Alternative titles; symbols
SNOMEDCT: 124718009, 69080001; ICD10CM: E71.121; ORPHA: 35; DO: 14701;
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
Gene/Locus |
Gene/Locus MIM number |
|---|---|---|---|---|---|---|
| 3q22.3 | Propionicacidemia | 606054 | Autosomal recessive | 3 | PCCB | 232050 |
| 13q32.3 | Propionicacidemia | 606054 | Autosomal recessive | 3 | PCCA | 232000 |
A number sign (#) is used with this entry because propionic acidemia is caused by mutation in the genes encoding propionyl-CoA carboxylase, PCCA (232000) or PCCB (232050). Cells from patients with mutations in the PCCA gene fall into complementation group pccA. Cells from patients with mutations in the PCCB gene fall into complementation group pccBC. Mutations in the pccB subgroup occur in the N terminus of the PCCB gene, which includes the biotin-binding site, whereas mutations in the pccC subgroup occur in the C terminus of the PCCB gene (Fenton et al., 2001).
Propionic acidemia is an autosomal recessive metabolic disorder caused by defective functioning in the mitochondrial enzyme propionyl CoA carboxylase (PCC), resulting in the accumulation of propionic acid metabolites, and dysfunction in the respiratory chain and urea cycle pathways. The disorder is clinically heterogeneous. A neonatal-onset form is characterized by poor feeding, vomiting, and fatigue in the first days of life in a previously healthy infant, and if untreated, may be followed by lethargy, seizures, coma, and death. The neonatal form is frequently accompanied by metabolic acidosis with anion gap, ketonuria, hypoglycemia, hyperammonemia, and cytopenia. A late-onset form in older children and adults has a milder phenotype, is less common, and may present with developmental regression, chronic vomiting, protein intolerance, failure to thrive, hypotonia, and occasionally basal ganglia infarction, which may result in dystonia and choreoathetosis, and cardiomyopathy. Metabolically unstable individuals can have an acute decompensation that resembles the neonatal presentation, often precipitated by a catabolic stress such as infection, injury, or surgery, or an excessive intake of intact (i.e., complete, dietary, or natural) protein. Long-term manifestations of neonatal and late onset of propionic acidemia can include growth impairment, intellectual disability, seizures, basal ganglia lesions, pancreatitis, and cardiomyopathy. Other less common manifestations include optic atrophy, hearing loss, premature ovarian insufficiency, and chronic renal failure (summary by Jurecki et al., 2019).
The features of propionic acidemia are episodic vomiting, lethargy and ketosis, neutropenia, periodic thrombocytopenia, hypogammaglobulinemia, developmental retardation, and intolerance to protein. Outstanding chemical features are hyperglycinemia and hyperglycinuria. This disorder is not to be confused with hereditary glycinuria (138500), which is an autosomal dominant disorder.
Soriano et al. (1967) suggested that in the disorder first described by Childs et al. (1961), a generalized defect in utilization of amino acids results in excessive deamination of certain amino acids in muscle, with consequent hyperammonemia and ketoacidosis. In a second group of patients whose disorder is also termed hyperglycinemia, ketoacidosis, neutropenia, and thrombocytopenia have not been observed and glycine is the only amino acid present in excess in serum and urine; see glycine encephalopathy (605899).
Hsia et al. (1969) studied fibroblasts from a sister of the boy described by Childs et al. (1961) and demonstrated deficient propionate carboxylation as the basic defect in ketotic hyperglycinemia. Hsia et al. (1971) also showed that 'ketotic hyperglycinemia' is the same as propionic acidemia and is the result of a defect in PCC. In further studies on this patient, Brandt et al. (1974) demonstrated that with low protein diet, growth and intelligence developed normally to age 9 years; indeed, intelligence was superior. The family originally reported by Childs et al. (1961) had the pccA type of propionic acidemia (Wolf, 1986).
In a male Pakistani offspring of first-cousin parents, Gompertz et al. (1970) described acidosis and ketosis due to propionic acidemia, leading to death at 8 days of age. A sib had died at 2 weeks of age with metabolic acidosis and ketonuria. The defect was found to involve mitochondrial propionyl-CoA carboxylase. The same condition was described by Hommes et al. (1968).
Al Essa et al. (1998) pointed out that not only do acute intercurrent infections precipitate acidosis in propionic acidemia, but such infections are unusually frequent in propionic acidemia in Saudi Arabia. Propionic acidemia is unusually frequent in Saudi Arabia, with a frequency of 1 in 2,000 to 1 in 5,000, depending on the region. The disorder has a severe phenotype in Saudi Arabia. Al Essa et al. (1998) had information on approximately 90 patients; certain tribes accounted for almost 80% of these cases, suggesting a founder effect. The number of other cases of organic acidemias observed during the same period was 656. Longitudinal data, in some instances up to 8 years, were available for 38 patients with propionic acidemia. A high frequency of infections was observed in 80% of the patients. Most microorganisms implicated were unusual, suggesting an underlying immune deficiency. The infections occurred despite aggressive treatment with appropriate diets, carnitine, and, during acute episodes of the disease, with metronidazole, which suggested a global effect of the disease on T and B lymphocytes as well as on the bone marrow cells.
