Reading difficulties in duchenne muscle dystrophy patients : basis of verbal working memory in cerebellar circuits

Abstract

Duchenne Muscle Dystrophy (DMD) is an X-linked genetically inherited disorder, leading to profound muscle weakness and specific cognitive deficits hampering reading capacity and general academic functioning. Improving fundaments for assessing the DMD children in more specific ways will be crucial for understanding and addressing their special needs for educational support and psychological scaffolding. This work will compare the DMD readers to groups with developmental dyslexia and cerebellar lesion patients showing a wide range of working memory, and language deficits affecting their reading process. The DMD group has been described with specific verbal working memory deficits, specifically pointing towards the inability to perceive sequences of information, a core basis for fluent reading. In addition, difficulties on procedural, attentional and phonological level adds to the risk of dyslexia in DMD. Working memory deficits in DMD can be regarded as a consequence of cerebellar dysfunction. Verbal working memory and sequencing deficits are also found in patients with cerebellar lesions and actualized in reading by the cerebellar hypothesis of dyslexia. A link between DMD dystrophin deficiency, expressed in cerebral and cerebellar tissues, and cognitive impairment in the DMD group is suggested. Placing the cerebellum as a central part in a cerebro-cerebellar signal pathway, and reviewing findings of cerebellar dysfunction in the DMD group, working memory processes and phonological processing, and sequenced memory processes specifically, are plausibly connected to cerebellar function. Using the working memory model presented by Baddeley (2011), the working memory concepts are combined and discussed within current findings from neural imaging and lesion studies, animal models, genetic mapping studies, tissue analyses and neuropsychological assessment methods. The understanding of reading problems in DMD will be drawn from molecular genetics to assessment of practical reading skills, discussing whether these problems could be a result of cerebellar dystrophin deficiency.