Résumé :
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Communication n° 525 Myotonic dystrophy type 1 (DM1) is an autosomal-dominant neuromuscular disease with an incidence of 1 in 8000 individuals. The gene is located on the chromosome 19q13.3 and it encodes for a protein with serine-threonine kinase activity (DMPK). The mutation that gives rise to DM1 consists of a CTG repeat expansion in the 3'-untranslated region of the DMPK gene. Four clinical forms have been identified: the late onset form, the classical adult form, the congenital form and, recently, the childhood form. Several studies have analyzed genotype-phenotype correlations with specific regard to cognitive features. Congenital form is characterized by frequent and severe mental retardation whereas in the classical adult form, reasoning, executive functions, long term memory and visuoconstructive abilities are impaired. Evaluation of cognition in the childhood form has been scarcely invastigated. So, we carried out a neuropsychological study on 36 patients aged from 6 to 18 years, with exclusively childhood's phenotype. Data are discussed with Global Intelligence Quotient (IQ), Verbal IQ (VIQ) and non-Verbal IQ (PIQ) measures in terms of global versus selective cognitive impairment depending on the transmitting parent's sex and the (CTG)n repeat size. Results highlight the occurrence of two distinct patterns of cognitive dysfunction: (1) patients with maternal inheritance exhibited an impairment in all measures of global, verbal and non-verbal intelligence which were significantly correlated with the (CTG)n repeat size; (2) patients with paternal inheritance showed subnormal intelligence scores but presented selective impairment of subtests evaluating visuoconstructive abilities and verbal working memory.
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