In a review of inherited metabolic disorders and stroke, Testai and Gorelick (2010) noted that patients with branched-chain organic aciduria, including isovaleric aciduria (243500), propionic aciduria, and methylmalonic aciduria (251000), can rarely have strokes. Cerebellar hemorrhage has been described in all 3 disorders, and basal ganglia ischemic stroke has been described in propionic aciduria and methylmalonic aciduria. These events may occur in the absence of metabolic decompensation.
Wenger et al. (2020) compared clinical and laboratory parameters between 16 individuals with propionic acidemia who were homozygous for an N536D mutation in the PCCB gene and 16 unaffected sibs. Affected individuals had a marginally but significantly elevated QTc compared to controls. Median ejection fraction and shortening fraction were significantly lower in patients. There was no difference in serum concentrations of creatine kinase-MB isoenzyme (see 123310), B-type natriuretic peptide (see 600295), or troponin I (see 191044) between patients and controls.
Kovacevic et al. (2022) evaluated echocardiogram parameters in a cross-sectional cohort of 18 patients with propionic acidemia, with an average age of 13.1 years. Left ventricular global longitudinal strain (LV-GLS) was abnormal in 72% of patients, whereas LV-fractional shortening and ejection fraction were only found to be reduced in 33.3% and 61% of patients, respectively. LV-myocardial performance index was found to be a reliable indicator of LV dysfunction in the setting of a dilated LV. Kovacevic et al. (2022) also observed a significant positive association between the median QTc interval and left ventricular diameter. The likelihood of having abnormal left ventricular functional measures increased with age. Kovacevic et al. (2022) concluded that measures such as LV-GLS may detect earlier or more subtle manifestations of LV dysfunction in propionic acidemia and have an impact on medical management.
Hillman et al. (1978) observed biotin-responsive propionic acidemia. Wolf and Hsia (1978) suggested that biotin-responsiveness can be tested by measuring propionyl-CoA carboxylase and beta-methylcrotonyl CoA carboxylase (see 609010 and 609014) in peripheral blood leukocytes before and after biotin. From kinetic analysis of complementations in heterokaryons of propionyl CoA carboxylase-deficient fibroblasts, Wolf et al. (1980) concluded that the 'bio' and 'pcc' mutations affect different genes; that complementation between pccA and pccB, pccC or pccBC lines is intergenic with subunit exchange and synthesis of new carboxylase molecules and that complementation between pccB and pccC mutants is interallelic. Wolf and Feldman (1982) considered it likely that the pccBC complementation group reflects mutations of the alpha subunit and the pccA group mutations of the beta subunit.
Using cDNA clones coding for the alpha and beta chains as probes, Lamhonwah and Gravel (1987) found absence of alpha mRNA in 4 of 6 pccA strains and the presence of beta mRNA in all pccA mutants studied. They also found the presence of both alpha and beta mRNAs in 3 pccBC, 2 pccB, and 3 pccC mutants. Ohura et al. (1989) presented evidence from which they concluded that beta-chain subunits of propionyl-CoA carboxylase are normally synthesized and imported into the mitochondria in excess of alpha-chain subunits, but only that portion assembled with alpha subunits escapes degradation. In pccA patients, the primary defect in alpha-chain synthesis leads secondarily to degradation of normally synthesized beta chains. The differential rates of synthesis of alpha and beta chains appear to account for the finding that persons heterozygous for pccBC mutations have normal carboxylase activity in their cells. Among 15 Japanese patients with propionic acidemia, Ohura et al. (1991) found that both the alpha and beta subunits were absent in 3 and low in 3 others; according to their previous data, they concluded that these 6 patients had an alpha-subunit defect. In 8 other patients, alpha subunits were normal, but the beta subunits were aberrant; these patients were considered to have beta-subunit defects. One of the 15 patients had apparently normal alpha and beta subunits. An altered MspI restriction pattern for PCCB cDNA, consisting of a unique 2.7-kb band, was found in 3 patients with beta-subunit deficiency.
Jurecki et al. (2019) stated that the incidence of propionic acidemia has been reported to be 1 in 100,000 newborns in Europe and 1:242,741 in the United States, but as high as 1:2,000 to 1:40,000 newborns in areas of the world with higher rates of consanguinity.
Prenatal Diagnosis
Buchanan et al. (1980) pointed out that propionic acidemia can be diagnosed either by an elevated quantity of the metabolite methylcitrate in amniotic fluid or by deficient activity of propionyl-CoA carboxylase in amniocytes. Contamination by maternal cells can give a normal value for the latter determination; methylcitrate assay may be the most reliable approach. Perez-Cerda et al. (1989) successfully diagnosed PCC deficiency in the first trimester of pregnancy by direct enzyme assay in uncultured chorionic villi.
