Nouveautés radiologiques dans le dépistage et le diagnostic des erreurs innées du métabolisme

Les maladies héréditaires du métabolisme ont acquis une place de plus en plus importante dans la pathologie pédiatrique. Leur nombre ne cesse d’augmenter au fur et à mesure de la progression des connaissances en biologie cellulaire et des progrès techniques d’investigation. Nous traiterons ici de trois maladies métaboliques que l’imagerie fonctionnelle et la spectroscopie IRM ont permis d’identifier. Il s’agit des déficits en créatine traitables par l’administration de créatine et les défauts du métabolisme des polyols qui ouvrent le champ sur de nouveaux déficits enzymatiques responsables de présentations cliniques très variées. Nous aborderons également les hyperinsulinismes du jeune enfant dont le diagnostic et la prise en charge ont été récemment transformées par l’utilisation de la [18F]-fluoro-L-DOPA en tomographie par émission de positons.New metabolic diseases are regularly identified by a genetic or biochemical approach. Indeed, the metabolic diseases result from an enzymatic block with accumulation of a metabolite upstream to the block and deficit of a metabolite downstream. The characterization of these abnormal metabolites by MRI spectroscopy permitted to identify the deficient enzyme in two new groups of diseases, creatine deficiencies and polyol anomalies. Creatine deficiency is implicated in unspecific mental retardation. A low peak of creatine at MRI spectroscopy is evocating of creatine deficiency which is treatable by creatine administration. Deficiency of synthesis of polyols, metabolites on the pentose pathway, represent new described metabolic diseases with variable symptoms including a neurological distress, liver disease, splenomegaly, cutis laxa and renal insufficiency. The deficit of ribose-5-phosphate isomerase, one of the enzymes whose diagnosis is evoked in front of the accumulation of ribitol, arabitol and xylitol leads to a leucodystrophy in adults. This new deficit was highlighted by the identification of an abnormal peak in cerebral MRI-spectroscopy corresponding to the abnormal accumulation of polyols in brain. Congenital hyperinsulinism (HI) is characterized by profound hypoglycaemia related to inappropriate insulin secretion. Focal and diffuse forms of hyperinsulinism share a similar clinical presentation but their treatment is dramatically different. Until recently, preoperative differential diagnosis was based on pancreatic venous sampling, an invasive and technically demanding technique. Positron emission tomography (PET) after injection of [18F]Fluoro-L-DOPA has been evaluated for the preoperative differentiation between focal and diffuse HI, by imaging uptake of radiotracer and the conversion of [18F]Fluoro-L-DOPA into dopamine by DOPA decarboxylase. PET with [18F]Fluoro-L-DOPA has been validated as a reliable test to differentiate diffuse and focal HI and is now a major differential diagnosis tool in infantile hyperinsulinemic hypoglycaemia

Long-term neurological outcome of a cohort of 80 patients with classical organic acidurias.

International audienceBACKGROUND: Classical organic acidurias including methylmalonic aciduria (MMA), propionic aciduria (PA) and isovaleric aciduria (IVA) are severe inborn errors of the catabolism of branched-chain amino acids and odd-numbered chain fatty acids, presenting with severe complications. METHODS: This study investigated the long-term outcome of 80 patients with classical organic aciduria (38 with MMA, 24 with PA and 18 with IVA) by integrating clinical, radiological, biochemical and genetic data. RESULTS: Patients were followed-up for a mean of 14 years [age 3.3-46.3 years]. PA included a greater number of patients with abnormal neurological examination (37% in PA, 24% in MMA and 0% in IVA), lower psychometric scores (abnormal evaluation at age 3 years in 61% of patients with PA versus 26% in MMA and 18% in IVA) and more frequent basal ganglia lesions (56% of patients versus 36% in MMA and 17% in IVA). All patients with IVA presented a normal neurological examination and only 1/3 presented cognitive troubles. Prognosis for MMA was intermediate. Biochemical metabolite analysis excluding acute decompensations revealed significant progressive increases of glycine, alanine and glutamine particularly in PA and possibly in MMA but no correlation with neurological outcome. A significant increase of plasma methylmalonic acid was found in MMA patients with intellectual deficiency (mean level of 199 mumol/L versus 70 mumol/L, p < 0.05), with an estimated significant probability of severe outcome for average levels between birth and age 6 years above 167 mumol/L. Urinary 3-hydroxypropionate (3-HP) levels were significantly higher in PA patients with intellectual deficiency (mean level of 68.9 mumol/mmol of creatinine versus 34.6 mumol/mmol of creatinine, p < 0.01), with an estimated significant probability of severe outcome for average levels between birth and age 6 years above 55 mumol/mmol. As for molecular analysis, prognosis of MMA patients with mutations involving the MMAA gene was better compared to patients with mutations involving the MUT gene. CONCLUSION: Propionic aciduria had the most severe neurological prognosis. Our radiological and biochemical data are consistent with a mitochondrial toxicity mechanism. Follow-up plasma MMA and urinary 3-HP levels may have prognostic significance calling for greater efforts to optimize long-term management in these patients

