Myotonic dystrophy and progressive cognitive decline: a common condition or two separate problems?

Disease awareness in myotonic dystrophy type 1: an observational cross-sectional study

BACKGROUND

Myotonic dystrophy type 1 (Steinert's disease or DM1), the most common form of autosomal dominant muscular dystrophy in adults, is a multisystem disorder, affecting skeletal muscle as well as eyes, heart, gastrointestinal tract, endocrine system, and central nervous system, finally responsible of increasing disabilities and secondary social consequences. To date, DM1-related brain involvement represents a challenging field of research. It is well known that DM1 patients frequently present neuropsychological disturbances and psychiatric comorbidities among which reduced awareness of disease burden and its progression, also defined as anosognosia, is common in clinical practice, this leading to secondary misattribution of symptoms, delay in timely diagnostic procedures and low compliance to treatment.

METHODS

Here we present an observational cross sectional study in which disease-related cognitive dysfunctions and quality of life were assessed by a protocol finally designed to estimate the prevalence of disease awareness in a sample of 65 adult-onset DM1 patients.

RESULTS

Our analysis showed that in DM1 patients several cognitive functions, including executive and mnesic domains with visuo-spatial involvement, were affected. The assessment of anosognosia revealed that a high percentage (51.6%) of DM1 subjects was disease unaware. The reduced illness awareness occurs across different physical and life domains, and it appears more prominent in Activities and Independence domains investigated by the Individualized Neuromuscular Quality Of Life (INQoL) questionnaire. Moreover, the unawareness resulted significantly related (at p <0.05 and p < 0.01) to the performance failure in cognitive tests, specifically in the domains of visuo-spatial memory, cognitive flexibility and conceptualization.

CONCLUSIONS

The obtained data confirm, by a systematic analysis, what's the common clinical perceiving of disease unawareness in Steinert's disease, this related to the already known cognitive-behavioural impairment of frontal type in affected patients. We believe that a deep knowledge of this aspect will be useful for medical practice in the management of patients with DM1, also for guidance in occupational and social interventions, definition of outcome measures and in preparation of trial readiness.

Toward understanding cognitive impairment in patients with myotonic dystrophy type 1

Cognitive dysfunction and sleep disruption are two frequent but underestimated features of adult onset myotonic dystrophy type 1 (MD1). In order to investigate the MD1 cognitive profile and its relationship with sleep disruption, 23 patients with genetically proved MD1 (mild-moderate in severity) underwent neuropsychological (nps) and polysomnography assessment. Patients scored lower than controls on almost all nps tests but cognitive impairments were mostly observed in executive functions (z-score = -2.14), with complex attention (z-score = -1.04), memory (z-score = -0.65), constructions (z-score = -1.29), and reasoning (z-score = -0.75) being slightly affected. Moderate-severe sleep apnea (apnea-hypopnea index [AHI] > or =15) was very frequent with most of the apneas being of the obstructive type. However, we found hardly any evidence of association between subjective, objective sleep parameters, and nps performance (p > .001). Thus, in our cohort of 23 adult MD1 patients, mild cognitive dysfunction, which is mostly related to the dysfunction of frontal association cortex and its underlying neural networks, does not seem to be significantly influenced by sleep disruption, which is mainly caused by obstructive apnea events.

A 5-year follow-up study of an atypical case of myotonic dystrophy

This study presents 5-year follow-up data on NG, a woman with adult onset myotonic dystrophy and progressive cognitive decline who was first described by Wilson et al. The extent of the cognitive impairment is atypical of symptom-onset in adulthood and of paternal inheritance, both of which apply to this case. Together, the present and earlier studies report the results of regular neuropsychological assessments over a 16-year period. Severe impairment in executive functioning, episodic and semantic memory were apparent early in the history, while visuospatial skills and working memory were only mildly impaired after 16 years of follow-up. There was also a progressive dyslexia, initially characterized by the regularization errors typical of surface dyslexia, but subsequently dominated by visual/phonological reading errors. This pattern of impairment is not typical of myotonic dystrophy but resembles semantic dementia. Whilst the deficits may be attributable wholly to myotonic dystrophy pathology, the co-existence of a form of semantic dementia is also possible. It is noted that the aggregation of tau protein is a neuropathological feature common to both diseases.

Myotonic dystrophy type I in childhood Long-term evolution in patients surviving the neonatal period

In a retrospective study, 32 patients with myotonic dystrophy, including congenital (n=17) and infantile/juvenile forms (n=15) were studied during a long follow-up lasting 7-28 years (median: 17 years). The clinical presentation was extremely variable; however, a continuum did exist between severe and less severe congenital forms, and later-onset forms, without genotype-phenotype correlation. We observed some unusual presentations, such as 3 cases of isolated club-feet during the neonatal period, and 7 patients (23%) with a completely isolated mental deficiency, language delay and school failure, who only completed the clinical picture several years later. Wechsler scale testing was performed in all cases, and repeated with 8 patients. It demonstrated a decrease in intellectual abilities in 5 patients, suggesting the possibility of a degenerative cerebral process occurring in these children. This decrease has also been reported in some adult cases. This study illustrates the extremely heterogeneous clinical presentation of myotonic dystrophy in childhood.

Cognitive profile in childhood myotonic dystrophy type 1: is there a global impairment?

