Short Communication Biol Neonate 2006;90:207–209 DOI: 10.1159/000093590
Received: December 5, 2005 Accepted after revision: February 20, 2006 Published online: May 29, 2006
Normal Serum Alanine Concentration Differentiates Transient Neonatal Lactic Acidemia from an Inborn Error of Energy Metabolism Eva Morava a Marije Hogeveen a Maaike De Vries a Wim Ruitenbeek a, b Willem-Pieter de Boode a Jan Smeitink a a
Department of Pediatrics, b Laboratory of Pediatrics and Neurology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
Key Words Neonatal asphyxia Transient lactic acidemia Alanine Mitochondrial dysfunction
Abstract Background: Elevated blood lactate levels are common in the critically ill neonate; however, sometimes they are difficult to interpret. Persistent or recurrent lactic acidemia might point to an inborn error of metabolism, like disturbances of the oxidative phosphorylation. Chronic lactic acidemia results in increased serum alanine levels. Serum alanine levels in newborns with transient lactic acidemia have not yet been studied. Objective: We designed a pilot study to evaluate the use of serum alanine levels as an additional metabolic marker to differentiate the transient effect of circulatory failure from a possible mitochondrial dysfunction. Methods: We prospectively evaluated 10 newborns with transient lactic acidemia after mild dysoxia, and 10 newborns with recurrent lactic acidemia consecutively diagnosed with a disorder in oxidative phosphorylation. Results: No significant serum alanine level elevation was found in transient lactic acidemia. Increased serum alanine was a sensitive marker in mitochondrial dysfunction. Conclusions: We propose to measure the serum alanine level in hypotonic newborns with lactic acidemia to facilitate the decision making in further diagnostics and management. Copyright © 2006 S. Karger AG, Basel
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Introduction
Repeatedly high blood lactate concentrations are commonly present in critically ill neonates, for example after asphyxia, but might also point to an inborn error of metabolism. After ruling out a cardiac anomaly, sepsis or renal dysfunction, it is important to differentiate between transient lactate elevations due to dysoxia, inherited metabolic disorders and disturbances of the oxidative phosphorylation system [1–3]. When the initial clinical presentation in newborns with lactic acidemia is nonspecific, the use of an additional metabolic marker is beneficial in differentiating the effect of decreased oxygen delivery from a possible mitochondrial dysfunction. Increased serum alanine levels are commonly measured in individuals with chronic lactic acid elevations [3, 4]. Lactate, pyruvate and alanine have a biochemical balance in serum due to the activity of the enzymes alanine aminotransferase and lactate dehydrogenase. The mitochondrial and cytosolic alanine aminotransferase isozymes provide pyruvate from alanine for the further metabolism in the mitochondrial compartment by decarboxylation [5]. Hypoxic ischemia in animal models leads to a depletion of tissue ATP and glucose with an accumulation of lactic acid and alanine [6, 7]. Seizures due to hypoxic brain injury result in transient elevation of lactic acid, alanine and glutamate in neonatal rats [8]. Lactic
Eva Morava, MD, PhD Department of Pediatrics, Nijmegen Centre for Mitochondrial Disorders Radboud University Nijmegen Medical Centre, PO Box 9101 NL–6500 HB Nijmegen (The Netherlands) Tel. +31 24 361 9470, Fax +31 24 361 6428, E-Mail
[email protected]
Table 1. Blood lactate and parallel measured serum alanine levels in neonates with lactic acidemia: transient
lactate elevations (group 1), recurrent/chronic lactic acidemia and mitochondrial dysfunction (group 2) Group 1
Group 2
patient
blood lactate mmol/l
serum alanine mol/l*
1 2 3 4 5 6 7 8 9 10 Mean8SEM
3.2 2.8 3.2 3.0 3.4 2.2 2.3 2.8 2.6 2.8 2.880.1
275 343 185 266 220 304 280 312 385 420 299822
patient
1 2 3 4 5 6 7 8 9 10 Mean8SEM
mutation
blood lactate mmol/l
serum alanine mol/l*
8993T/G (mtDNA) C175T /C1268T NDUFV1 8993T/C (mtDNA) 8993T/G (mtDNA) G364A /G364A, NDUFS7 Ex5 G370A, SURF1 8993T/G (mtDNA) 8993T/C (mtDNA) 8993T/G (mtDNA) C175T /C1268T, NDUFV1
2.8 4.8 2.8 2.5 2.2 3.8 2.2 6.4 3.3 2.8 3.380.3
552 680 515 495 410 780 310 610 455 600 542825
Serum alanine levels are significantly different, * p < 0.001.
acidosis and a marked increase in serum alanine concentrations have also been described in association with sepsis [9]. Young infants of HIV-infected mothers exposed to nucleoside analogues frequently develop reversible lactic acidemia with the elevation of serum alanine concentration [10]. Serum alanine levels in newborns with transient lactic acidemia have not yet been studied.