Neonatal hypoglycaemia: aetiologies

International audienceDiagnosis of glucose status requires knowledge of the homeostatic mechanisms that maintain the blood glucose concentration between the narrow range of 2.5 and 7.5 mmol/l during periods of eating or fasting. Hypoglycaemia occurring within the first few hours after eating is suggestive of hyperinsulinism. Most glucose is subsequently converted into glycogen in the liver, and hypoglycaemia occurring during this phase is suggestive of glycogenosis. During fasting, gluconeogenesis progressively replaces glycogen as the major source of blood glucose, and hypoglycaemia occurring during this period is suggestive of impaired gluconeogenesis or fatty acid disorders. Growth hormone, glucagon, cortisol and insulin-like growth factor 1 deficiencies may also play a role. Other causes of hypoglycaemia have also been identified recently, namely glucose transporter disorders, respiratory chain disorders and congenital disorders of glycosylation

Les nouvelles maladies héréditaires du métabolisme du programme français de dépistage néonatal

Les maladies héréditaires du métabolisme (MHM) sont un groupe de maladies rares et cliniquement hétérogènes. Le retard diagnostique est fréquent, conduisant souvent au décès du patient ou à de graves séquelles. Certaines MHM entraînent l’accumulation de métabolites intermédiaires circulant dans le sang, qui sont détectables par une méthode commune utilisant la spectrométrie de masse en tandem. Cette méthode permet la reconnaissance simultanée de plusieurs de ces maladies affectant différentes voies métaboliques. En France, le programme de dépistage néonatal (DNN) des MHM, longtemps limité à la phénylcétonurie, a récemment été étendu au déficit en déshydrogénase des acyl-CoA à chaîne moyenne (MCADD). Le rationnel, la méthode et l’organisation de ce nouveau DNN sont décrits dans cet article. Sept nouvelles MHM (leucinose, homocystinurie, tyrosinémie de type I, acidurie glutarique de type I, acidurie isovalérique, déficit en déshydrogénase des hydroxy-acyl-CoA à chaîne longue, déficit du transporteur de la carnitine) devraient être dépistées, grâce à une prochaine extension du programme de DNN. Des efforts sont nécessaires pour mieux comprendre et prévoir la signification de chaque test anormal à la naissance, diminuer les taux de faux positifs, et développer les stratégies de prise en charge adéquates

First Report of a Patient with MPS Type VII, Due to Novel Mutations in GUSB, Who Underwent Enzyme Replacement and Then Hematopoietic Stem Cell Transplantation

We report the case of a boy who was diagnosed with mucopolysaccharidosis (MPS) VII at two weeks of age. He harbored three missense &beta;-glucuronidase (GUSB) variations in exon 3: two novel, c.422A&gt;C and c.424C&gt;T, inherited from his mother, and the rather common c.526C&gt;T, inherited from his father. Expression of these variations in transfected HEK293T cells demonstrated that the double mutation c.422A&gt;C;424C&gt;T reduces &beta;-glucuronidase enzyme activity. Enzyme replacement therapy (ERT), using UX003 (vestronidase alfa), was started at four months of age, followed by a hematopoietic stem cell allograft transplantation (HSCT) at 13 months of age. ERT was well tolerated and attenuated visceromegaly and skin infiltration. After a severe skin and gut graft-versus-host disease, ERT was stopped six months after HSCT. The last follow-up examination (at the age of four years) revealed a normal psychomotor development, stabilized growth curve, no hepatosplenomegaly, and no other organ involvement. Intriguingly, enzyme activity had normalized in leukocytes but remained low in plasma. This case report illustrates: (i) The need for an early diagnosis of MPS, and (ii) the possible benefit of a very early enzymatic and/or cellular therapy in this rare form of lysosomal storage disease

Factitious hyperinsulinism leading to pancreatectomy: severe forms of Munchausen syndrome by proxy.

