Iranian Journal of Child Neurology (IJCN)
Volume:6 Issue: 1, Winter 2012

Organic acidemias, also known as organic acidurias, are a group of disorders characterized by increased excretion of organic acids in urine. They result primarily from deficiencies of specific enzymes in the breakdown pathways of amino acids or from enzyme deficiencies in beta oxidation of fatty acids or carbohydrate metabolism. Organic acids also are found in the urine of some patients with mitochondrial disease.Most organic acidemias become clinically apparent during the newborn period or early infancy. After an initial period of well-being, affected children develop a life-threatening episode of metabolic acidosis characterized by an increased anion gap. This presenting episode may be mistaken for sepsis, and if unrecognized, is associated with significant mortality.Children with an organic acidemia are susceptible to metabolic decompensation during episodes of increased catabolism, such as intercurrent illness, trauma, or surgery. Parents and clinicians must be well informed about the initial signs of decompensation and trained in applying an emergency regimen. Surgeons and anesthesiologists should be aware of potential complications and their prevention during anesthesia and surgery.Diagnosis has been facilitated through the use of gas chromatograph-mass spectrometry (GC-MS) and tandem mass spectrometry. Prenatal diagnosis is available for most disorders by detection of diagnostic compounds in amniotic fluid; by analysis of enzyme activities in amniocytes or chorionic villi; by molecular analysis; or by a combination of the three. Diagnosis also may be made through newborn screening by tandem mass spectrometry. Laboratory findings are an essential part of the diagnostic approach to organic acidemias. In most organic acidemias, metabolism of glucose, ketone bodies, and ammonia is deranged primarily or secondarily, in addition to derangement of the acid-base balance. Hypoglycemia, lactic and/or ketoacidosis, and hyperammonemia of varying severity accompany the overt or compensated acidosis. In most instances, a definite diagnosis will be achieved by gas chromatography/mass spectrometry (GC/MS) studies of the urine.However sometimes definite diagnosis by clinical and laboratory assessments is not conclusive, in this cae diagnostic approach must be supported by loading tests. The majority of organic acidemias may be treated by limiting the source of intake or removing the toxic intermediary metabolite. In the case of disorders lacking an effective treatment, an early diagnosis could lead to proper genetic counseling of the parents and to the option of reliable prenatal diagnosis of future pregnancies.

A clinical presentation of a metabolic disorder, often first seen in infants who present with poor feeding, vomiting, tachypnea, acidosis, hyperammonemia, ketosis, ketonuria, irritability, and convulsions or hypotonia and lethargy, findings that are otherwise suggestive of neonatal sepsis Diseases with OA Isovaleric and propionic acidemias, maple syrup urine disease, medium chain acyl dehydrogenase deficiency, glutaric, methylmalonic, formiminoglutamic acidurias.DescriptionThe term “organic acidemia” or “organic aciduria” (OA) applies to a diverse group of metabolic disorders characterized by the excretion of non-amino organic acids in urine. Most organic acidemias results from a dysfunction of a specific step in amino acid catabolism, usually due to deficient enzyme activity. This leads to the accumulation of organic acids in the biological fluids (blood and urine), which, in turn, produces disturbances in the acid-base balance and causes alterations in pathways of intermediary metabolism.Methylmalonic acidemia occurs when the activity of Methylmalonyl CoA mutase is defective in the isoleucine, valine, methionine and threonine degradative pathway.Propionic acidemia occurs when the activity of Propionyl CoA carboxylase isdefective in the isoleucine, valine, methionine and threonine degradative pathway.Isovaleric acidemia occurs when the activity of Isovaleryl CoA dehydrogenase is defective in the leucine degradative pathway.Glutaric acidemia type I occurs when the activity of Glutaryl CoA dehydrogenase is defective in the lysine, hydroxylysine and tryptophan degradative pathway.3-Hydroxy-3-methylglutaryl CoA (HMG-CoA) lyase deficiency occurs when the activity of HMG CoA lyase is defective in the leucine degradative pathway.3-Methylcrotonyl CoA carboxylase deficiency occurs when the activity of 3-methylcrotonyl-CoA carboxylase is defective in the leucine degradative pathway.IncidenceWhile each individual disorder is rare, overall incidence of organic acidemias is 1:20, 000

