Introduction
Propionic Acidemia (PA, OMIM #606054) is one of the intoxication type organic acidemias which often present in the neonatal period with lethargy, poor feeding, and vomiting and can progress to coma if not identified and treated appropriately.1 Inborn errors of metabolism can have a severe impact on human health, so comprehensive diagnostic neonatal screening is used for early diagnosis to avoid potentially catastrophic physical and neurological effects. These defects can cause a build-up of toxic metabolites, resulting in serious, often fatal, disease early in life. Neonatal blood screening with mass spectrometry (MS) is now commonly used to test new-borns for a wide array of inborn errors of metabolism using specific metabolites for diagnosis. PA results from a defect in the enzyme propionyl-CoA carboxylase, which catalyses the biotin-dependent conversion of propionyl-CoA to methylmalonyl-CoA. MMA results from deficiency of the immediately downstream enzyme methylmalonyl-CoA mutase, which catalyses the vitamin B12-dependent conversion of methylmalonyl- CoA to succinyl-CoA. Patients have considerable variability in symptoms and clinical prognosis, which are correlated with genetic locus.
Materials and Methods
The Institutional Human Ethical committee approval is from Madras Medical College, Chennai: Approval No. 32042018 and was obtained consent form from parents for the participation of this research study. Liquid Chromatography -Mass Spectrometry Analysis (LC-MS/MS) was done at metabolic lab, Department of biochemistry, at Institute of child health and hospital for children, Chennai.
Algorithm: Hyperammonaemia (>200 µmol/L)
Increased anion gap >25 mmol/L, Urine ketone positive leads to organic aciduria’s.
Respiratory alkalosis, increased plasma citrulline or urine oxalate increase leads to urea cycle disorder.
Characteristic Urine smell, Urine DNPH test positive with abnormal amino acid profile leads to amino acid disorder
Premature baby with respiratory distress in the first day of life leads to transient Hyperammonemia.
Biochemical findings in propionic acidemia include: Common laboratory abnormalities during acute decompensation include: High-anion gap metabolic acidosis, Lactic acidosis, elevated plasma and urinary ketones, Low to normal blood glucose concentration, Hyperammonemia, Neutropenia, anemia, and thrombocytopenia.
Plasma acylcarnitine profile: Elevated propionyl carnitine (C3)
Urine organic acids: Elevated 3-hydroxypropionate Presence of: Methyl citrate, Tiglylglycine, Propionyl glycine, Lactic acid.
Plasma amino acids: Elevated glycine.
Metabolic pathways
Propionyl CoA precursors include isoleucine, threonine, methionine, valine and odd chain fatty acids, and cholesterol side chains. Deficient in propionyl -CoA-carboxylase activity is the enzyme defect between propionyl CoA and methyl malonyl CoA production. With biotin supplementation it inhibits the urea cycle and citric acid. Those are metabolites involved in the 3-OH propionic acid, 3-methyl citrate, and propionyl carnitine deficiency of this enzyme which were elevated in the blood. In propionic acidemia the biochemical effect is increased organic acids which lead to ketosis and metabolic acidosis with secondary hyperammonemia and hyperglycinemia. OA are all inherited autosomal-recessive disorders mainly affecting degradation of branched-chain amino acids. Hyperammonaemia is attributable to the decrease in and inhibition by toxic metabolites of acetyl coenzyme A (CoA) from NAGS and CPS1 activities. Hyperammonaemia in these diseases is accompanied by severe metabolic acidosis with high gap in anions and ketonuria. The diagnosis is made by chromatography of urinary organic acid and the acylcarnitine profile of the plasma.
Catalytic activity and function
Protein: Propionyl-CoA carboxylase alpha chain, mitochondrial (PCCA)[EC:6.4.1.3] A biotinyl-protein. Also carboxylates butanoyl-CoA and catalyses transcarboxylation. Reaction:
ATP + hydrogen carbonate + propionyl-CoA = (S)-methyl malonyl CoA + ADP + H+ + phosphate
Protein: Propionyl-CoA carboxylase beta chain (PCCB) [EC:6.4.1.3 2.1.3.15] (acetyl CoA Carboxy transferase) Reaction:
[biotin carboxyl-carrier protein]-N6-carboxybiotinyl-L-lysine + acetyl-CoA = [biotin carboxyl-carrier protein]-N6-biotinyl-L-lysine + malonyl-CoA.