Patients and Methods In order to compare the level of lactic acid in blood and serum alanine levels in transient and in chronic/recurrent lactic acidemia, we performed a prospective pilot study (table 1). We included 10 newborns with neonatal dysoxia (umbilical cord blood pH ! 7.0, Apgar scores ! 7 5 min after delivery, no resuscitation, no signs of encephalopathy or multiorgan failure), showing lactic acid elevations in the first 2 days of life. They were compared with 10 children with neonatal lactic acid elevations and a later confirmed recurrent lactic acidemia, consecutively diagnosed with a disorder in oxidative phosphorylation (isolated complex I, IV or complex V deficiency measured in a fresh muscle biopsy, and known DNA mutations). Blood lactate levels were measured daily in both groups in the neonatal period. Transient lactic acidemia was defined as consecutively measured lactic acid concentrations above 2.1 mmol/l for a period of 3–8 days after birth with spontaneous resolution. Chronic/recurrent lactic acid elevation was defined as lactic acid concentrations above 2.1 mmol/l measured in blood in the neonatal period and further at least on two occasions (in a period longer than 1 year). Lactic acid measurements were performed
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from arterial blood samples obtained from a canulated blood vessel. The initial samples were taken daily in the first 8 days of life in both patient groups. The measurement was repeated at the time of discharge as well. Blood lactate samples were delivered on ice to the laboratory. Serum amino acids including serum alanine levels were measured in all patients between the 3rd and 8th day of life using an amino acid analyzer by standard methods in fresh venous blood samples. The lactic acid levels measured in blood parallel with the alanine level are demonstrated on table 1. Except for the lactic acidemia no other metabolic alteration, no metabolic acidosis, or hypoglycemia was observed in the children studied. All patients had normal birth parameters for weight, height and head circumference. All neonates underwent a clinical evaluation to rule out congenital malformations, cardiac dysfunction (assessed by ECG and echocardiogram) and to rule out liver and renal dysfunction. Sepsis workup was negative. No congenital infection was confirmed. No special diet was applied. The patients received no bicarbonate supplementation. The neonates were controlled after 3 months and 1 year at our Department of Pediatrics. No significant alteration in the psychomotor development was noted in the ‘dysoxic’ group. The neonates with recurrent lactate elevations were followed at our metabolic unit for a period longer than 1 year. Consecutive lactate and amino acid sampling was done at the outpatient clinics. The data of the two groups were expressed as means 8 standard error of the mean (SEM). Between-group differences were statistically analyzed using one-way analysis of variance followed by the Scheffé post-hoc test when appropriate. For these statistical analyses, the SPSS package software (version 12.0.1) was used. Double-sided p values ! 0.05 were considered statistically significant.
Morava /Hogeveen /De Vries /Ruitenbeek / de Boode /Smeitink
Results
In the group of patients with transient lactate elevations, blood lactic acid levels were detected between 2.2– 3.4 mmol/l up to the 3rd day of life (normal !2.1). All patients had normal serum alanine levels (controls: 150– 450 mol/l, table 1). The lactic acidemia resolved after the 5th to the 8th day of life. In the patient group with mitochondrial dysfunction, the blood lactic acid levels were 2.2–6.4 mmol/l. Eight out of the 10 patients had elevated serum alanine concentrations (table 1). Nonparametric statistical analysis demonstrated a significant difference in alanine levels between the neonatal group and the patients with oxidative phosphorylation disorders (p = 0.001). No significant difference was observed in the blood lactic acid concentrations between the two groups of patients.
Discussion
Disorders of the oxidative phosphorylation should be considered in the differential diagnosis of neonatal muscle hypotonia with variable associated symptoms, especially with serum lactic acid elevations. In most patients with a respiratory chain disease and severe neonatal lactic acidosis, the diagnosis is established early due to the dramatic clinical presentation and rapidly progressive clinical course. Severe encephalomyopathy, seizures and feeding problems might additionally increase the lactate and alanine levels in neonates with other types of mito-
chondrial dysfunction, like pyruvate dehydrogenase defect. In our small pilot study group, however, all included patients with hypotonia had relatively mild lactic acidemia without other clinical symptoms; therefore, the clinical examination was not distinctive in ruling out a possible inborn error. No significant serum alanine level elevation was present in blood in neonates with transient lactic acidemia; however, increased serum alanine was a sensitive marker in most patients (except for patient 7) with mitochondrial dysfunction and chronic/recurrent lactic acidemia. Since our group of patients was genetically relatively homogeneous, the relevance of our results should be confirmed in more patients with different types of respiratory chain deficiency. Glutamine levels are frequently used to monitor chronic hyperammonemia in children with urea cycle disorders. We propose to use the measurement of serum alanine levels in hypotonic newborns with lactic acidemia in order to obtain an additional means of differentiating the effects of dysoxia from a possible mitochondrial disorder. Furthermore, we suggest developing of a simple bedside alanine test in order to facilitate the diagnostic workup of patients suspected to suffer from a mitochondrial disorder. Acknowledgements This work was supported by the European Community’s Sixth Framework Program for Research, Priority 1 ‘Life sciences, genomics and biotechnology for health’ (contract LSHM-CT-2004503116).
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Normal Alanine in Transient Lactic Acidemia
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