[Orientation of mental retardation from neurometabolic diseases]

Isolated mental retardation is rarely caused by metabolic factors. The application of a standardised protocol offers low diagnostic performance. There is no international agreement about what type of metabolic examination must be applied in patients with unspecific mental retardation. Nevertheless, and although they are infrequent, there are a number of inborn errors of metabolism that can present in this way. Urea cycle disorders, different forms of homocystinuria, creatine transport deficiency, 4-hydroxybutyric aciduria, Sanfilippo disease, adenylosuccinate lyase deficit and certain extraordinarily rare congenital disorders of the glycosylation of proteins are some examples of them. It is important first to consider those for which treatment is available and that could be diagnosed genetically for possible family counselling.

Rather than applying a standardised study protocol it is essential is to perform a thorough appraisal of the signs and symptoms associated with the mental retardation (psychiatric disorders, autistic traits, predominant compromise of language, signs of cerebellar dysfunction, epilepsy, dysmorphic traits), since in most disorders it is necessary to apply specific analyses, which are not included in conventional metabolic studies and are only available in certain reference centres.