Genetic determinants of disease severity in the myotonic dystrophy type 1 OPTIMISTIC cohort

Dyslexia and cognitive impairment in adult patients with myotonic dystrophy type 1: a clinical prospective analysis

BACKGROUND

Cognitive impairments in patients with myotonic dystrophy type 1 (DM1) have often been described, however, there are only few studies differentiating between partial performance disorders and mental retardation in common. This study focused on the evaluation of reading performance and the frequency of dyslexia in adult DM1 patients.

METHODS

We performed a prospective cohort study including genetically confirmed adult DM1 patients registered in the DM registry of Germany or the internal database of the Friedrich-Baur-Institute, Munich, Germany. For the assessment of the patients' reading and spelling performance, we used the standardized and validated test 'Salzburger Lese- und Rechtschreibtest' (SLRT II). The 'CFT-20 R Grundintelligenztest Skala 2' in revised ("R") version (CFT 20-R), determining the intelligence level, was appropriate to differentiate between dyslexia and general mental retardation. The diagnosis of dyslexia, the combined reading and spelling disorder, was based on the guidelines for diagnosis and therapy of children and adolescents with dyslexia 2015 (S3-guideline) providing (1) the criterion of the divergence from age level and (2) the criterion of IQ-divergence.

RESULTS

Fifty-seven DM1 patients participated in our study. Evaluating the reading performance, 16 patients fulfilled the divergence criteria of the age level and 2 patients the IQ-divergence criteria. In total, the diagnosis of a reading disorder was given in 18 DM1 patients (31.6 %). In 11 out of these 18 patients with a reading disorder, a relevant impairment of spelling performance was observed with at least three spelling errors. As there are no normative values for adults in spelling performance, we assume a combined reading disorder and dyslexia, in those 11 DM1 patients (19.3 %). Regarding the separate analyses of the test procedures, in the SLRT II the performance was below average in 40.4 % of all patients for 'word reading' and in 61.4 % of all patients for 'pseudoword reading'. There was a significant positive correlation between the CTG expansion size and a reading disorder (p=0.027). The average IQ of 17 examined DM1 patients was in the lower normal range (86.1 ± 19.1). 54.5 % of patients with reading disorder had a normal IQ.

CONCLUSION

The calculated prevalence of dyslexia in the DM1 study cohort was 19.3 % and thus considerably increased compared to the normal German population. As dyslexia is not equivalent to a general cognitive impairment, it is important not to miss dyslexic features in cognitive inconspicuous DM1 patients. Case-by-case one should consider a differential diagnostic approach, as individualized therapies can be offered to support dyslexic patients in their performance.

Stable Longitudinal Methylation Levels at the CpG Sites Flanking the CTG Repeat of DMPK in Patients with Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is an autosomal dominant multisystem disorder mainly characterized by gradual muscle loss, weakness, and delayed relaxation after muscle contraction. It is caused by an expanded CTG repeat in the 3′ UTR of DMPK, which is transcribed into a toxic gain-of-function mRNA that affects the splicing of a range of other genes. The repeat is unstable, with a bias towards expansions both in somatic cells and in the germline, which results in a tendency for earlier onset with each generation, as longer repeat lengths generally correlate with earlier onset. Previous studies have found hypermethylation in the regions flanking the repeat in congenital onset DM1 and in some patients with non-congenital DM1. We used pyrosequencing to investigate blood methylation levels in 68 patients with non-congenital DM1, compare the methylation levels between the blood and muscle, and assess whether methylation levels change over time in the blood. We found higher methylation levels in the blood of DM1 patients than in healthy controls and especially in the patients who had inherited the disease allele maternally. The methylation levels remained relatively stable over time and are a strong biomarker of the disease, as well as of the maternal inheritance of the disease.

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.

The Need for Establishing a Universal CTG Sizing Method in Myotonic Dystrophy Type 1

The number of cytosine-thymine-guanine (CTG) repeats (‘CTG expansion size’) in the 3′untranslated region (UTR) region of the dystrophia myotonica-protein kinase (DMPK) gene is a hallmark of myotonic dystrophy type 1 (DM1), which has been related to age of disease onset and clinical severity. However, accurate determination of CTG expansion size is challenging due to its characteristic instability. We compared five different approaches (heat pulse extension polymerase chain reaction [PCR], long PCR-Southern blot [with three different primers sets—1, 2 and 3] and small pool [SP]-PCR) to estimate CTG expansion size in the progenitor allele as well as the most abundant CTG expansion size, in 15 patients with DM1. Our results indicated variability between the methods (although we found no overall differences between long PCR 1 and 2 and SP-PCR, respectively). While keeping in mind the limited sample size of our patient cohort, SP-PCR appeared as the most suitable technique, with an inverse significant correlation found between CTG expansion size of the progenitor allele, as determined by this method, and age of disease onset (r = −0.734, p = 0.016). Yet, in light of the variability of the results obtained with the different methods, we propose that an international agreement is needed to determine which is the most suitable method for assessing CTG expansion size in DM1.

