Forme infantile de la dystrophie myotonique de type 1 (DM1) et troubles du spectre autistique (TSA): Existe-t-il une comorbidité?

Myotonic dystrophy type 1 (DM1) is an autosomal multisystemic dominant disease caused by the expansion of a CTG triplet repeat within the 3' untranslated region of dystrophy myotonic protein kinase (DMPK) gene on chromosome 19q13.3. The occurrence of a brain involvement is now widely accepted and well-recognized as a common feature in a substantial proportion of DM1 population. Depending of the phenotypic expression, the degree of cognitive impairment remains heterogeneous, ranging from moderate to severe mental retardation, which is characteristic of the congenital form, to executive, visuospatial and personality dysfunction in the adult-onset form. In contrast, studies exploring the cognitive or psychiatric impairments in the childhood DM1 are scarce and show conflicting results in regards to a comorbid diagnosis of Autism Spectrum Disorders (ASD). The objective of this article is to examine, on the basis of previous clinical studies, the plausible co-occurrence of childhood DM1 and ASD by (1) highlighting the specific cognitive and psychiatric profiles reported in both populations and (2) comparing the neuroanatomical and neuro-functional features of these two pathologies. For cognitive ability, the mean full-scale IQ of individuals with the childhood form of DM1 was globally assessed in the borderline range but a significant discrepancy was found with performance IQ being lower than verbal IQ. In ASD subjects with no mental retardation, a reverse dissociation was predominantly reported with lower VIQ than PIQ. Concerning psychiatric disorders in childhood DM1, most of the studies found that internalizing disorders were the most frequent whereas one study reported high prevalence of ASD. However, the DM1 patients with ASD were described as correlating with severity of DM1 and intellectual disability. Executive functions (predominantly working memory deficit in childhood DM1) and alexithymia or social cognition impairments were observed in both pathologies. Brain imaging studies in the childhood phenotype of DM1 revealed white matter abnormalities with no evidence of regional variation while a disrupted cortical connectivity pattern was suggested in ASD population. In conclusion, it could be hypothesized that different forms of DM1 illustrate a continuum of dysfunctions in the area of socialization (isolation, lack of initiative in social interactions, social anxiety and autism) as suggested by Douniol et al. (2012). Recognition of specific cognitive and psychiatric features in the childhood-onset form of DM1 should be fundamental for detecting early symptoms and implementing optimal individual support.