modalities Test at Time 2 (P < 0.05). Age at Time 1 was associated with a decline in TMT-A and TMT-B scores (rho = 0.57 and 0.45, respectively).

CONCLUSION

These results suggest a cognitive decline in patients with DM1 and warrant further investigation into the possible effects of age-related changes.

Unravelling the impact of frontal lobe impairment for social dysfunction in myotonic dystrophy type 1

Myotonic dystrophy type 1 is an autosomal dominant multisystemic disorder affecting muscular and extra muscular systems, including the central nervous system. Cerebral involvement in myotonic dystrophy type 1 is associated with subtle cognitive and behavioural disorders, of major impact on socio-professional adaptation. The social dysfunction and its potential relation to frontal lobe neuropsychology remain under-evaluated in this pathology. The neuroanatomical network underpinning that disorder is yet to disentangle. Twenty-eight myotonic dystrophy type 1 adult patients (mean age: 46 years old) and 18 age and sex-matched healthy controls were included in the study. All patients performed an exhaustive neuropsychological assessment with a specific focus on frontal lobe neuropsychology (motivation, social cognition and executive functions). Among them, 18 myotonic dystrophy type 1 patients and 18 healthy controls had a brain MRI with T1 and T2 Flair sequences. Grey matter segmentation, Voxel-based morphometry and cortical thickness estimation were performed with Statistical Parametric Mapping Software SPM12 and Freesurfer software. Furthermore, T2 white matter lesions and subcortical structures were segmented with Automated Volumetry Software. Most patients showed significant impairment in executive frontal functions (auditory working memory, inhibition, contextualization and mental flexibility). Patients showed only minor difficulties in social cognition tests mostly in cognitive Theory of Mind, but with relative sparing of affective Theory of Mind and emotion recognition. Neuroimaging analysis revealed atrophy mostly in the parahippocampal and hippocampal regions and to a lesser extent in basal ganglia, regions involved in social navigation and mental flexibility, respectively. Social cognition scores were correlated with right parahippocampal gyrus atrophy. Social dysfunction in myotonic dystrophy type 1 might be a consequence of cognitive impairment regarding mental flexibility and social contextualization rather than a specific social cognition deficit such as emotion recognition. We suggest that both white matter lesions and grey matter disease could account for this social dysfunction, involving, in particular, the frontal-subcortical network and the hippocampal/arahippocampal regions, brain regions known, respectively, to integrate contextualization and social navigation.

Cognitive Dysfunction in Repeat Expansion Diseases: A Review

With the development of the sequencing technique, more than 40 repeat expansion diseases (REDs) have been identified during the past two decades. Moreover, the clinical features of these diseases show some commonality, and the nervous system, especially the cognitive function was affected in part by these diseases. However, the specific cognitive domains impaired in different diseases were inconsistent. Here, we survey literature on the cognitive consequences of the following disorders presenting cognitive dysfunction and summarizing the pathogenic genes, epidemiology, and different domains affected by these diseases. We found that the cognitive domains affected in neuronal intranuclear inclusion disease (NIID) were widespread including the executive function, memory, information processing speed, attention, visuospatial function, and language. Patients with C9ORF72-frontotemporal dementia (FTD) showed impairment in executive function, memory, language, and visuospatial function. While in Huntington's disease (HD), the executive function, memory, and information processing speed were affected, in the fragile X-associated tremor/ataxia syndrome (FXTAS), executive function, memory, information processing speed, and attention were impaired. Moreover, the spinocerebellar ataxias showed broad damage in almost all the cognitive domains except for the relatively intact language ability. Some other diseases with relatively rare clinical data also indicated cognitive dysfunction, such as myotonic dystrophy type 1 (DM1), progressive myoclonus epilepsy (PME), Friedreich ataxia (FRDA), Huntington disease like-2 (HDL2), and cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS). We drew a cognitive function landscape of the related REDs that might provide an aspect for differential diagnosis through cognitive domains and effective non-specific interventions for these diseases.

Brain Pathogenesis and Potential Therapeutic Strategies in Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is the most common muscular dystrophy that affects multiple systems including the muscle and heart. The mutant CTG expansion at the 3′-UTR of the DMPK gene causes the expression of toxic RNA that aggregate as nuclear foci. The foci then interfere with RNA-binding proteins, affecting hundreds of mis-spliced effector genes, leading to aberrant alternative splicing and loss of effector gene product functions, ultimately resulting in systemic disorders. In recent years, increasing clinical, imaging, and pathological evidence have indicated that DM1, though to a lesser extent, could also be recognized as true brain diseases, with more and more researchers dedicating to develop novel therapeutic tools dealing with it. In this review, we summarize the current advances in the pathogenesis and pathology of central nervous system (CNS) deficits in DM1, intervention measures currently being investigated are also highlighted, aiming to promote novel and cutting-edge therapeutic investigations.

