Middle latency auditory-evoked potentials in myotonic dystrophy: relation to the size of the CTG trinucleotide repeat and intelligent quotient

Myotonic dystrophy types 1 and 2

Myotonic dystrophies (dystrophia myotonica, or DM) are inherited disorders characterized by myotonia and progressive muscle degeneration, which are variably associated with a multisystemic phenotype. To date, two types of myotonic dystrophy, type 1 (DM1) and type 2 (DM2), are known to exist; both are autosomal dominant disorders caused by expansion of an untranslated short tandem repeat DNA sequence (CTG)(n) and (CCTG)(n), respectively. These expanded repeats in DM1 and DM2 show different patterns of repeat-size instability. Phenotypes of DM1 and DM2 are similar but there are some important differences, most conspicuously in the severity of the disease (including the presence or absence of the congenital form), muscles primarily affected (distal versus proximal), involved muscle fiber types (type 1 versus type 2 fibers), and some associated multisystemic phenotypes. The pathogenic mechanism of DM1 and DM2 is thought to be mediated by the mutant RNA transcripts containing expanded CUG and CCUG repeats. Strong evidence supports the hypothesis that sequestration of muscle-blind like (MBNL) proteins by these expanded repeats leads to misregulated splicing of many gene transcripts in corroboration with the raised level of CUG-binding protein 1. However, additional mechanisms, such as changes in the chromatin structure involving CTCN-binding site and gene expression dysregulations, are emerging. Although treatment of DM1 and DM2 is currently limited to supportive therapies, new therapeutic approaches based on pathogenic mechanisms may become feasible in the near future.

Correlation among subcortical white matter lesions, intelligence and CTG repeat expansion in classic myotonic dystrophy type 1

OBJECTIVES

To analyze the correlation among intelligence, brain magnetic resonance images (MRI) and genotype in classic myotonic dystrophy type 1 (DM1) patients.

MATERIALS AND METHODS

Seventeen patients with classic DM1 were administered intelligence and neuropsychological tests and brain MRI focusing on a semi-quantitative rating scale of subcortical white matter lesions (WMLs). Statistical analysis was measured to evaluate the correlation among clinical manifestations, intelligence, brain MRI abnormalities, and CTG repeat expansion.

RESULTS

There were statistically significant correlations between intelligence test and insular WMLs for all DM1 patients and between intelligence quotient and temporal WMLs for those patients with less than 400 of the CTG repeat size. We also documented that temporal WMLs were related to the disease course, and frontal WMLs were correlated with aging in all DM1 patients. However, a poor correlation was found among CTG repeat size and clinical pictures, neuropsychological impairments, and brain MRI abnormalities in all DM1 patients.

CONCLUSION

These results suggest that subcortical WMLs are correlated with focal dementia in classic DM1 patients. Temporal and insular WMLs may be responsible for the global intellectual dysfunction of adult DM1 patients.

Objective response detection technique in frequency-domain for reflecting changes in MLAEP

The mid-latency auditory evoked potential (MLAEP) occurs within the interval 10-100ms post-stimulus and exhibits morphological changes due to coma, general anaesthesia and neurological and psychiatric diseases. This work evaluates an objective response detection technique in the frequency domain, the magnitude squared coherence (kappa(2)(f)), in reflecting MLAEPs changes in amplitude and latencies. Both simulation and EEG data were used in this investigation. The EEG during auditory stimulation in 10 volunteers under propofol-induced anaesthesia was acquired. Based on the null hypothesis of non-existing response, critical values have been derived in order to detect the auditory response. The alternative hypothesis was used to infer about maximal-response frequencies as well as to derive confidence intervals for the estimated values of kappa(2)(f) during anaesthesia. Changes in both simulated and real MLAEPs could be tracked by kappa(2)(f), even for low SNR. High degree of cortical activation occurred predominantly between 30 and 90Hz. This finding could be related to the sensory-originated phase-locked oscillation in the gamma band (30-70Hz). Hence, for applications where changes on MLAEPs should be assessed, the use of kappa(2)(f) as an objective statistical response detection technique is worth to be applied.