High incidence of propionic acidemia in greenland is due to a prevalent mutation, 1540insCCC, in the gene for the beta-subunit of propionyl CoA carboxylase

Spectrum of Organic Aciduria Diseases in Tunisia: A 35-year Retrospective Study

Background

Organic aciduria diseases (OADs) occur worldwide, with differences in prevalence and patterns between populations.

Objectives

To describe the spectrum of OADs identified in Tunisia over a 35-years period.

Materials and Methods

This retrospective study included patients who were diagnosed with OADs between 1987 and 2022 in the Laboratory of Biochemistry, Rabta Hospital, Tunisia. Organic acids were analyzed using gas chromatography-mass spectrometry.

Results

A total of 30,670 urine samples were analyzed for OADs, of which 471 were positive for OADs. The estimated incidence of OADs in Tunisia was 6.78 per 100,000 live births. Methylmalonic (n = 146) and propionic (n = 90) acidurias were the most common OADs (estimated incidence: 2.10 and 1.30 per 100,000 live births, respectively). There were 54 cases of L-2-hydroxyglutatric acidurias and 30 cases of pyroglutamic acidurias, which makes it one of the highest in the world. The main clinical features were hypotonia (65%) and feeding difficulties (41%). Age at diagnosis was highly variable, ranging from 1 day to 49 years. Only 27% of the patients were diagnosed within the first month of life. The prevalence of OADs was highest in the Center-East and Southeast regions.

Conclusions

In Tunisia, OADs are relatively frequent, but there are shortcomings regarding the diagnosis of these disorders. The frequency and health/social impact of these disorders warrant the need for implementing newborn screening programs and suitable patient management.

Prevalence of propionic acidemia in China

Propionic acidemia (PA) is a rare autosomal recessive congenital disease caused by mutations in the PCCA or PCCB genes. Elevated propionylcarnitine, 2-methylcitric acid (2MCA), propionylglycine, glycine and 3-hydroxypropionate can be used to diagnose PA. Early-onset PA can lead to acute deterioration, metabolic acidosis, and hyperammonemia shortly after birth, which can result in high mortality and disability. Late-onset cases of PA have a more heterogeneous clinical spectra, including growth retardation, intellectual disability, seizures, basal ganglia lesions, pancreatitis, cardiomyopathy, arrhythmias, adaptive immune defects, rhabdomyolysis, optic atrophy, hearing loss, premature ovarian failure, and chronic kidney disease. Timely and accurate diagnosis and appropriate treatment are crucial to saving patients' lives and improving their prognosis. Recently, the number of reported PA cases in China has increased due to advanced diagnostic techniques and increased research attention. However, an overview of PA prevalence in China is lacking. Therefore, this review provides an overview of recent advances in the pathogenesis, diagnostic strategies, and treatment of PA, including epidemiological data on PA in China. The most frequent variants among Chinese PA patients are c.2002G > A in PCCA and c.1301C > T in PCCB, which are often associated with severe clinical symptoms. At present, liver transplantation from a living (heterozygous parental) donor is a better option for treating PA in China, especially for those exhibiting a severe metabolic phenotype and/or end-organ dysfunction. However, a comprehensive risk-benefit analysis should be conducted as an integral part of the decision-making process. This review will provide valuable information for the medical care of Chinese patients with PA.

Anesthetic Management of Children With Propionic Acidemia Undergoing Esophagogastroduodenoscopy

Propionic acidemia is a rare genetic disorder of metabolism that predisposes patients to metabolic acidosis, lethargy, neurologic dysfunction, developmental delays, and cardiomyopathy. Perioperative anesthetic management is guided toward mitigating the effects of preoperative fasting times, maintaining normovolemia, and preventing cardiovascular complications secondary to underlying cardiomyopathy. Commonly used anesthetic agents may have undesirable side effects in these patients. Propofol, the lactate in Lactated Ringer's, and neuromuscular blocking agents that undergo ester hydrolysis are poorly metabolized and can lead to metabolic acidosis. Opioids, such as fentanyl and morphine, should be used judiciously in patients with coexisting developmental delays to avoid oversedation and delayed time to resuming oral intake postanesthesia. In addition, inhaled anesthetics have direct myocardial depressive effects and can compromise cardiac function in the setting of pre-existing cardiomyopathy. The perioperative period represents a critical time in this population and appropriate planning is crucial to prevent perioperative morbidity. We present a case of an eight-year-old child undergoing esophagogastroduodenoscopy under general anesthesia and describe the anesthetic concerns we addressed to provide a safe perioperative course.