Cognitive Deficits, Apathy, and Hypersomnolence Represent the Core Brain Symptoms of Adult-Onset Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 is the most common form of muscular dystrophy in adults, and is primarily characterized by muscle weakness and myotonia, yet some of the most disabling symptoms of the disease are cognitive and behavioral. Here we evaluated several of these non-motor symptoms from a cross-sectional time-point in one of the largest longitudinal studies to date, including full-scale intelligence quotient, depression, anxiety, apathy, sleep, and cerebral white matter fractional anisotropy in a group of 39 adult-onset myotonic dystrophy type 1 participants (27 female) compared to 79 unaffected control participants (46 female). We show that intelligence quotient was significantly associated with depression (P < 0.0001) and anxiety (P = 0.018), but not apathy (P < 0.058) or hypersomnolence (P = 0.266) in the DM1 group. When controlling for intelligence quotient, cerebral white matter fractional anisotropy was significantly associated with apathy (P = 0.042) and hypersomnolence (P = 0.034), but not depression (P = 0.679) or anxiety (P = 0.731) in the myotonic dystrophy type 1 group. Finally, we found that disease duration was significantly associated with apathy (P < 0.0001), hypersomnolence (P < 0.001), IQ (P = 0.038), and cerebral white matter fractional anisotropy (P < 0.001), but not depression (P = 0.271) or anxiety (P = 0.508). Our results support the hypothesis that cognitive deficits, hypersomnolence, and apathy, are due to the underlying neuropathology of myotonic dystrophy type 1, as measured by cerebral white matter fractional anisotropy and disease duration. Whereas elevated symptoms of depression and anxiety in myotonic dystrophy type 1 are secondary to the physical symptoms and the emotional stress of coping with a chronic and debilitating disease. Results from this work contribute to a better understanding of disease neuropathology and represent important therapeutic targets for clinical trials.

Neurocognitive Features of Motor Premanifest Individuals With Myotonic Dystrophy Type 1

Objective

The goal of the study was to identify brain and functional features associated with premanifest phases of adult-onset myotonic dystrophy type 1 (i.e., PreDM1).

Methods

This cross-sectional study included 68 healthy adults (mean age = 43.4 years, SD = 12.9), 13 individuals with PreDM1 (mean age: 47.4 years, SD = 16.3), and 37 individuals with manifest DM1 (mean age = 45.2 years, SD = 9.3). The primary outcome measures included fractional anisotropy (FA), motor measures (Muscle Impairment Rating Scale, Grooved Pegboard, Finger-Tapping Test, and grip force), general cognitive abilities (Wechsler Adult Intelligence Scales), sleep quality (Scales for Outcomes in Parkinson's Disease–Sleep), and apathy (Apathy Evaluation Scale).

Results

Individuals with PreDM1 exhibited an intermediate level of white matter FA abnormality, where whole-brain FA was lower relative to healthy controls (difference of the estimated marginal mean [EMM_difference] = 0.02, 95% confidence interval (CI) 0.01–0.03, p < 0.001), but the PreDM1 group had significantly higher FA than did individuals with manifest DM1 (EMM_difference = 0.02, 95% CI 0.009–0.03, p < 0.001). Individuals with PreDM1 exhibited reduced performance on the finger-tapping task relative to control peers (EMM_difference = 5.70, 95% CI 0.51–11.00, p = 0.03), but performance of the PreDM1 group was better than that of the manifest DM1 group (EMM_difference = 5.60, 95% CI 0.11–11.00, p = 0.05). Hypersomnolence in PreDM1 was intermediate between controls (EMM_difference = −1.70, 95% CI −3.10–0.35, p = 0.01) and manifest DM1 (EMM_difference = −2.10, 95% CI −3.50–0.60, p = 0.006).

Conclusions

Our findings highlight key CNS and functional deficits associated with PreDM1, offering insight in early disease course.

