Language and cognition in children with metachromatic leukodystrophy: onset and natural course in a nationwide cohort

BACKGROUND Metachromatic leukodystrophy (MLD) is a rare, genetic neurodegenerative disease. It leads to progressive demyelination resulting in regression of development and early death. With regard to experimental therapies, knowledge of the natural course of the disease is highly important. We aimed to analyse onset and character of first symptoms in MLD and to provide detailed natural course data concerning language and cognition. METHODS Patients with MLD were recruited nationwide within the scope of the German research network LEUKONET. 59 patients' questionnaires (23 late-infantile, 36 juvenile) were analysed. RESULTS Time from first symptoms (at a median age of 1.5 years in late-infantile and 6 years in juvenile MLD) to diagnosis took one year in late-infantile and two years in juvenile patients on average. Gait disturbances and abnormal movement patterns were first signs in all patients with late-infantile and in most with juvenile MLD. Onset in the latter was additionally characterized by problems in concentration, behaviour and fine motor function (p=0.0011, p<0.0001, and p=0.0012). Half of late-infantile patients did not learn to speak in complete sentences after an initially normal language acquisition. They showed a rapid language decline with first language difficulties at a median age of 2.5 years and complete loss of expressive language within several months (median age 32, range 22-47 months). This was followed by total loss of communication at a median age of around four years. In juvenile patients, language decline was more protracted, and problems in concentration and behaviour were followed by decline in skills for reading, writing and calculating around four years after disease onset. CONCLUSIONS Our data reflect the natural course of decline in language and cognition in late-infantile and juvenile MLD in a large cohort over a long observation period. This is especially relevant to juvenile patients where the disease course is protracted and prospective studies are hardly feasible. Knowledge of first symptoms may lead to earlier diagnosis and subsequently to a better outcome following therapeutic intervention. Our data may serve as a reference for individual treatment decisions and for evaluation of clinical outcome after treatment intervention.