The presence of 3-hydroxypropionate and 1,3-propanediol suggests an alternative path for conversion of glycerol to Acetyl-CoA

BACKGROUND

In our recent study using [U-13C3]glycerol, a small subset of hamsters showed an unusual profile of glycerol metabolism: negligible gluconeogenesis from glycerol plus conversion of glycerol to 1,3-propanediol (1,3PDO) and 3-hydroxypropionate (3HP) which were detected in the liver and blood. The purpose of the current study is to evaluate the association of these unusual glycerol products with other biochemical processes in the liver.

METHODS

Fasted hamsters received acetaminophen (400 mg/kg; n = 16) or saline (n = 10) intraperitoneally. After waiting 2 h, all the animals received [U-13C3]glycerol intraperitoneally. Liver and blood were harvested 1 h after the glycerol injection for NMR analysis and gene expression assays.

RESULTS

1,3PDO and 3HP derived from [U-13C3]glycerol were detected in the liver and plasma of eight hamsters (two controls and six hamsters with acetaminophen treatment). Glycerol metabolism in the liver of these animals differed substantially from conventional metabolic pathways. [U-13C3]glycerol was metabolized to acetyl-CoA as evidenced with downstream products detected in glutamate and β-hydroxybutyrate, yet 13C labeling in pyruvate and glucose was minimal (p < 0.001, 13C labeling difference in each metabolite). Expression of aldehyde dehydrogenases was enhanced in hamster livers with 1,3PDO and 3HP (p < 0.05).

CONCLUSION

Detection of 1,3PDO and 3HP in the hamster liver was associated with unorthodox metabolism of glycerol characterized by conversion of 3HP to acetyl-CoA followed by ketogenesis and oxidative metabolism through the TCA cycle. Additional mechanistic studies are needed to determine the causes of unusual glycerol metabolism in a subset of these hamsters.

Lysine acetyltransferase 8 is involved in cerebral development and syndromic intellectual disability

Epigenetic integrity is critical for many eukaryotic cellular processes. An important question is how different epigenetic regulators control development and influence disease. Lysine acetyltransferase 8 (KAT8) is critical for acetylation of histone H4 at lysine 16 (H4K16), an evolutionarily conserved epigenetic mark. It is unclear what roles KAT8 plays in cerebral development and human disease. Here, we report that cerebrum-specific knockout mice displayed cerebral hypoplasia in the neocortex and hippocampus, along with improper neural stem and progenitor cell (NSPC) development. Mutant cerebrocortical neuroepithelia exhibited faulty proliferation, aberrant neurogenesis, massive apoptosis, and scant H4K16 propionylation. Mutant NSPCs formed poor neurospheres, and pharmacological KAT8 inhibition abolished neurosphere formation. Moreover, we describe KAT8 variants in 9 patients with intellectual disability, seizures, autism, dysmorphisms, and other anomalies. The variants altered chromobarrel and catalytic domains of KAT8, thereby impairing nucleosomal H4K16 acetylation. Valproate was effective for treating epilepsy in at least 2 of the individuals. This study uncovers a critical role of KAT8 in cerebral and NSPC development, identifies 9 individuals with KAT8 variants, and links deficient H4K16 acylation directly to intellectual disability, epilepsy, and other developmental anomalies.

A novel delins (c.773_819+47delinsAA) mutation of the PCCA gene associated with neonatal-onset propionic acidemia: a case report

Background

Propionic acidemia (PA)(OMIM#606054) is an inborn error of branched-chain amino acid metabolism, caused by defects in the propionyl-CoA carboxylase (PCC) enzyme which encoded by the PCCA and PCCB genes.

Case presentation

Here we report a Chinese neonate diagnosed with suspected PA based on the clinical symptoms, gas chromatography-mass spectrometry (GC/MS), and brain imaging tests. Targeted next-generation sequencing (NGS) was performed on the proband. We detected only one heterozygous recurrent nonsense variant (c.937C > T, p.Arg313Ter) in the PCCA gene. When we manually checked the binary alignment map (BAM) diagram of PCCA gene, we found a heterozygous deletion chr13:100915039-100915132delinsAA (c.773_819 + 47delinsAA) (GRCh37.p13) inside the exon 10 in the PCCA gene. The results were validated by Sanger sequencing and qPCR method in the family: the variant (c.937C > T, p.Arg313Ter) was in the maternal allele, and the delins was in the paternal allele. When the mother was pregnant again, prenatal diagnosis was carried out through amniocentesis at 18 weeks gestation, the fetus carried neither of the two mutations. After birth, newborn screening was undertaken, the result was negative.