The objective of this study was to assess the cognitive profile in the childhood-onset form of myotonic dystrophy (DM1). We carried out a general cognitive abilities study on 36 patients (6-18 years). Results of Full Scale IQ , VIQ (Verbal IQ) and PIQ (Performance IQ) measures are discussed in terms of global cognitive impairment depending on the (CTG)n repeat size and the transmitting parent's sex. The results highlighted a negative correlation between the CTG repeat size and cognitive function: (1) 55% of the subjects (20/34) presented large CTG expansion (mean=761) correlated with significant extensive cognitive deficits (mean Full Scale IQ=56) in both intelligence scales (verbal and non-verbal); most of them exhibited DM1 maternal transmission. (2) In the case of smaller expansion (mean=527), 38% of the subjects exhibited a subnormal intelligence (mean Full Scale IQ=86) but performed poorly on subtests evaluating attention/memory function and presented a severe deficit in visuospatial and/or visuo-constructive skills. Most of these children had paternal transmission but a few had an affected mother.

Cerebral involvement in myotonic dystrophies

Myotonic dystrophy types 1 (DM1) and 2 (DM2) are similar yet distinct autosomal-dominant disorders characterized by muscle weakness, myotonia, cataracts, and multiple organ involvement, including the brain. One key difference between DM1 and DM2 is that a congenital form has been described for DM1 only. Expression of RNA transcripts containing pathogenic repeat lengths produces defects in alternative splicing of multiple RNAs, sequesters specific repeat-binding proteins, and ultimately leads to developmentally inappropriate splice products for a particular tissue. Whether brain pathology in its entirety in adult DM1 and DM2 is caused by interference in RNA processing remains to be determined. This review focuses on the similarities and differences between DM1 and DM2 with respect to neuropsychological, neuropathological, and neuroimaging data relating to cerebral involvement, with special emphasis on the clinical relevance and social consequences of such involvement.

Cognitive deficits and CTG repeat expansion size in classical myotonic dystrophy type 1 (DM1)

Background

This study was designed to investigate cognitive abilities and their correlations with CTG repeat expansion size in classical Myotonic dystrophy type 1 (DM1), given that earlier studies have indicated cognitive deficits, possibly correlating with blood CTG repeats expansion size.

Methods

A measurement of CTG repeat expansion in lymphocytes and an extensive neuropsychological examination was made in 47 patients (25 women and 22 men). Individual results in the examination were compared with normative data.

Results

A substantial proportion of patients with DM1 (> 40%) scored worse in comparison to normative collectives on tests measuring executive, arithmetic, attention, speed and visuospatial abilities. We found significant correlations between longer CTG repeat expansion size and lower results on most tests associated with these abilities. Furthermore, the association between executive (frontal) deficits and DM1 were strengthened when considering both test results and correlations with CTG repeat expansion size in lymphocytes.

Conclusion

This study showed deficits in several cognitive abilities when patients with DM1 are compared to normative collectives. Some of the neuropsychological tests associated with these abilities are correlated to CTG repeat expansion size in blood. These data highlight the importance of considering cognitive deficits when seeing patients with classical DM1 in clinical practice, but also the utility of using blood CTG repeat expansion size as a broad predictor of finding cognitive deficit in DM1.

Myotonic dystrophy: RNA pathogenesis comes into focus

Myotonic dystrophy (DM)--the most common form of muscular dystrophy in adults, affecting 1/8000 individuals--is a dominantly inherited disorder with a peculiar and rare pattern of multisystemic clinical features affecting skeletal muscle, the heart, the eye, and the endocrine system. Two genetic loci have been associated with the DM phenotype: DM1, on chromosome 19, and DM2, on chromosome 3. In 1992, the mutation responsible for DM1 was identified as a CTG expansion located in the 3' untranslated region of the dystrophia myotonica-protein kinase gene (DMPK). How this untranslated CTG expansion causes myotonic dystrophy type 1(DM1) has been controversial. The recent discovery that myotonic dystrophy type 2 (DM2) is caused by an untranslated CCTG expansion, along with other discoveries on DM1 pathogenesis, indicate that the clinical features common to both diseases are caused by a gain-of-function RNA mechanism in which the CUG and CCUG repeats alter cellular function, including alternative splicing of various genes. We discuss the pathogenic mechanisms that have been proposed for the myotonic dystrophies, the clinical and molecular features of DM1 and DM2, and the characterization of murine and cell-culture models that have been generated to better understand these diseases.

Executive dysfunction and avoidant personality trait in myotonic dystrophy type 1 (DM-1) and in proximal myotonic myopathy (PROMM/DM-2)

A previous study in proximal myotonic myopathy (PROMM/DM-2) and myotonic dystrophy type 1 (DM-1) using brain positron emission tomography demonstrated a reduced cerebral blood flow in the frontal and temporal regions associated with cognitive impairment. The objective was to investigate further cognitive and behavioural aspects in a new series of patients with DM-1 and PROMM/DM-2. Nineteen patients with genetically determined PROMM/DM-2 and 21 patients with moderately severe DM-1 underwent neuropsychological testing and neuropsychiatric interviews. DM-1 and PROMM/DM-2 patients had significantly lower scores on tests of frontal lobe function compared to controls. Neuropsychiatric interviews demonstrated an avoidant trait personality disorder in both patient groups. Brain single photon emission computed tomography showed frontal and parieto-occipital hypoperfusion. The results suggest that there is a specific cognitive and behavioural profile in PROMM/DM-2 and in DM-1, and that this profile is associated with hypoperfusion in frontal and parieto-occipital regions of the brain.