Clinical history and inappropriate insulin secretion during hypoglycemic episodes permit the diagnosis of hyperinsulinism. We report 2 cases of factitious hyperinsulinism leading to partial pancreatectomy. Case 1 was an 8-year-old girl who presented with severe hypoglycemia and elevated insulin and C-peptide levels. Catheterization of pancreatic veins was performed to localize the excess insulin secretion. Insulinoma was suspected, and partial pancreatectomy was performed. Ten days after surgery, severe hypoglycemia recurred with severely elevated plasma insulin levels (x100) but very low C-peptide plasma levels, suggesting factitious hyperinsulinemia. Hypoglycemic episodes before surgery were provoked by oral sulfonamides; postoperative episodes were caused by parenteral insulin. Falsified prescriptions for sulfonamides and insulin by the mother, a nurse, were found. Case 2 was a 6-month-old girl who presented with seizures and hypoglycemia but had a symptom-free interval of many months afterward. At 2 years of age, repeated hypoglycemic seizures and elevated insulin plasma levels suggested congenital hyperinsulinism. C-peptide plasma level, measured once, was normal, but blood sampling was performed 15 minutes after a hypoglycemic episode. Partial pancreatectomy was performed. Two weeks after surgery, hypoglycemic seizures recurred, and the patient was admitted for pancreatic vein catheterization. This investigation was performed during hypoglycemia and revealed high insulin levels and undetectable C-peptide levels, suggesting factitious hypoglycemia. Insulin/C-peptide ratio analysis is crucial to assess factitious hypoglycemia, although sulfonamide-induced hypoglycemia is not thereby detected. One percent (2 of 250) of all cases of hyperinsulinemic hypoglycemia in our unit have been identified as Munchausen syndrome by proxy. Atypical disease history should raise the question of factitious hypoglycemia

Respiratory Chain Defects May Present Only with Hypoglycemia

International audienceHypoglycemia occasionally results from oxidative phosphorylation deficiency, associated with liver failure. Conversely, in some cases of respiratory chain defect, the impairment in glucose metabolism occurs with normal hepatic function. The mechanism for this hypoglycemia remains poorly understood. We report here three unrelated children with hypoglycemia as the presenting symptom associated with oxidative phosphorylation deficiency but without liver dysfunction. Two patients had, respectively, complex III and complex IV deficiency and presented with long fast hypoglycemia. During a fasting test, the first patient showed evidence for impaired gluconeogenesis (progressive increase of plasma lactate and no decrease of alanine levels), whereas the second patient appeared to have impaired fatty acid oxidation (hypoketotic hypoglycemia with increased levels of non esterified fatty acids). The third patient presented with both long and short fast hypoglycemia related to complex IV deficiency. The mechanism of hypoglycemia for this patient may have been partly related to GH insufficiency, whereas impaired glycogen metabolism possibly accounted for short fast hypoglycemia. We suggest that hypoglycemia can be the presenting symptom for respiratory chain defects, through the possible reduction in cofactors resulting from oxidative phosphorylation deficiency, and that respiratory chain defects should therefore be considered in the differential diagnosis of hypoglycemia

Massive subdural haematomas in Menkes disease mimicking shaken baby syndrome.

INTRODUCTION: Menkes disease is an X-linked inherited disorder of intestinal copper absorption resulting in copper deficiency. Cardinal features include hair abnormalities, facial dysmorphism, severe neurological impairment, hypothermia, arterial anomalies, bone abnormalities and a fatal outcome. CASE REPORT: We present a case of Menkes disease complicated by progressive macrocephaly following the development of massive subdural haematomas. These lesions associated with femoral metaphyseal spurs could be confused with nonaccidental injury such as that seen in the shaken baby syndrome. DISCUSSION: This case emphasises that Menkes disease, like glutaric aciduria type 1, should be included in the differential diagnosis of unexplained subdural haematomas and neurological deficits in infants