Characterization of the pattern of cognitive impairment in myotonic dystrophy type 1.

BACKGROUND Central nervous system involvement occurs in most patients with myotonic dystrophy type 1 (DM1): mental retardation characterizes congenital forms, while a mild cognitive impairment has been described in adult patients with classic DM1. Neuropathological studies documented neurofibrillary tangles and an aberrant tau-protein expression in brain tissues of patients and animal models of DM1. OBJECTIVES To characterize the pattern of cognitive dysfunction occurring in DM1 and to analyze genotype-phenotype correlations in patients with DM1. METHODS We assessed the results of a detailed neuropsychological study, including Mini-Mental State Examination, memory, linguistic level, praxis, attentional and frontal-executive tasks, in a group of 70 patients with DM1, including 10 congenital and 60 classic forms. Statistical analysis of data was performed using analysis of variance for multiple tests. RESULTS Our study documented 2 distinct patterns of cognitive impairment in DM1: in particular, we confirmed the presence of a cognitive pattern characteristic of mental retardation in congenital cases, whereas in adult forms we documented an aging-related decline of frontal and temporal cognitive functions. No correlations were found between cognitive impairment and (CTG)(n) in leukocytes or severity of muscle involvement. CONCLUSIONS Adult patients with DM1 frequently develop, with aging, a focal dementia: such findings agree with recent studies documenting an abnormal tau-protein expression in the brain tissues of patients with DM1. Cognitive decline may represent the only relevant clinical manifestation of DM1 in patients carrying very small (CTG)(n) expansions in leukocytes.