Conclusions

We identified a recurrent c.937C > T and a novel c.773_819 + 47delinsAA mutations in the PCCA gene, which may be the genetic cause of the phenotype of this patient. Our findings expanded the spectrum of causative genotype-phenotype of the PCCA gene. For the cases, the NGS results revealed only a heterozygous mutation in autosomal recessive disease when the gene is associated with phenotypes, it is necessary to manually check the BAM diagram to improve the detection rate. Targeted NGS is an effective technique to detect the various genetic lesions responsible for the PA in one step. Genetic testing is essential for genetic counselling and prenatal diagnosis in the family to avoid birth defects.

Biochemical and anaplerotic applications of in vitro models of propionic acidemia and methylmalonic acidemia using patient-derived primary hepatocytes

Propionic acidemia (PA) and methylmalonic acidemia (MMA) are autosomal recessive disorders of propionyl-CoA (P-CoA) catabolism, which are caused by a deficiency in the enzyme propionyl-CoA carboxylase or the enzyme methylmalonyl-CoA (MM-CoA) mutase, respectively. The functional consequence of PA or MMA is the inability to catabolize P-CoA to MM-CoA or MM-CoA to succinyl-CoA, resulting in the accumulation of P-CoA and other metabolic intermediates, such as propionylcarnitine (C3), 3-hydroxypropionic acid, methylcitric acid (MCA), and methylmalonic acid (only in MMA). P-CoA and its metabolic intermediates, at high concentrations found in PA and MMA, inhibit enzymes in the first steps of the urea cycle as well as enzymes in the tricarboxylic acid (TCA) cycle, causing a reduction in mitochondrial energy production. We previously showed that metabolic defects of PA could be recapitulated using PA patient-derived primary hepatocytes in a novel organotypic system. Here, we sought to investigate whether treatment of normal human primary hepatocytes with propionate would recapitulate some of the biochemical features of PA and MMA in the same platform. We found that high levels of propionate resulted in high levels of intracellular P-CoA in normal hepatocytes. Analysis of TCA cycle intermediates by GC-MS/MS indicated that propionate may inhibit enzymes of the TCA cycle as shown in PA, but is also incorporated in the TCA cycle, which does not occur in PA. To better recapitulate the disease phenotype, we obtained hepatocytes derived from livers of PA and MMA patients. We characterized the PA and MMA donors by measuring key proximal biomarkers, including P-CoA, MM-CoA, as well as clinical biomarkers propionylcarnitine-to-acetylcarnitine ratios (C3/C2), MCA, and methylmalonic acid. Additionally, we used isotopically-labeled amino acids to investigate the contribution of relevant amino acids to production of P-CoA in models of metabolic stability or acute metabolic crisis. As observed clinically, we demonstrated that the isoleucine and valine catabolism pathways are the greatest sources of P-CoA in PA and MMA donor cells and that each donor showed differential sensitivity to isoleucine and valine. We also studied the effects of disodium citrate, an anaplerotic therapy, which resulted in a significant increase in the absolute concentration of TCA cycle intermediates, which is in agreement with the benefit observed clinically. Our human cell-based PA and MMA disease models can inform preclinical drug discovery and development where mouse models of these diseases are inaccurate, particularly in well-described species differences in branched-chain amino acid catabolism.

Deficient histone H3 propionylation by BRPF1-KAT6 complexes in neurodevelopmental disorders and cancer

Lysine acetyltransferase 6A (KAT6A) and its paralog KAT6B form stoichiometric complexes with bromodomain- and PHD finger-containing protein 1 (BRPF1) for acetylation of histone H3 at lysine 23 (H3K23). We report that these complexes also catalyze H3K23 propionylation in vitro and in vivo. Immunofluorescence microscopy and ATAC-See revealed the association of this modification with active chromatin. Brpf1 deletion obliterates the acylation in mouse embryos and fibroblasts. Moreover, we identify BRPF1 variants in 12 previously unidentified cases of syndromic intellectual disability and demonstrate that these cases and known BRPF1 variants impair H3K23 propionylation. Cardiac anomalies are present in a subset of the cases. H3K23 acylation is also impaired by cancer-derived somatic BRPF1 mutations. Valproate, vorinostat, propionate and butyrate promote H3K23 acylation. These results reveal the dual functionality of BRPF1-KAT6 complexes, shed light on mechanisms underlying related developmental disorders and various cancers, and suggest mutation-based therapy for medical conditions with deficient histone acylation.

