Cerebral Developmental Abnormalities in a Mouse with Systemic Pyruvate Dehydrogenase Deficiency

Pyruvate dehydrogenase (PDH) complex (PDC) deficiency is an inborn error of pyruvate metabolism causing a variety of neurologic manifestations. Systematic analyses of development of affected brain structures and the cellular processes responsible for their impairment have not been performed due to the lack of an animal model for PDC deficiency. METHODS: In the present study we investigated a murine model of systemic PDC deficiency by interrupting the X-linked Pdha1 gene encoding the α subunit of PDH to study its role on brain development and behavioral studies. RESULTS: Male embryos died prenatally but heterozygous females were born. PDC activity was reduced in the brain and other tissues in female progeny compared to age-matched control females. Immunohistochemical analysis of several brain regions showed that approximately 40% of cells were PDH⁻. The oxidation of glucose to CO₂ and incorporation of glucose-carbon into fatty acids were reduced in brain slices from 15 day-old PDC-deficient females. Histological analyses showed alterations in several structures in white and gray matters in 35 day-old PDC-deficient females. Reduction in total cell number and reduced dendritic arbors in Purkinje neurons were observed in PDC-deficient females. Furthermore, cell proliferation, migration and differentiation into neurons by newly generated cells were reduced in the affected females during pre- and postnatal periods. PDC-deficient mice had normal locomotor activity in a novel environment but displayed decreased startle responses to loud noises and there was evidence of abnormal pre-pulse inhibition of the startle reflex. CONCLUSIONS: The results show that a reduction in glucose metabolism resulting in deficit in energy production and fatty acid biosynthesis impairs cellular differentiation and brain development in PDC-deficient mice.

[Pyruvate dehydrogenase deficit associated to the C515T mutation in exon 6 of the E1alpha gene]

INTRODUCTION

Pyruvate dehydrogenase (PDH) deficiency constitutes the most frequent metabolic origin of congenital lactic acidosis and is also responsible for a less usual form, found exclusively in females, which leads to a dysmorphic syndrome accompanied by severe cerebral malformations. The most common defect affects fraction E1alpha (gene Xp22.1-22.2).

AIM

To report the case of a young female with PDH deficiency, dysmorphic syndrome, cerebral deformations and an unidentified mutation in the corresponding gene.

CASE REPORT

An 8-month-old female with microcephaly, a narrow forehead, nasal hypoplasia, anteverted nostrils, thin lips, axial hypotonia, epileptic seizures and an umbilical hernia. Magnetic resonance imaging of the brain revealed intense supra- and infratentorial cortico-subcortical atrophy, ventricular dilatation and agenesis of the corpus callosum. Lactic and pyruvic acid concentrations were high both in blood and in cerebrospinal fluid (CSF), and the level of alanine was high in CSF. Muscular histology results were normal. PDH complex activity in fibroblasts and in muscle tissue, as well as that of the mitochondrial respiratory chain complexes in muscle homogenate, were found to be normal. A molecular genetic study of the gene for PDHE1alpha, both in formed elements in the blood and in fibroblasts, showed a C > T change in nucleotide 515 (C515T) of exon 6, which causes a P172L change in the protein. A study of 108 controls ruled out the possibility of a polymorphism. The parents did not have the mutation.

CONCLUSIONS

The C515T mutation of exon 6 of the gene for PDH E1alpha is described. Normal activity of the PDH complex in fibroblasts and in muscle tissue does not exclude this condition.

Continuous pH monitoring using the Paratrend 7 inserted into a peripheral vein in a patient with shock and congenital lactic acidosis

The authors present a 25-year-old woman who was admitted to the ICU for treatment of shock, respiratory failure, and acidosis related to congenital lactic acidosis from pyruvate dehydrogenase deficiency. To aid in ongoing management of the metabolic acidosis, the Paratrend blood gas monitoring sensor was inserted through a peripheral venous site to provide a continuous measurement of pH and partial pressure of carbon dioxide (Pco2). With the venous insertion of the Paratrend, a clinically useful correlation with arterial blood gas values was noted. Linear regression analysis of the pH values from the venous blood gas analyses and the Paratrend monitor revealed r2 = 0.71 with p = 0.001 and r2 = 0.78 with a p = 0.0003 for the Pco2 values. Our preliminary experience suggests that venous placement of the Paratrend monitor can be used to provide clinically useful, continuous measurement of pH and Pco2.

Concomitant administration of sodium dichloroacetate and thiamine in west syndrome caused by thiamine-responsive pyruvate dehydrogenase complex deficiency

We treated a female patient with West syndrome caused by thiamine-responsive pyruvate dehydrogenase complex (PDHC) deficiency. Infantile spasms occurred in association with elevated blood and CSF lactate concentrations; these symptoms disappeared when lactate concentrations had been lowered by treatment with concomitant sodium dichloroacetate (DCA) and high dose thiamine. Sequencing the patient's PDHC E(1)alpha subunit revealed a substitution of serine for glycine at position 89 in exon 3 (G89S). This mutation must be a de novo mutation because it was not found in either parents' genome DNA. To our knowledge, five previously described patients with PDHC deficiency have displayed the West syndrome. All six known patients, including our own, were female, even though an approximately equal number of males and females have been identified with PDHC deficiency and overall West syndrome occurs somewhat more frequently in males. These results indicated that West syndrome occurred more frequently in female patients with PDHC deficiency. It is suggested that lactate concentration should be measured in patients with West syndrome for potential PDHC deficiency, especially in females.