Muro et al. (1999) reported prenatal diagnosis of an affected fetus based on DNA analysis in chorionic villus tissue in a family where the proband had previously been shown to carry the 1170insT mutation (232050.0004) and a private leu519-to-pro (L519P) mutation in the PCCB gene. Muro et al. (1999) also assessed carrier status in this family by DNA analysis.
The severe metabolic ketoacidosis in this disorder requires vigorous alkali therapy and protein restriction. Oral antibiotic therapy to reduce gut propionate production may also prove useful (Fenton et al., 2001).
Van Calcar et al. (1992) described a 22-year-old woman whose first episode of acute acidosis occurred at age 6 months following an upper respiratory infection; diagnosis of propionic acidemia was delayed until the age of 6.5 years. They gave detailed information on her pregnancy, which resulted in the birth of a healthy infant.
Jurecki et al. (2019) reported the outcome of a project to provide consensus recommendations for nutrition management of propionic acidemia based on literature reviews, surveys and expert input. Guidelines were provided for age-associated protein intake for well patients. Recommendations for nutrition management with the highest strength of evidence included regular nutrition assessments with monitoring of age-appropriate anthropometrics, the provision of intact protein rather than single L-amino acids to patients with low levels of plasma propiogenic amino acids, and development of an emergency home feeding and nutrition plan for patients with mild intercurrent illness. Other recommendations with a high strength of evidence included use of hormonal birth control in women who have metabolic instability during their menstrual cycle and establishment of good metabolic control prior to a conception. There was strong evidence that patients who have liver transplantation should receive protein at the daily recommended intake with increases beyond the daily recommended intake as tolerated, with lifetime biochemical and clinical monitoring.
Wenger et al. (2020) compared clinical and laboratory parameters in 16 individuals with propionic acidemia who were homozygous for an N536D mutation in the PCCB gene before and after suspension of therapy for 2 weeks. Medical foods, citrate, carnitine, coenzyme Q10, and biotin were suspended, and dietary protein was modestly restricted to between 1 and 1.5 g/kg/day. The authors found that suspension of therapy in these patients did not significantly alter branched chain amino acids, their alpha-ketoacid derivatives, urine ketones, or urine concentrations of most TCA cycle intermediates. There were no reliable correlations between therapeutic biomarkers (serum isoleucine, acetylcarnitine levels, TCA cycle intermediates), measures of PCC deficiency (plasma and urine methylcitrate, propionylcarnitine, glycine), and/or cardiac measures (ejection fraction, QTc interval). Carnitine supplementation significantly increased urine propionylcarnitine and its ratio to total carnitine. The patients remained clinically well during suspension of therapy. Wenger et al. (2020) concluded that treatment of individuals homozygous for the N536D mutation in the PCCB gene with protein restriction, prescription formula, and/or dietary supplements had limited effects on biomarkers of PCC deficiency. However, the data suggested that enteral carnitine supplementation is important for clearance of propionic acid, even though it may have a therapeutic effect.
Koeberl et al. (2024) treated 16 patients with propionic acidemia due to biallelic mutations in PCCA or PCCB with a lipid nanoparticle containing a PCCA or PCCB mRNA. This was a dose escalation study with an optional dose-optimized open-label extension. Two patients discontinued the study. Twelve patients completed the dose optimization phase and continued to the open label phase of the study, and 2 were still in the dose optimization phase at the time of the data report. The frequency of major decompensation events was reduced by 70% in the dose optimization phase compared to the 12-month pretreatment period. One patient experienced an episode of pancreatitis attributed to the treatment, and continued on the study at a reduced dose.
Ugarte et al. (1999) reviewed mutations in the PCCA and PCCB genes. A total of 24 PCCA mutations had been reported, mostly missense point mutations and a variety of splicing defects. No mutation was predominant in the Caucasian or Asian populations studied.
Among 10 patients with propionic acidemia, Desviat et al. (2006) identified 4 different PCCA splice site mutations and 3 different PCCB splice site mutations. The authors emphasized the different molecular effects of splicing mutations and the possible phenotypic consequences.
Zhao et al. (2022) developed a hypomorphic mouse model of propionic acidemia that had a complete knockout of the endogenous Pcca gene and heterozygosity for a human PCCA transgene with a hypomorphic A138T mutation. Starting at 3 weeks of age, the mutant mice had lower body weight and increased mortality compared to controls. Plasma C0- and C2-carnitine levels and the C3/C2 acylcarnitine levels were elevated in the mutant mice compared to controls. The mutant mice were studied during their basal state and if they displayed an acutely ill state. Blood ammonia levels and liver propionyl-CoA levels were elevated in the basal state and further elevated in the acutely ill state in the mutant mice compared to controls. Liver acetyl-CoA levels were lower in the basal state in the mutant mice and further lowered in the acutely ill state in the mutant mice compared to controls. Treatment of the mutant mice with carglumate resulted in lowered blood ammonia levels and improved growth.
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