Cognitive Decline Seen in Myotonic Dystrophy Type 1 Children: Study

Declines included frequent impairments in visuospatial skills and attention

Steve Bryson, PhD avatar

by Steve Bryson, PhD |

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Children with myotonic dystrophy type 1 (DM1) showed a decline in cognitive function over two years, with frequent impairment in visuospatial skills and attention, a small study suggested.

The data indicate cognitive, neuropsychological, emotional, and behavioral assessments should be administered to children with DM1 periodically during development, the researchers said.

They noted that larger studies are needed to better evaluate the neurological changes over time and inform practice.

The study, “Cognitive, neuropsychological and emotional-behavioural functioning in a sample of children with myotonic dystrophy type 1,” was published in the European Journal of Paediatric Neurology.

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DM1 is marked primarily by progressive muscle weakness and prolonged muscle contractions (myotonia) that are unable to relax after use. DM1 can also cause heart problems, hormone and digestive tract difficulties, excessive fatigue, and cognitive and psychological impairment.

Although it’s mainly seen in adults, it can also occur in children and newborns. Congenital DM1 presents with severe low muscle tone and weakness at birth, breathing and nutritional problems, intellectual disability, and a high mortality rate. In childhood DM1, mild motor delay with low muscle tone is common, with early signs of learning difficulties and behavioral and mood complications.

Few studies following children with DM1 have been conducted so far, however.

Researchers at the University of Turin, Italy, sought to apply a series of neuropsychological tests to congenital and childhood DM1 patients and identify changes that occurred over two years.

The team recruited five patients with congenital DM1 and five with childhood DM1 between 18 months and 16 years. Symptom onset occurred at birth for all those with congenital DM1 and between ages 6–9 for childhood DM1 patients. There was no decline in motor function across all participants during the two-year study period.

Initial intelligence quotient (IQ) assessments found a mean IQ of 72, ranging from 38 to 106. Intellectual disability was detected in four with congenital DM1, from mild to moderate, and one with childhood DM1, considered mild.

After two years, intellectual disability was confirmed in all three evaluated congenital patients, ranging from mild to severe, and two out of three childhood patients, from mild to moderate. All the children showed a decline in cognitive performance compared to the initial evaluation — the mean IQ dropped from 72 to 53 after two years.

“These results highlight the importance of IQ evaluation in DM1 paediatric population,” the researchers wrote.

A visuospatial function test (TPV), related to the visual perception of the spatial relationships of objects, showed all three congenital DM1 children who were evaluated were under the 10th percentile, considered abnormal, in the four domains — eye-hand coordination, position in space, copying and reproduction, and figure-ground.

Childhood DM1 participants showed results under the 10th percentile in some domains. After two years, the visuospatial test was performed on one eligible childhood case who was in the normal range except for copying and reproduction. As a result, “no informative data on progression could be obtained from our study,” the researchers noted.

In the Bells assessment for attention, all congenital DM1 children showed abnormal results for rapidity and accuracy domains tests. Among childhood cases, all performed well in the rapidity domain and two had abnormal results with accuracy.

At two years, one eligible congenital case showed normal rapidity and abnormal accuracy, while all with childhood DM1 scored in the normal range. “No clear trend was observed at the follow-up evaluation,” the researchers added.

Executive functions were evaluated with the Tower of London test, a measure of planning ability, in seven participants. Initially, all had normal scores. In the four eligible patients at two years, one congenital DM1 patient scored below the normal range, two childhood DM1 patients had normal results, and one was below standard.

Emotional-behavioral problems were determined with the Child Behaviour Checklist (CBCL), a questionnaire for parents or guardians. Among the seven completed questionnaires at the study’s start, the total competence score related to activities, social, and school, was in the clinical range in six (86%) patients, particularly on the activities scale. Similar results were seen after two years in the four cases with data.

“Even in the limited case series of the present study, the pattern of a neurodevelopmental disorder seems to emerge,” the researchers concluded. “These data suggest that a comprehensive protocol should include cognitive, neuropsychological, emotional, and behavioural assessment, and should probably be administered periodically to DM1 paediatric patients during their development.”

“Larger longitudinal studies are needed to better evaluate the trajectories over time and inform practice,” they added.