Systematic literature review and meta-analysis on the epidemiology of propionic acidemia

Propionic acidemia (PA, OMIM #606054) is a serious, life-threatening, inherited, metabolic disorder caused by the deficiency of the mitochondrial enzyme propionyl-coenzyme A (CoA) carboxylase (EC 6.4.1.3). The primary objective of this study was to conduct a systematic literature review and meta-analysis on the epidemiology of PA. The literature search was performed covering Medline, Embase, Cochrane Database of Systematic Reviews, CRD Database, Academic Search Complete, CINAHL and PROSPERO databases. Websites of rare disease organizations were also searched for eligible studies. Of the 2338 identified records, 188 articles were assessed for eligibility in full text, 43 articles reported on disease epidemiology, and 31 studies were included into the quantitative synthesis. Due to the rarity of PA, broadly targeted population-based prevalence studies are not available. Nonetheless, implementation of newborn screening programs has allowed the estimation of the birth prevalence data of PA across multiple geographic regions. The pooled point estimates indicated detection rates of 0.29; 0.33; 0.33 and 4.24 in the Asia-Pacific, Europe, North America and the Middle East and North Africa (MENA) regions, respectively. Our systematic literature review and meta-analysis confirm that PA is an ultra-rare disorder, with similar detection rates across all regions with the exception of the MENA region where the disease, similar to other inherited metabolic disorders, is more frequent.

Organic acidurias in adults: late complications and management

Organic acidurias (synonym, organic acid disorders, OADs) are a heterogenous group of inherited metabolic diseases delineated with the implementation of gas chromatography/mass spectrometry in metabolic laboratories starting in the 1960s and 1970s. Biochemically, OADs are characterized by accumulation of mono-, di- and/or tricarboxylic acids ("organic acids") and corresponding coenzyme A, carnitine and/or glycine esters, some of which are considered toxic at high concentrations. Clinically, disease onset is variable, however, affected individuals may already present during the newborn period with life-threatening acute metabolic crises and acute multi-organ failure. Tandem mass spectrometry-based newborn screening programmes, in particular for isovaleric aciduria and glutaric aciduria type 1, have significantly reduced diagnostic delay. Dietary treatment with low protein intake or reduced intake of the precursor amino acid(s), carnitine supplementation, cofactor treatment (in responsive patients) and nonadsorbable antibiotics is commonly used for maintenance treatment. Emergency treatment options with high carbohydrate/glucose intake, pharmacological and extracorporeal detoxification of accumulating toxic metabolites for intensified therapy during threatening episodes exist. Diagnostic and therapeutic measures have improved survival and overall outcome in individuals with OADs. However, it has become increasingly evident that the manifestation of late disease complications cannot be reliably predicted and prevented. Conventional metabolic treatment often fails to prevent irreversible organ dysfunction with increasing age, even if patients are considered to be "metabolically stable". This has challenged our understanding of OADs and has elicited the discussion on optimized therapy, including (early) organ transplantation, and long-term care.

A Novel PCCA Mutation in a Patient With Late-Onset Propionic Acidemia Identified by Genetic Diagnosis Panel

Background: Propionic acidemia (PA) is an extremely rare autosomal recessive disorder which is caused by the deficiency of propionyl-CoA carboxylase (PCC) and associated with pathogenic variants in PCCA or PCCB gene. Case Report: Detection of PA in neonates is possible using Propionyl carnitine (C3) analysis by tandem mass spectrometry (MS/MS) in dried blood spots (DBS). Here we report one patient with PA. C3 in this case was normal in the initial screening and recall check and only manifested as the slightly increase of C3/C2, 3-hydroxypropionate in urine was only slightly elevated. Then two pathogenic mutations (c.802C>T/c.827delG) were detected in the PCCA gene by Genetic diagnosis panel. Among them, the variation rs774738181 (c.802C>T) was present on the dbSNP database which appeared to be "Likely pathogenic" in GenBank dbSNP (100915068). c.827delG was a novel frameshift mutation, leading to p.Gly276ValfsX46 mutation of amino acid sequence in PCCA. The patient underwent 1 year of follow-up, had total of 7 times and remain asymptomatic whose blood ammonia and liver function were normal. When the child was 1 year of age (in May of 2017), C3 and 3-Hydroxypropionate sudden elevated significantly, that proved pathogenicity of c.802C>T and c.827delG. Conclusion: Two novel mutations (c. 802C>T and c.827delG) in PCCA gene may be associated with late-onset PA, expanding its mutational spectrum. Maybe there is relation between the severity of propionyl-CoA carboxylase (PCC) activity defects and different genotypes.

Methylmalonic and propionic acidemias: clinical management update

PURPOSE OF REVIEW

Recent clinical studies and management guidelines for the treatment of the organic acidopathies methylmalonic acidemia (MMA) and propionic acidemia address the scope of interventions to maximize health and quality of life. Unfortunately, these disorders continue to cause significant morbidity and mortality due to acute and chronic systemic and end-organ injury.