High Prevalence and Gender-Related Differences of Gastrointestinal Manifestations in a Cohort of DM1 Patients: A Perspective, Cross-Sectional Study

Myotonic dystrophy type 1 (DM1, MIM #160900), the most common muscular dystrophy among adults, is a multisystem disorder, which affects, besides the skeletal muscle, several other tissues and/or organs, including the gastrointestinal apparatus, with manifestations that frequently affect the quality of life of DM1 patients. So far, only few, mainly retrospective studies evaluated this specific topic in DM1, so we performed a perspective study, enrolling 61 DM1 patients who underwent an extensive diagnostic protocol, including administration of the Gastrointestinal Symptom Rating Scale (GSRS), a validated patient-reported questionnaire about GI symptoms, laboratory tests, liver US scan, and an intestinal permeability assay, in order to characterize frequency and assess correlations regarding specific gastrointestinal manifestations with demographic or other DM1-related features. Our results in our DM1 cohort confirm the high frequency of various gastrointestinal manifestations, with the most frequent being constipation (45.9%). γGT levels were pathologically increased in 65% of DM1 patients and GPT in 29.82%; liver ultrasound studies showed steatosis in 34.4% of patients. Significantly, 91.22% of DM1 patients showed signs of altered intestinal permeability at the specific assay. We documented a gender-related prevalence and severity of gastrointestinal manifestations in DM1 females compared to DM1 males, while males showed higher serum GPT and γGT levels than females. Correlation studies documented a direct correlation between severity of muscle weakness estimated by MIRS score and γGT and alkaline phosphatase levels, suggesting their potential use as biomarkers of muscle disease severity in DM1.

Activities of daily living in myotonic dystrophy type 1

OBJECTIVES

The objective of this cross-sectional, observational study was to investigate performance of activities of daily living in patients with myotonic dystrophy type 1 (DM1).

MATERIALS AND METHODS

Adults with genetically confirmed DM1 were recruited from Newcastle University (Newcastle upon Tyne, UK) and University College London Hospitals NHS Foundation Trust (London, UK). Data on activities of daily living were recorded through the DM1-ActivC (scale scores range between 0 and 100, where a higher/lower score indicates a higher/lower ability).

RESULTS

Our sample comprised 192 patients with DM1 (mean age: 46 years; 51% female). Patients reported most difficulties with running, carrying and putting down heavy objects, and standing on one leg, and least difficulties with eating soup, washing upper body, and taking a shower. Irrespective of the disease duration (mean: 20 years), most patients were able to perform basic and instrumental activities of daily living (eg personal hygiene and grooming, showering, eating, cleaning and shopping), with the exception of functional mobility/transfer tasks (eg walking uphill and running). The mean DM1-ActivC total score was estimated at 71 (95% CI: 68-74). Estimated progenitor cytosine-thymine-guanine repeat length and age explained 27% of the variance in DM1-ActivC total scores (P < .001).

CONCLUSIONS

We show that DM1 impairs performance of activities of daily living, in particular those requiring a high degree of muscle strength, stability and coordination. Yet, across the evolution of the disease, the majority of patients will still be able to independently perform most basic and instrumental activities of daily living.

Towards development of a statistical framework to evaluate myotonic dystrophy type 1 mRNA biomarkers in the context of a clinical trial

Myotonic dystrophy type 1 (DM1) is a rare genetic disorder, characterised by muscular dystrophy, myotonia, and other symptoms. DM1 is caused by the expansion of a CTG repeat in the 3'-untranslated region of DMPK. Longer CTG expansions are associated with greater symptom severity and earlier age at onset. The primary mechanism of pathogenesis is thought to be mediated by a gain of function of the CUG-containing RNA, that leads to trans-dysregulation of RNA metabolism of many other genes. Specifically, the alternative splicing (AS) and alternative polyadenylation (APA) of many genes is known to be disrupted. In the context of clinical trials of emerging DM1 treatments, it is important to be able to objectively quantify treatment efficacy at the level of molecular biomarkers. We show how previously described candidate mRNA biomarkers can be used to model an effective reduction in CTG length, using modern high-dimensional statistics (machine learning), and a blood and muscle mRNA microarray dataset. We show how this model could be used to detect treatment effects in the context of a clinical trial.

DM1 Phenotype Variability and Triplet Repeat Instability: Challenges in the Development of New Therapies

Myotonic dystrophy type 1 (DM1) is a complex neuromuscular disease caused by an unstable cytosine thymine guanine (CTG) repeat expansion in the DMPK gene. This disease is characterized by high clinical and genetic variability, leading to some difficulties in the diagnosis and prognosis of DM1. Better understanding the origin of this variability is important for developing new challenging therapies and, in particular, for progressing on the path of personalized treatments. Here, we reviewed CTG triplet repeat instability and its modifiers as an important source of phenotypic variability in patients with DM1.