Inborn errors of organic acid metabolism are relatively recently recognized diseases with a wide spectrum of clinical signs and symptoms: ranging from asymptomatic, normal appearing children to death during first few days of life.In my presentation I will try to explain some of the most common clinical presentation of these disorder with stress on neurologic findings. Organic acidemia usually have three clinical manifestations Severe neonatal form, Intermittent late-onset form and chronic progressive form. Recurrent coma, The main feature of these disorders is due to accumulation of toxic metabolites in Central Nervous system with direct effect on the function, while chronic accumulation of these materials may interfere with CNS development or cerebral metabolism leading to developmental delay.Severe neonatal formsFollowing a symptom free interval of a few days from birth, poor sucking and difficult feeding appears in the newborn, followed by unexplained and progressive coma. Seizures may appear during the course of the disease and EEG may show a burst-suppression pattern. During this stage most infants have axial hypotonia with peripheral dystonia, choreoathetosis, episodic opisthotonus and some repetitive bicycling and boxing movements.Associated biochemical abnormalities including metabolic acidosis, ketonuria and hyperammonemia also is usually present. The overall short-term prognosis with recent advances in medical care is improving. But later in life acute intercurrent episodes triggered by a stress often occur, which can be occasionally fatal.bulging fontanelle and cerebral edema may mimic CNS infection in these babies.Intermittent late-onset formsRecurrent attacks of coma or lethargy with ataxia can occur in childhood or even in adolescence or adulthood. These episodes may be frequent, though in between these the child is entirely normal. These attacks are precipitated by conditions that enhance protein catabolism (trauma, infection etc).Sometimes these episodes can lead to death or severe sequel. Seizure disorder is one of these sequels which is generalized in type with myoclonic seizure in infancy and childhood and later tonic-clonic and atypical absence seizures predominate.

This condition is due to deficiency in electron transport flavoprotein or electron transport fluvoprotein dehydrogenase.The clinical presentation is characteristic of fatty acid oxidation disorders. This disorder is poor prognostic and death in infancy is common.The central nervous system involving causes neurodevelopmental delay, hypotonia, and head lag. Different type of seizures such as infantile spasm and generalized tonic clonic seizure begin in infancy and become refractory to antiepileptic drugs. Also episodes of status epilepticus are frequent. Neurological exam shows manifestation of upper motor neuron disease including exaggerated deep tendon reflex, ankle clonus and positive Babinski sign.Infectious disease and Intercurrent illnesses may lead to neurological deterioration and coma or death in the first few years of life. Also hemorrhagic episodes, for example, petechiae, ecchymose, hematuria and blood in stool associated with infectious disease is common manifestation.The hematologic investigations show no evidence of abnormalities in clotting and platelet function.The facial features of these patients resemble to each other and are mildly dismorphic. Sometimes the nasal bridge is depressed.Neuroimaging evaluation revealed delayed myelination and frontotemporal atrophy with high T2 intensity in basal ganglia.Acute catabolic state with crises of lactic academia and hypoglycemia are frequent but lactate and pyruvate can remain high between attacks.During attacks lactate level as high as 17 mmol/l and acidosis is more severe with PH values of 7.05 to 7.10.The major metabolic abnormality is high excretion of ethylmalonic acid in the urine.This disorder is transmitted in an autosomal recessive trait and boys and girls have been reported in same family.Ethyl malonicaciduria is lethal during infancy or first few years of life. Treatment with carnitine, vitamin C, vitamin D and riboflavin did not show dramatic effect. Diet with restricted methionine is helpful for decrease excretion of ethylmalonic acid in the urine and decrease the level of serum lactate and pyruvate.

Organic acid occur as physiologic intermediates in variety of intracellular metabolic pathways, such as catabolism of aminoacid, mitochondrial β oxidation of fatty acids, tricarboxilic acid cycle, and cholestrol and fatty acid biosynthesis. The classical organic aciduria represent the pursuit of abnormalities of aminoacid degradation beyond deamination Their diagnostic hallmark is an accumulation of characteristic organic acids.The clinical features result from toxicity of the accumulating methabolites.Treatment involved 1. protein restriction 2. supplementation of aminoacids with unimpaired metabolism as well as trace elements and 3. specific measures for detoxification if indicated. Diagnostic tests consist of CBC, FBS, Bun, Cr, uric organic acid, TG, Cholestrol Ca, P, ALP, VBG, Na, K, Cl, U/A(PH, SG, Ketone), Ammonia, lactate, pyrovate, Ketone body CPK, Aldolase, SGOT, SGPT, BIL, PT, PTT, Plasma aminoacid HPLC, Homocysteine, Urine aminoacid and carbohydrate chromatography, Acyl carnitine profile, urine organic acids and for next steps tissue specimen and enzyme activity and gene study.clinical chemical indices of organid aciduria is Metabolic acidosis, Increased anion gap, Hyperglycemia and hypoglycemia, Ketosis and Ketonuria, Lactic acidosis, Hyperammonemia, Hyperuricemia, Hypertriglyceridemia, increase of transaminase Granulocytopenia, thrombocytopenia and Anemia. Acylcarnitine profile and urine organic acids are two for important tests for differentiation of types oforganic academia.