RECENT FINDINGS

Dietary management with medical foods has been a mainstay of therapy for decades, yet well controlled patients can manifest growth, development, cardiac, ophthalmological, renal, and neurological complications. Patients with organic acidopathies suffer metabolic brain injury that targets specific regions of the basal ganglia in a distinctive pattern, and these injuries may occur even with optimal management during metabolic stress. Liver transplantation has improved quality of life and metabolic stability, yet transplantation in this population does not entirely prevent brain injury or the development of optic neuropathy and cardiac disease.

SUMMARY

Management guidelines should identify necessary screening for patients with methylmalonic acidemia and propionic acidemia, and improve anticipatory management of progressive end-organ disease. Liver transplantation improves overall metabolic control, but injury to nonregenerative tissues may not be mitigated. Continued use of medical foods in these patients requires prospective studies to demonstrate evidence of benefit in a controlled manner.

Recapitulation of metabolic defects in a model of propionic acidemia using patient-derived primary hepatocytes

BACKGROUND

Propionic acidemia (PA) is a disorder of intermediary metabolism with defects in the alpha or beta subunits of propionyl CoA carboxylase (PCCA and PCCB respectively) enzyme. We previously described a liver culture system that uses liver-derived hemodynamic blood flow and transport parameters to restore and maintain primary human hepatocyte biology and metabolism utilizing physiologically relevant milieu concentrations.

METHODS

In this study, primary hepatocytes isolated from the explanted liver of an 8-year-old PA patient were cultured in the liver system for 10 days and evaluated for retention of differentiated polarized morphology. The expression of PCCA and PCCB was assessed at a gene and protein level relative to healthy donor controls. Ammonia and urea levels were measured in the presence and absence of amino acid supplements to assess the metabolic consequences of branched-chain amino acid metabolism in this disease.

RESULTS

Primary hepatocytes from the PA patient maintained a differentiated polarized morphology (peripheral actin staining) over 10 days of culture in the system. We noted lower levels of PCCA and PCCB relative to normal healthy controls at the mRNA and protein level. Supplementation of branched-chain amino acids, isoleucine (5mM) and valine (5mM) in the medium, resulted in increased ammonia and decreased urea in the PA patient hepatocyte system, but no such response was seen in healthy hepatocytes or patient-derived fibroblasts.

CONCLUSIONS

We demonstrate for the first time the successful culture of PA patient-derived primary hepatocytes in a differentiated state, that stably retain the PCCA and PCCB enzyme defects at a gene and protein level. Phenotypic response of the system to an increased load of branched-chain amino acids, not possible with fibroblasts, underscores the utility of this system in the better understanding of the molecular pathophysiology of PA and examining the effectiveness of potential therapeutic agents in the most relevant tissue.

A novel PCCB mutation in a Thai patient with propionic acidemia identified by exome sequencing

Propionic acidemia (PA) is an inborn error of metabolism, caused by mutations in either the PCCA or PCCB gene, leading to mitochondrial accumulation of propionyl-CoA and its by-products. Here we report a 6-year-old Thai boy with PA who was born to consanguineous parents. Exome sequencing identified a novel homozygous frameshift insertion (c.379_380insA; p.T127NfsX160) in the PCCB gene, expanding its mutational spectrum.

Propionic acidemia in the Arab World

The autosomal recessive disease propionic acidemia (PA) is an inborn error of metabolism with highly variable clinical manifestations, caused by a deficiency of propionyl-CoA carboxylase (PCC) enzyme, due to mutations in either PCCA or PCCB genes, which encode the alpha and beta subunits of the PCC enzyme, respectively. The classical clinical presentation consists of poor feeding, vomiting, metabolic acidosis, hyperammonemia, lethargy, neurological problems, and developmental delay. PA seems to be a prevalent disease in the Arab World. Arab patients with PA seem to have the same classical clinical picture for PA with distinctive associated complications and other diseases. Most of the mutations found in Arab patients seem to be specific to the Arab population, and not observed in other ethnic groups. In this review, I will discuss in details the clinical and molecular profile of Arab patients with PA.

Proposed guidelines for the diagnosis and management of methylmalonic and propionic acidemia

Methylmalonic and propionic acidemia (MMA/PA) are inborn errors of metabolism characterized by accumulation of propionic acid and/or methylmalonic acid due to deficiency of methylmalonyl-CoA mutase (MUT) or propionyl-CoA carboxylase (PCC). MMA has an estimated incidence of ~ 1: 50,000 and PA of ~ 1:100’000 -150,000. Patients present either shortly after birth with acute deterioration, metabolic acidosis and hyperammonemia or later at any age with a more heterogeneous clinical picture, leading to early death or to severe neurological handicap in many survivors. Mental outcome tends to be worse in PA and late complications include chronic kidney disease almost exclusively in MMA and cardiomyopathy mainly in PA. Except for vitamin B₁₂ responsive forms of MMA the outcome remains poor despite the existence of apparently effective therapy with a low protein diet and carnitine. This may be related to under recognition and delayed diagnosis due to nonspecific clinical presentation and insufficient awareness of health care professionals because of disease rarity.

