[Adult-onset metabolic diseases]

Inborn errors of metabolism (IEM) can have their onset in adolescence or in adulthood. Although it is difficult to contribute exact data on prevalence -because there are few studies in this respect, and IEM are regarded as infrequent- their detection is important due to the possibilities for therapy and family genetic counselling. The main symptoms of IEM in the adult are neurological, followed by hepatic. Two basic modes of onset can be established. One is acute, normally taking the form of consciousness alteration, lethargy, coma of unknown etiology in a previously healthy patient (urea cycle deficits, homocysteine remethylation disorders and porphyries are the most frequent causes). The other is an insidious, often progressive, chronic symptomathology that can involve complex clinical features, and more rarely a symptom that is isolated in a persistent way (Wilson's disease, mitochondrial diseases, lysosomal storage disorders, Refsum's disease and glycogenosis are some examples of this group). It is especially important to determine the forms of acute onset as these can present situations of extreme emergency where appropriate conduct can prevent the death of the patient. In this case, simple laboratory examinations, such as determination of ammonia, homocysteine, lactate, acylcarnitines, amino acids, organic and porfirines, can guide the diagnosis and enable the start of intensive treatment. This article provides a practical approach that deals with the general characteristics and the clinical keys for suspecting the most usual IEMs in the adult.