Immidiate ManagementInfants and children with acute metabolic crisis require immediate treatment to prevent further acute deterioration and long-term sequelae.Early and appropriate treatment before confirmation of the diagnosis is life-saving.Eliminate intake of the precursors of possibly toxic metabolites.This applies most often to suspected inborn errors of amino acid or organic acid metabolism. In both cases, dietary or parenteral intake of protein and amino acids should be eliminated immediately an organic acidemia is suspected.Administer glucose a simple source of calories at least 8 mg / kg / min to suppress mobilization of endogenous sources of the metabolites.This is achieved by the intravenous administration of 10% dextrose supplemented by Intralipid.Specific TherapydiseaseNPO: Minimize intake and endogenous productionof toxic metabolites.Hadration: Administer high-calorie, high-carbohydrate intravenousfluids: 10% dextrose in 0.2% NaCl at 1.5 times calculated maintenance, and add KCl. Alkali Therapy: Bicarbonate is generally not indicated unless the plasma bicarbonate is <10 mmol/L; deficits should be only half corrected.Hemo or peritoneal dialysis: If just described measures fail to induce clinical & biochemical improvement, hemo or peritoneal dialysis is indicated to Accelerate elimination of toxic metabolites. If hyperammonemia exists:1.5 × Maintenance D/W 10 % & intravenous lipids 1 g/kg 24 hSodium benzoate 250 mg/ kg to be added to 20 cc/kg of 10% glucose & infused within 1-2 h (priming dose) Continue infusion of sodium benzoate 250-500 mg / kg / 24 h following the above priming dose & should be added to daily intravenous fluidsInitiate peritoneal dialysis or hemodialysis: if above treatment fails to produce an appropriate decrease in plasma ammonia.Peritoneal dialysis is too slow. Exchange transfusion brings the plasma ammonium down quickly, but rebound hyperammonemia occurs just as quickly.It may be useful in some circumstances as an adjunct to hemodialysis.

Clinical differential DiagnosisThe organic acidemias are important in the differential diagnosis of metabolic and neurologic derangement in the neonate and of new-onset neurologic signs in the older child.A-Organic aciduriaSeveral disorders, not classified as primary disorders of organic acid metabolism, have a characteristic urinary organic acid profile that suggests the appropriate diagnosis.• Mevalonicaciduria, a disorder of cholesterol biosynthesis, shows mevalonic acid in the urine.• Glutaricacidemia type II, a disorder of fatty acid oxidation, has multiple organic acids in abnormal concentration in urine. These organic acids include ethylmalonic acid, glutaric acid, dicarboxylic acids, and glycine conjugates of medium chain dicarboxylic acids.• The fatty acylCoA-glycine conjugates that signal incomplete fatty acid oxidation and serves as signals to the diagnosis of MCAD defeciency and other disorders of fatty acid oxidation and transport.• Biotinidase deficiency, a disorder of biotin recycling, results in the urinary excretion of several unusual organic acids, including 3-hydroxy-isovaleric, 3-hydroxypropionic, 3-hydroxybutyric acids, and acetoacetate. Propionyl glycine may also be seen.• Mitochondrial diseases with disordered oxidative phosphorylation often demonstrate the presence of abnormal organic acids in the urine.B-AcidosisNon-genetic conditions, such as shock, sepsis, DKA, liver and kidney failure, thiamine deficiency, RTA, some drug intoxication cause acidosis- genetic conditions are include: inherited metabolic disorders of lactate and pyruvate metabolism and oxidative phosphorylation, disorders of the Krebs cycle such as fumarase deficiency.C-HyperammonemiaDisorders of the urea cycle and the hyperammonemia-hypoglycemia syndrome.Neuroimaging• A variety of MRI abnormalities have been described in the organic academia, including distinctive basal ganglia lesions in glutaricacidemia type I (GA I), white matter changes in maple syrup urine disease (MSUD), and abnormalities of the globus pallidus in methylmalonic acidemia. Macrocephaly is common in GA I.• Some differential agnosis of MRI findings in organic academia is consist of: HIE, mucopolysacaridosis, middle fossa arachnoid cyst, leighdisease, hexachlorophene toxicity in neonates, myelin splitting disorders.• Some organic aciduria such as L-2-Hydroxyglutaricaciduria may suggest leukodystrophy in MRI.