These guidelines aim to provide a trans-European consensus to guide practitioners, set standards of care and to help to raise awareness. To achieve these goals, the guidelines were developed using the SIGN methodology by having professionals on MMA/PA across twelve European countries and the U.S. gather all the existing evidence, score it according to the SIGN evidence level system and make a series of conclusive statements supported by an associated level of evidence. Although the degree of evidence rarely exceeds level C (evidence from non-analytical studies like case reports and series), the guideline should provide a firm and critical basis to guide practice on both acute and chronic presentations, and to address diagnosis, management, monitoring, outcomes, and psychosocial and ethical issues. Furthermore, these guidelines highlight gaps in knowledge that must be filled by future research. We consider that these guidelines will help to harmonize practice, set common standards and spread good practices, with a positive impact on the outcomes of MMA/PA patients.

Effects of adeno-associated virus serotype and tissue-specific expression on circulating biomarkers of propionic acidemia

Propionic acidemia (PA) is an autosomal recessive inborn error of metabolism caused by deficiency of propionyl-CoA carboxylase (PCC). This enzyme is composed of six PCCA and six PCCB subunits and mediates a critical step in catabolism of odd chain fatty acids and certain amino acids. Current treatment options for PA are limited to stringent dietary restriction of protein consumption and some patients undergo elective liver transplantation. We previously generated a hypomorphic model of PA, designated Pcca(-/-)(A138T), with 2% of wild-type enzyme activity that mimics many aspects of the human disease. In this study, we used the differing tissue tropisms of adeno-associated virus (AAV) to probe the ability of liver or muscle-directed gene therapy to treat systemic aspects of this disease that affects many cell types. Systemic therapy with muscle-biased AAV1, liver-biased AAV8, and broadly tropic AAVrh10 mediated significant biochemical corrections in circulating propionylcarnitine (C3) and methyl citrate by all vectors. The innate tissue bias of AAV1 and AAV8 gene expression was made more specific by the use of muscle-specific muscle creatine kinase (specifically MCK6) and hepatocyte-specific transthyretin (TTR) promoters, respectively. Under these targeted conditions, both vectors mediated significant long-term correction of circulating metabolites, demonstrating that correction of muscle and likely other tissue types in addition to liver is necessary to fully correct pathology caused by PA. Liver-specific AAV8-TTR-PCCA mediated better correction than AAV1-MCK-PCCA. These data suggest that targeted gene therapy may be a viable alternative to liver transplantation for PA. They also demonstrate the effects of tissue-specific and broad gene therapy on a cell autonomous systemic genetic disease.

Two frequent mutations associated with the classic form of propionic acidemia in Taiwan

Propionyl-CoA carboxylase (PCC) is involved in the catabolism of branched chain amino acids, odd-numbered fatty acids, cholesterol, and other metabolites. PCC consists of two subunits, α and β, encoded by the PCCA and PCCB genes, respectively. Mutations in the PCCA or PCCB subunit gene may lead to propionic acidemia. In this study, we performed mutation analysis on ten propionic acidemia patients from eight unrelated and nonconsanguineous families in Taiwan. Two PCCA mutations, c.229C→T (p.R77W) and c.1262A→C (p.Q421P), were identified in a PCCA-deficient patient. Six mutations in the PCCB gene, including c.-4156_183+3713del, c.580T→C (p.S194P), c.838dup (p.L280Pfs 11), c.1301C→T (p.A434V), c.1316A→G (P.Y439C), and c.1534C→T (p.R512C), were identified in seven PCCB-deficient families. The c.-4156_183+3713del mutation is the first known large deletion that affects the PCCB gene functions. Furthermore, the c.1301C→T and c.-4156_183+3713del mutations in the PCCB gene have not been reported previously. Clinical features demonstrated that these two frequent mutations are associated with low enzyme activity and a classic propionic acidemia phenotype.

Generation of a hypomorphic model of propionic acidemia amenable to gene therapy testing

Propionic acidemia (PA) is a recessive genetic disease that results in an inability to metabolize certain amino acids and odd-chain fatty acids. Current treatment involves restricting consumption of these substrates or liver transplantation. Deletion of the Pcca gene in mice mimics the most severe forms of the human disease. Pcca(-) mice die within 36 hours of birth, making it difficult to test intravenous systemic therapies in them. We generated an adult hypomorphic model of PA in Pcca(-) mice using a transgene bearing an A138T mutant of the human PCCA protein. Pcca(-/-)(A138T) mice have 2% of wild-type PCC activity, survive to adulthood, and have elevations in propionyl-carnitine, methylcitrate, glycine, alanine, lysine, ammonia, and markers associated with cardiomyopathy similar to those in patients with PA. This adult model allowed gene therapy testing by intravenous injection with adenovirus serotype 5 (Ad5) and adeno-associated virus 2/8 (AAV8) vectors. Ad5-mediated more rapid increases in PCCA protein and propionyl-CoA carboxylase (PCC) activity in the liver than AAV8 and both vectors reduced propionylcarnitine and methylcitrate levels. Phenotypic correction was transient with first generation Ad whereas AAV8-mediated long-lasting effects. These data suggest that this PA model may be a useful platform for optimizing systemic intravenous therapies for PA.