Adult leigh syndrome: treatment with intravenous soybean oil for acute central respiratory failure

This study reports a 38-year-old woman with adult Leigh syndrome associated with partial deficiency of the pyruvate dehydrogenase complex. The patient had intermittent diplopia, loss of vision, dystonia, central respiratory failure and unconsciousness with lactic acidosis. Treatment with an intravenous ketogenic emulsion resulted in rapid clinical and biochemical improvement. In patients with acute respiratory failure under these circumstances, intravenous ketogenic emulsion therapy is worth consideration.

Deficiency of pyruvate dehydrogenase complex in tissues of an eight month old infant

A metabolic investigation was carried out in an eight-month old infant with intrauterine hypotrophia, failure to thrive, psychomotoric retardation and cerebral atrophy, who died after respiratory infections. Blood analysis revealed intermittent lactic acidosis with normal lactate/pyruvate ratio. Activities of cytochrome c oxidase in skeletal muscle, heart, liver and fibroblasts were all in the reference range of controls. Activity of pyruvate dehydrogenase complex (PDH) was decreased in muscle homogenate, heart and liver mitochondria but was normal in cultured skin fibroblasts. Immunodetection of PDH subunits, and assay of El alpha phosphorylation showed in the patient decrease of E1 alpha in skeletal muscle, and enhanced level of E1 alpha phosphorylation in liver mitochondria.

Neurodevelopmental abnormalities and lactic acidosis in a girl with a 20-bp deletion in the X-linked pyruvate dehydrogenase E1 alpha subunit gene

We describe a girl with developmental abnormalities of the CNS and a lactic acidosis whose cultured fibroblasts showed a profound deficiency of pyruvate dehydrogenase complex (PDHC) activity (patient = 0.14 nmol/mg protein per minute, controls = 0.7 to 1.1 nmol/mg protein per minute). Immunocytochemistry demonstrated the fibroblast culture to be mosaic, with 14% of cells expressing the PDHC E1 alpha subunit protein in normal amounts and the remaining 86% having no detectable immunoreactive activity. Direct sequencing of cDNA for the X-linked PDHC E1 alpha subunit established that the patient was heterozygous for a 20-bp deletion beginning in the codon for Ser300 of the derived amino acid sequence. The pattern of methylation at the DXS255 locus suggested predominant expression of the X chromosome carrying the mutant allele in the fibroblast culture. There was a good correlation between the residual PDHC activity, the proportion of cells with immunoreactive E1 alpha protein, and the X chromosome inactivation ratio, demonstrating the importance of X-inactivation for expression of this X-linked neurometabolic disease in females.

Metabolic myopathies: evaluation by graded exercise testing

Exertional muscle pain and fatigue are common complaints; some patients with these symptoms have a metabolic myopathy. We have performed graded exercise testing with analysis of expired ventilation on 13 individuals with various kinds of metabolic myopathies. Their results differed from normal and reflected the underlying biochemical abnormality. Patients with disorders of the mitochondrial electron transport chain demonstrated marked limitations in aerobic metabolism and a greatly reduced maximum oxygen consumption. During intense exertion, normal individuals increase carbon dioxide generation due to buffering of lactic acid. This did not occur in patients with McArdle disease, in whom the respiratory exchange ratio (carbon dioxide production/oxygen consumption) did not rise above 1.0 at maximum exercise. These results indicated a deficit in anaerobic metabolism. Pyruvate dehydrogenase complex allows pyruvate produced from carbohydrate metabolism to enter the citric acid cycle. Patients with this enzyme deficiency showed an initially normal pattern followed by an abrupt cessation in carbohydrate dependent aerobic metabolism at higher work loads. During high-intensity exercise, progressive anaerobic metabolism was not accompanied by additional oxygen consumption. Finally, results from a patient with carnitine palmitoyl transferase deficiency revealed an early dependence on carbohydrate metabolism. The ventilatory threshold occurred at a low percentage of maximal oxygen consumption, reflecting the limited availability of lipid substrates for aerobic metabolism. Detection of some muscle metabolic abnormalities can be made on small biopsy specimens. However, definitive diagnosis of the defect nearly always requires studies on fresh or frozen muscle tissue obtained by an open biopsy. The decision on how the tissue should be processed and which metabolic studies should be performed frequently needs to be made before the biopsy is obtained. Thus, a noninvasive method to initially characterize patients with potential metabolic disorders is useful. Exercise testing with expired gas analysis can indicate the presence of a metabolic myopathy and results can then be used to direct the appropriate biochemical evaluations.