Medicina del trabajo

Inborn errors of metabolism in adults Jean-Marie Saudubray, Frederic Sedel Departement
 des
 maladies
 métaboliques,
 Federation
 des
 maladies
 du
 système
 nerveux,Hopital
Pitié‐Salpêtrière
et
Université
Pierre
et
Marie
Curie
(Paris
VI),
47
boulevard
 de
 l’hopital,75651
 Paris
 cedex
 13,
 France.
 jmsaudubray@orange.fr




 frederic.sedel@psl.aphp.fr Inborn errors of metabolism (IEM) areindividually rare, but collectively numerous. The recent application of tandem mass spectrometry (tandem MS) to newborn screening and prenatal diagnosis has enabled presymptomatic diagnosis for some IEM. However, for most, neonatal screening tests are either too slow, expensive or unreliable and, as a consequence, a simple method of clinical screening is mandatory before initiating sophisticatedbiochemical investigations. The clinical diagnosis of IEM relies upon a limited number of principles: 1.In the appropriate clinical context consider IEM in parallel with other more common conditions. 2. Be aware of symptoms that persist and remain unexplained after the initial treatment and the usual investigations have been performed for more common disorders may be due to an IEM. 3. Do not confuse asymptom or a syndrome with etiology-the underlying cause may be an IEM yet to be defined.4. Remember that an IEM can present at any age, from fetal life to old age.4. Be aware that although most genetic metabolic errors are hereditary and transmitted as recessive disorders, the majority of individual cases appear sporadic .5.Initially consider inborn errors which are amenable to treatment mostlyin the acute emergency situation. 6.Obtain help from specialized centers. Until recently IEMs were considered as a speciality of paediatricians. Indeed the term “inborn” in the mind of clinicians has meant for a long time, a disease which starts in the new born period or at least in childhood. Although paediatricians have learned with time that in addition to severe neonatal forms most IEMs canhave mild forms with first clinical signs starting in adolescence or very late in adulthood, this concept of “adult onset IEMs” has not reached the adult medical community until very recently. Since these late onset forms are often not recognized, their exact prevalence is unknown. Most if not all existing books and diagnostic algorithms refers to paediatric forms of these diseases with the exceptionof several review articles. From a pathophysiological perspective, metabolic disorders can be divided into the following three diagnostically useful groups. Group 1: Disorders which give rise to intoxication. This group includes inborn errors of intermediary metabolism that lead to an acute or progressive intoxication from the

accumulation of toxic compounds proximal to the metabolic block.In this group are the inborn errors of amino acid catabolism (phenylketonuria, maple syrup urine disease, homocystinuria, tyrosinemia etc.), most organic acidurias (methylmalonic, propionic, isovaleric etc.), congenital urea cycle defects, sugar intolerances (galactosemia, hereditary fructose intolerance), metal intoxication (Wilson, Menkes, hemochromatosis), and porphyrias. All the conditions inthis group share clinical similarities: they do not interfere with the embryo-fetal development and they present with a symptom-free interval and clinical signs of “intoxication”, which may be acute (vomiting, coma, liver failure, thromboembolic complications etc.) or chronic (failure to thrive, developmental delay, ectopia lentis, cardiomyopathy etc.). Circumstances that can provoke acutemetabolic attacks include catabolism, fever, intercurrent illness and food intake. Clinical expression is often both late in onset and intermittent. The diagnosis is straightforward and most commonly relies on plasma and urine amino acid, organic acid and acylcarnitine chromatography. Most of these disorders are treatable and require the emergency removal of the toxin by special diets, extra-corporeal...