Case report: birth of healthy twins after preimplantation genetic diagnosis of propionic acidemia

PURPOSE

Development of an ad hoc protocol for the preimplantion genetic diagnosis of propionic acidemia in a couple carrying the mutations c.737G>T (G246V) and c.1218del14ins12 (ins/del) in the PCCB gene. Propionic acidemia is an autosomal recessive metabolic disorder where the body is unable to process certain parts of proteins and lipids. Symptoms manifest few days after birth and sometimes progress to more serious medical problems, including heart abnormalities, coma and death.

METHODS

Four short tandem repeat markers closely linked to the PCCB gene were tested, in order to support the direct mutation detection diagnosis. Multiplex fluorescent heminested polymerase chain reaction followed by fragment analysis and minisequencing was used.

RESULTS

Fourteen single blastomeres from nine embryos were tested and two carrier embryos were transferred, resulting in the birth of two healthy boys.

CONCLUSIONS

Preimplantation genetic diagnosis represents a valid reproductive option for couples affected of propionic acidemia, in order to avoid transmission to offspring.

Forty-three loci associated with plasma lipoprotein size, concentration, and cholesterol content in genome-wide analysis

While conventional LDL-C, HDL-C, and triglyceride measurements reflect aggregate properties of plasma lipoprotein fractions, NMR-based measurements more accurately reflect lipoprotein particle concentrations according to class (LDL, HDL, and VLDL) and particle size (small, medium, and large). The concentrations of these lipoprotein sub-fractions may be related to risk of cardiovascular disease and related metabolic disorders. We performed a genome-wide association study of 17 lipoprotein measures determined by NMR together with LDL-C, HDL-C, triglycerides, ApoA1, and ApoB in 17,296 women from the Women's Genome Health Study (WGHS). Among 36 loci with genome-wide significance (P<5×10⁻⁸) in primary and secondary analysis, ten (PCCB/STAG1 (3q22.3), GMPR/MYLIP (6p22.3), BTNL2 (6p21.32), KLF14 (7q32.2), 8p23.1, JMJD1C (10q21.3), SBF2 (11p15.4), 12q23.2, CCDC92/DNAH10/ZNF664 (12q24.31.B), and WIPI1 (17q24.2)) have not been reported in prior genome-wide association studies for plasma lipid concentration. Associations with mean lipoprotein particle size but not cholesterol content were found for LDL at four loci (7q11.23, LPL (8p21.3), 12q24.31.B, and LIPG (18q21.1)) and for HDL at one locus (GCKR (2p23.3)). In addition, genetic determinants of total IDL and total VLDL concentration were found at many loci, most strongly at LIPC (15q22.1) and APOC-APOE complex (19q13.32), respectively. Associations at seven more loci previously known for effects on conventional plasma lipid measures reveal additional genetic influences on lipoprotein profiles and bring the total number of loci to 43. Thus, genome-wide associations identified novel loci involved with lipoprotein metabolism—including loci that affect the NMR-based measures of concentration or size of LDL, HDL, and VLDL particles—all characteristics of lipoprotein profiles that may impact disease risk but are not available by conventional assay.

Genome-wide association studies (GWAS) of plasma lipoprotein fractions hold great promise for understanding lipid metabolism and its central role in cardiovascular disease and related disorders. Conventional assays for lipoprotein status determine total cholesterol content of low- or high-density lipoprotein particles (LDL-C or HDL-C, respectively) or total plasma triglyceride content (as an estimate of very-low density lipoprotein particle concentration [VLDL]). All three measures have been targets for recent GWAS. However, a more precise target for GWAS of lipoprotein metabolism would be the concentration of the individual lipoprotein particles according to class (LDL, HDL, VLDL) and size (small, medium, and large), all of which can be measured by NMR-based methods. In a population of 17,296 women of European ancestry from the Women's Genome Health Study, we have performed a GWAS for 22 lipoprotein measures derived from NMR-based and conventional assays. We find 43 genetic loci involved in lipoprotein metabolism, including 10 novel loci. The results offer a clearer picture of common genetic influences on lipoprotein metabolism than available previously, including genetic effects on the distribution of LDL, HDL, and VLDL particle size, as well as on IDL and VLDL particle concentration, neither of which can be assessed by conventional measures.

