Clinical, biochemical and molecular characterization of 12 patients with pyruvate carboxylase deficiency treated with triheptanoin

Pyruvate carboxylase (PC) deficiency is a rare autosomal recessive mitochondrial neurometabolic disorder of energy deficit resulting in high morbidity and mortality, with limited therapeutic options. The PC homotetramer has a critical role in gluconeogenesis, anaplerosis, neurotransmitter synthesis, and lipogenesis. The main biochemical and clinical findings in PC deficiency (PCD) include lactic acidosis, ketonuria, failure to thrive, and neurological dysfunction. Use of the anaplerotic agent triheptanoin on a limited number of individuals with PCD has had mixed results. We expand on the potential utility of triheptanoin in PCD by examining the clinical, biochemical, molecular, and health-related quality-of-life (HRQoL) findings in a cohort of 12 individuals with PCD (eight with Type A and two each with Types B and C) treated with triheptanoin ranging for 6 days to about 7 years. The main endpoints were changes in blood lactate and HRQoL scores, but collection of useful data was limited to about half of subjects. An overall trend of lactate reduction with time on triheptanoin was noted, but with significant variability among subjects and only one subject reaching close to statistical significance for this endpoint. Parent reported HRQoL assessments with treatment showed mixed results, with some subjects showing no change, some improvement, and some worsening of overall scores. Subjects with buried amino acids in the pyruvate carboxyltransferase domain of PC that undergo destabilizing replacements may be more likely to respond (with lactate reduction or HRQoL improvement) to triheptanoin compared to those with replacements that disrupt tetramerization or subunit-subunit interface contacts. The reason for this difference is unclear and requires further validation. We observed significant variability but an overall trend of lactate reduction with time on triheptanoin and mixed parent reported outcome changes by HRQoL assessments for subjects with PCD on long-term triheptanoin. The mixed results noted with triheptanoin therapy in this study could be due to endpoint data limitation, variability of disease severity between subjects, limitation of the parent reported HRQoL tool, or subject genotype variability. Alternative designed trials and more study subjects with PCD will be needed to validate important observations from this work.

Unsuccessful treatment of severe pyruvate carboxylase deficiency with triheptanoin

Pyruvate carboxylase (PC) deficiency (OMIM 266150) is an autosomal recessive disorder that usually presents with lactic acidaemia and severe neurological dysfunction, leading to death in infancy. Because the enzyme is involved in gluconeogenesis and anaplerosis of the Krebs cycle, therapeutic strategies have included avoiding fasting and attempts to correct the defect of anaplerosis. Triheptanoin is a triglyceride of C7 fatty acids. The oxidation of odd chain fatty acids leads to the production not only of acetyl-CoA but also of propionyl-CoA, which is an anaplerotic substrate for the Krebs cycle. One infant with PC deficiency has previously been treated with triheptanoin as well as citrate and 2-chloropropionate. We report two further patients with PC deficiency, who were treated with triheptanoin, continuously from 11 and 21 days of age. They were also given citrate, aspartate and dichloroacetate. Triheptanoin did not lead to any clinical or biochemical improvement. The plasma and CSF lactate concentrations remained high with episodes of severe ketoacidosis and lactic acidosis. Both patients had severe hearing loss, roving eye movements, seizures and very limited neurodevelopmental progress; they died at the ages of 7 and 8 months.

CONCLUSION

Though triheptanoin did not alter the clinical course in our patients, it was well tolerated. It remains possible that less severely affected patients might benefit from this form of therapy.

Pyruvate carboxylase deficiency--insights from liver transplantation

Pyruvate carboxylase deficiency, complex form, presents in early infancy with lethal metabolic acidosis, resulting from ketoacidosis and lactic acidemia. Renal tubular acidosis, hyperammonemia, and citrullinemia complete the picture. In an infant with this disease, large amounts of glucose ameliorated the ketoacidosis, but worsened the lactic acidosis. Orthotopic hepatic transplantation completely reversed the ketoacidosis and the renal tubular abnormality and ameliorated the lactic acidemia. Concentrations of glutamine in cerebrospinal fluid were low and did not improve with liver transplantation.

Treatment of pyruvate carboxylase deficiency with high doses of citrate and aspartate

A patient with severe pyruvate carboxylase deficiency presented at age 11 weeks with metabolic decompensation after routine immunization. She was comatose, had severe lactic acidemia (22 mM) and ketosis, low aspartate and glutamate, elevated citrulline and proline, and mild hyperammonemia. Head magnetic resonance imaging showed subdural hematomas and mild generalized brain atrophy. Biotin-unresponsive pyruvate carboxylase deficiency was diagnosed. To provide oxaloacetate, she was treated with high-dose citrate (7.5 mol/kg(-1)/day(-1)), aspartate (10 mmol/kg(-1)/day(-1)), and continuous drip feeding. Lactate and ketones diminished dramatically, and plasma amino acids normalized, except for arginine, which required supplementation. In the cerebrospinal fluid (CSF), glutamine remained low and lysine elevated, showing the treatment had not normalized brain chemistry. Metabolic decompensations, triggered by infections or fasting, diminished after the first year. They were characterized by severe lactic and ketoacidosis, hypernatremia, and a tendency to hypoglycemia. At age 3(1/2) years she has profound mental retardation, spasticity, and grand mal and myoclonic seizures only partially controlled by anticonvulsants. The new treatment regimen has helped maintain metabolic control, but the neurological outcome is still poor.

MRI, clinical, and biochemical features of partial pyruvate carboxylase deficiency

We report a boy with a partial deficiency of pyruvate carboxylase as documented in enzyme assays of skin fibroblasts, lymphocytes, and hepatic tissue. Magnetic resonance imaging at age 20 months demonstrated a leukodystrophic process involving the brain stem and subcortical white matter, which, except for the brain stem, improved after biotin treatment. The lymphocyte pyruvate carboxylase activity of both heterozygous parents slightly increased after receiving oral biotin for 1 month, but a definitive enzymatic response to biotin was not confirmed in our patient. At age 6 years, he is dysarthric with a spastic quadriparesis despite improvements in development and myelination. This is the first demonstration of magnetic resonance imaging changes in this disease.