Clinical description
Phenotype varies from severe neonatal-onset forms with high mortality and poor outcome with a later onset to milder forms. In both cases the risk of relapses from life-threatening episodes of metabolic decompensation and severe organ failure dominates the clinical course. Despite the procedure, the outcome remains disappointing with no significant differences between MMA and PA.2 The diagnosis is based on the presence of these compounds in body fluids, which were identified by the examination of organic acid in the urine and the profile of acylcarnitine in the blood. The therapy is focused on high energy low-protein diet, carnitine supplementation, and metronidazole. Some patients with methylmalonic aciduria (MMA) respond to pharmacological doses of vitamin B12.3, 4 Due to the poor long-term prognosis, liver transplantation has recently been attempted to cure this underlying metabolic defect as a recent conventional treatment therapy. Neonatal onset PA is the most common clinical form of PA.5 In the first few days of life, infants with: lethargy, poor feeding, vomiting, untreated hypotonia may progress to encephalopathy and cardiorespiratory insufficiency. In children, signs can be apparent before NBS results are visible. Late Onset can raise a variety of concerns including developmental delay, intellectual disability, hypotonia, failure to thrive.6
Rare case presentation
A new-born boy at 11 days of life brought with complaints of breathing difficulty, abdominal distension, thrombocythemia, mild hypotonia, refusal to feed with fever for Two days. The baby was lethargic and dusky with Prolonged CRT (cardiac re synchronization Therapy) at the time of admission, with Heart rate 170 per minute, Respiratory rate 68 and oxygen saturation (SpO2) 97%, diffused O2 crying and with poor activity. Sub coastal retractions have seen in the Abdomen. Baby with pale appearance with pulse 148/min, lethargy with capillary blood glucose 50 mg/dl, with Spo2 99% saturation. Clinical Onset was at 11 days of life, with progressive life-threating Hypoxia ischemic encephalopathy with hyperammonaemia leads to failure to thrive, septicaemia with hyperbilirubinemia which relates to rule out Inborn errors of metabolism.
Maternal history
A mother with age of 30 years with 3° Consanguineous marriage. The baby was delivered to G5P2L2A1D0 mother with a history of pregnancy-induced hypertension, delivered via LSCS has cried at birth. Baby with a history of poor cry leads to birth asphyxia, A full-term baby with appropriate gestational age with gravida of five(G5). The mother’s first with age of Seven years Male child, the second one is an ectopic pregnancy, third was aborted at Four months and fourth was aborted at third months. The present is the fifth baby with a severe complications life-threatening.
Clinical investigations
The ultrasonography of the neonatal cranium was normal, abdomen with hepatomegaly, but the spleen was normal, Brain with cerebral edema. After the severe complications at 13 days of life, on both computed tomography and magnetic resonance imaging, IEM shows diffuse cerebral edema, Atrophic changes, and bilateral basal ganglia involvement. The ECG shows the ventricular septic defect with patent foramen ovale (PFO+).
Laboratory findings
The lab findings are notable with hyperammonemia with serum ammonia levels of 1065 umol/L, with CRP(C-reactive protein) is 36 mg/L, with Hb (Haemoglobin) 13.5 g/L, PCV 36 with total WBC 6300 x10 – 6µl, with platelets decreased when on admission 1.3 Lakhs, Blood urea nitrogen was increased 20 mg/DL, Serum Creatinine was 0.8 mg/DL, Serum calcium was 9 mg/dl, Serum sodium 136 mEq/L, Serum Potassium was 5.5 mEq/L. The Urine metabolic screening shows the urine ketones positive. To rule out Inborn errors of metabolism for new-born’s from capillary blood spots using gold-standard technology -Liquid chromatography Mass Spectrometry (LC-MS/MS) (Table 1). LCMS/MS Findings: The Interpretation shows the propinoylcarnitine (C3 – 43.5 µmol/L) was elevated. The ratio of the (c3/C2 – 247.27) which was found to be elevated, showed the positive screening for Propionic acidemia. GC – MS Findings: showed Elevated levels of 2- methyl citrate, 3-OH propionic acid.
Table 1
Results of the new-born screening using LC-MS/MS for amino acids and acyl carnitine profiling
Result & Discussion
Hyperammonaemia is an acute life-threatening condition which may cause severe neurological impairment and cerebral oedema.7, 8 Severe liver failure and the inherited metabolic diseases are the most common causes of hyperammonaemia in children. Ammonia, an NH3, is a major nitrogen source. Ammonia arises from protein breakdown, from the metabolism of amino acids, and is produced by the gut bacteria. Then ammonia is transported to periportal hepatocytes through portal circulation, where 90 percent of ammonia enters the urea cycle and is converted to urea. Because ammonia is not excreted (not water-soluble), (the remaining 10% is transmitted to derive hepatocytes where ammonia is converted to glutamine via glutamine synthetase (GS), a lower system of ability.9 Biochemical differences between the effects of chronic hyperammonaemia and the acutely increased concentration of ammonia point to a threshold effect of hyperammonaemia that may vary depending on the preceding levels of ammonia and the level of brain development. Unlike chronic hyperammonaemia, severe acute hyperammonaemia, on the other hand, leads to a decrease in ATP crisis situations with impaired consciousness due to acute hepatic encephalopathy or a decompensating inborn metabolism error, and a rapid rise in ammonia concentration.10 Elevated levels of ammonia are parallel levels of propionic acid, and are a good metabolic decompensation indicator. Ammonia can reach extremely high levels, approaching those found with urea cycle deficiencies in individuals. A secondary urea cycle defect in which propionic acid or its metabolites are hypothesized to inhibit N-acetyl glutamate synthetase or carbamoyl phosphate synthase I activity11, 12 is often attributed to the increased ammonia seen in PA. The urea cycle disorders indicate that the results are dictated not only by the level of hyperammonaemia but more importantly by the length of time the ammonia is elevated. So it is important that hyperammonaemia (and acidosis) be treated quickly and aggressively.13