ObjectiveGlutaric aciduria type 1 (GAL 1) is a cerebral organic academia, which manifests as encephalopathy with long-term neurological handicap. In this study, clinical presentation, neuroimaging, molecular finding of CGDH mutation of our patients were reviewed.Materials and MethodsThis was a descriptive and cross-sectional study. Patients in whom GLA1 were suspected by clinical manifestation, neuroimaging or metabolic study during last 10 years (2001-2011) in pediatric Mofid hospital were tested for CGDH gene mutation. ResultsPatients age range at study times were 15-102 months. Patients’ ages at diagnosis time were 5-17 months. All of parents of our patients were relative. Clinical presentation in order were: developmental delay (54%), macrocephaly and seizure (45%), dystonia (36%), neurodevelopmental regression (27%), acute encephalopathy after fever and vaccination (18%). Neuroimaging finding in brain CT scan and MRI in majority of patients included brain atrophy, widely open sylvian fissure and basal ganglia calcification. Enzymatic study was not performed. Molecular testing results of CGDH in all patients were abnormal. A new mutation in CGDH was detected in our patients.ConclusionGLA1 has a protean clinical presentation with different neurological sequel. It is essential to detect patients by newborn screening. Molecular testing and enzymatic study of CGDH activity establish the diagnosis of patients and prenatal diagnosis, too.

Organic acidemias are the group of metabolic disorders which define by high anion gap metabolic acidosis, hypo or hyperglycemia & hyperammonemia.Because of the severity of disease in children and its fatality in severe form of disease and also need for life long treatment, prenatal diagnosis is an important diagnostic tool.Three approaches to prenatal diagnosis may be possible, including measurement of analytes in amniotic fluid or use of cells obtained by Choronic Villus sampling (CVS) or amniocentesis to either assay enzyme activity or extract DNA for molecular genetic testing.Biochemical genetic testing: Prenatal diagnosis for pregnancies at increased risk for propionic acidemia, methylmalonic acidemia, biotin-unresponsive3-methylcrotonyl-CoA carboxylase deficiency, glutaric acidemia type 1, ketothiolase deficiency, methylmalonic aciduria and homocystinuria, cblC type, and isovaleric acidemia is possible by analysis of amniotic fluid if highly accurate quantitative methods are used to measure the appropriate analytes. Amniocentesis is usually performed at approximately 15 to 18 weeks gestation.Prenatal diagnosis for pregnancies at increased risk for MSUD is possible by measurement of enzyme activity in fetal cells obtained by chorionic villous sampling(CVS) at approximately ten to 12 weeks gestation or amniocentesis usually performed at approximately 15 to 18 weeks gestation.(If cells from CVS are used, extreme care must be taken to assure that they are fetal rather than maternal cells).Molecular genetic testing:Prenatal diagnosis for pregnancies at increased risk for all disorders is possible by analysis of DNA extracted from fetal cells obtained by amniocentesis usually performed at approximately 15 to 18 weeks of gestation or chorionic villous sampling (CVS) at approximately ten to 12 weeks of gestation. Both disease-causing allels of an affected family member must be identified before prenatal testing.Preimplantation genetic diagnosis (PGD) may be available for families in which the disease causing mutation has been identified.

Glutaric Acidemia, Type I (GA I), was first described in 1975. The disease is caused by a genetic deficiency of the enzyme, Glutaryl-CoA Dehydrogenase (GCD), which leads to the buildup of Glutaric acid in the tissues and its excretion in the urine of affected patients. GCD is involved in the catabolism of the amino acids, Lysine, Hydroxylysine, and Tryptophan. Over 200 cases of GA I have been reported in the medical literature. GA I is one of the most common organic acidemias and has an estimated incidence of about 1 in 50,000 live births.Because of the initial slow progression of clinical symptoms, GA I is frequently undiagnosed until an acute metabolic crisis occurs. A total of 25 unrelated patients suspected to GA1 were investigated in our study. Genomic DNA was extracted from peripheral blood cells of the 25 probands whom were biochemically and/or clinically and/or neuro-radiologically suspected to GA1. 15 of them had elevated glutaric acid in the urine organic acid test.PCR and direct sequencing of all 11 exons and their flanking region of the GCDH gene were examined.Some of them were investigated for known mutation in the other their family members. Fifteen patients had homozygous mutations and 10 patients were normal for GCDH gene. Our Results Showed:

Organic academia are diverse group of disorders characterized by abnormal degredation of specific amino acid in the specific catabolism due to an enzymeactivity defect which mainly due to enzyme deficiency. The majority of the classic organic acid disorders are caused by abnormal catabolism of branched-chain amino acids like lysine. maple syrup urine disease (MSUD), propionic acidemia, methylmalonic acidemia (MMA), Ethylmalonic academia,glutaricacidemia type I and so on. The most common presentation is related to toxic encephalopathy which are as follows: vomiting, poor feeding,neurologic symptoms such as seizures and abnormal tone, and lethargy progressing to coma and the outcome may be loss of intellectual function, ataxia, psychiatric symptoms and other neurological deficit.Along with laboratory tests, Imaging have some characteristic findings in determination of these wide range of disease and can help in categorization and differentiation these form of brain metabolic disorders in conjunction by other investigative study. In this lecture trying to review imaging findings of more common organic academia in children will be done.