Central Nervous System Involvement as Outcome Measure for Clinical Trials Efficacy in Myotonic Dystrophy Type 1

Increasing evidences indicate that in Myotonic Dystrophy type 1 (DM1 or Steinert disease), an autosomal dominant multisystem disorder caused by a (CTG)n expansion in DMPK gene on chromosome 19q13. 3, is the most common form of inherited muscular dystrophy in adult patients with a global prevalence of 1/8000, and involvement of the central nervous system can be included within the core clinical manifestations of the disease. Variable in its severity and progression rate over time, likely due to the underlying causative molecular mechanisms; this component of the clinical picture presents with high heterogeneity involving cognitive and behavioral alterations, but also sensory-motor neural integration, and in any case, significantly contributing to the disease burden projected to either specific functional neuropsychological domains or quality of life as a whole. Principle manifestations include alterations of the frontal lobe function, which is more prominent in patients with an early onset, such as in congenital and childhood onset forms, here associated with severe intellectual disabilities, speech and language delay and reduced IQ-values, while in adult onset DM1 cognitive and neuropsychological findings are usually not so severe. Different methods to assess central nervous system involvement in DM1 have then recently been developed, these ranging from more classical psychometric and cognitive functional instruments to sophisticated psycophysic, neurophysiologic and especially computerized neuroimaging techniques, in order to better characterize this disease component, at the same time underlining the opportunity to consider it a suitable marker on which measuring putative effectiveness of therapeutic interventions. This is the reason why, as outlined in the conclusive section of this review, the Authors are lead to wonder, perhaps in a provocative and even paradoxical way to arise the question, whether or not the myologist, by now the popular figure in charge to care of a patient with the DM1, needs to remain himself a neurologist to better appreciate, evaluate and speculate on this important aspect of Steinert disease.

Encoding of facial expressions in individuals with adult-onset myotonic dystrophy type 1

Introduction: Emotional issues are often reported among individuals with myotonic dystrophy type 1 (DM1) and some studies have suggested that deficits in ability to quickly encode emotions may contribute to these problems. However, poor performance on emotion encoding tasks could also be explained by a more general cognitive deficit (Full Scale IQ [FSIQ]), rather than a specific deficit in emotional processing. Since individuals with DM1 are known to exhibit difficulties in general cognitive abilities, it is important to account for FSIQ when evaluating emotion encoding. The aim of this study was to compare emotion encoding abilities between individuals with and without DM1, while adjusting for the impact of general cognitive abilities (FSIQ). Methods: The sample included 35 individuals with adult-onset DM1 and 54 unaffected adults who completed assessments of emotion encoding abilities (Ekman faces test) and general cognitive abilities (Wechsler Adult Intelligence Scale-IV). Performance on the emotion encoding task was operationalized as proportion correct and response time. Group differences in proportion correct were evaluated with generalized linear regression, while linear regression models were used to determine the effect of group on response time. Models were adjusted for age, sex, and FSIQ. The false discovery rate (FDR) was applied to control false positives due to multiple comparisons (p_fdr ). Results: No significant group differences were observed for emotion encoding abilities (all p_fdr > 0.13). FSIQ was significantly associated with proportion correct and with response time (all p_fdr < 0.05). Conclusions: Emotion encoding appears intact in individuals with DM1 and variation in the ability to encode facial expressions was associated with FSIQ. Further research is required to address the relationship between general cognitive abilities and emotion encoding abilities among DM1 patients.

Variant repeats within the DMPK CTG expansion protect function in myotonic dystrophy type 1

Objective

We tested the hypothesis that variant repeat interruptions (RIs) within the DMPK CTG repeat tract lead to milder symptoms compared with pure repeats (PRs) in myotonic dystrophy type 1 (DM1).

Methods

We evaluated motor, neurocognitive, and behavioral outcomes in a group of 6 participants with DM1 with RI compared with a case-matched sample of 12 participants with DM1 with PR and a case-matched sample of 12 unaffected healthy comparison participants (UA).

Results

In every measure, the RI participants were intermediate between UA and PR participants. For muscle strength, the RI group was significantly less impaired than the PR group. For measures of Full Scale IQ, depression, and sleepiness, all 3 groups were significantly different from each other with UA > RI > PR in order of impairment. The RI group was different from unaffected, but not significantly different from PR (UA > RI = PR) in apathy and working memory. Finally, in finger tapping and processing speed, RI did not differ from UA comparisons, but PR had significantly lower scores than the UA comparisons (UA = RI > PR).

Conclusions

Our results support the notion that patients affected by DM1 with RI demonstrate a milder phenotype with the same pattern of deficits as those with PR indicating a similar disease process.