A high frequent BRCA1 founder mutation identified in the Greenlandic population

Approximately 10% of all breast and ovarian cancers are dominantly inherited and mutations are mainly found in the BRCA 1 and 2 genes. The penetrance of BRCA1 mutations is reported to be between 68 and 92% and confers a 36-92% life time risk of breast cancer. Most mutations in BRCA1 are uniquely occurring mutations, but founder mutations have been described. In this study we describe a founder mutation with wide spread presence in the Inuit population. We have screened 2,869 persons from Greenland for the presence of a BRCA1 mutation (p.Cys39Gly) only found in the Inuit population. The overall carrier frequency was 1.6% in the general population, but the frequency differs geographically from 0.6% on the West coast to 9.7% in the previously isolated population of the East coast. This is to our knowledge the highest population frequency of a BRCA1 mutation ever to be described. To determine the clinical relevance of the mutation, we have examined ten breast cancer patients and nine ovarian cancer patients from Greenland for the presence of the p.Cys39Gly mutation. We found three ovarian cancer patients (33%) and one breast cancer patient (10%) carrying the mutation. The high number of women carrying a BRCA1 mutation known to trigger the development of potentially lethal diseases leads us to recommend an offer of genetic counselling and test for the mutation to all females of Inuit origin, thereby hopefully preventing a number of breast and ovarian cancer deaths.

Organic acidemias: a methylmalonic and propionic focus

The management of children with organic acidemias (OAs) is limited in nursing literature. This article focuses on the two more common OAs, methylmalonic and propionic acidemias. Literature search was done on PUBMED, CINAHL, OVID, UptoDate, and GeneReview. The benefit of early diagnosis and treatment has been well documented, but many unresolved aspects of care management remain. Patient care is a complex necessitation and a lifelong follow-up for complications. Caring for patients with OA requires that nurses increase their familiarity with metabolic genetics and develop a better understanding of proper medical and nursing management while research continues to determine the most beneficial treatment and long-term care management methods.

Characterization of four variant forms of human propionyl-CoA carboxylase expressed in Escherichia coli

Propionyl-CoA carboxylase (PCC) is a biotin-dependent mitochondrial enzyme that catalyzes the conversion of propionyl-CoA to D-methylmalonyl-CoA. PCC consists of two heterologous subunits, alpha PCC and beta PCC, which are encoded by the nuclear PCCA and PCCB genes, respectively. Deficiency of PCC results in a metabolic disorder, propionic acidemia, which is sufficiently severe to cause neonatal death. We have purified three PCCs containing pathogenic mutations in the beta subunit (R165W, E168K, and R410W) and one PCCB polymorphism (A497V) to homogeneity to elucidate the potential structural and functional effects of these substitutions. We observed no significant difference in Km values for propionyl-CoA between wild-type and the variant enzymes, which indicated that these substitutions had no effect on the affinity of the enzyme for this substrate. Furthermore, the kinetic studies indicated that mutation R410W was not involved in propionyl-CoA binding in contrast to a previous report. The three mutant PCCs had half the catalytic efficiency of wild-type PCC as judged by the kcat/Km ratios. No significant differences have been observed in molecular mass or secondary structure among these enzymes. However, the variant PCCs were less thermostable than the wild-type. Following incubation at 47 degrees C, blue native-PAGE revealed a lower oligomeric form (alpha2beta2) in the three mutants not detectable in wild-type and the polymorphism. Interestingly, the lower oligomeric form was also observed in the corresponding crude Escherichia coli extracts. Our biochemical data and the structural analysis using a beta PCC homology model indicate that the pathogenic nature of these mutations is more likely to be due to a lack of assembly rather than disruption of catalysis. The strong favorable effect of the co-expressed chaperone proteins on PCC folding, assembly, and activity suggest that propionic acidemia may be amenable to chaperone therapy.

Towards a model to explain the intragenic complementation in the heteromultimeric protein propionyl-CoA carboxylase

Mutations in the PCCA or PCCB genes coding for alpha and beta subunits of propionyl CoA carboxylase can cause propionic acidemia. To understand the molecular basis of the intragenic complementation previously reported at the PCCB locus, we now examine the complementation behaviour of four carboxy-terminal and 11 amino-terminal naturally occurring mutant alleles both using cell fusion and reconstructing the complementation event by transfecting the mutant cDNAs to generate multimeric hybrid proteins. Alleles carrying mutations p.R410W and p.W531X are able to complement with 10 out of 11 amino-terminal mutations assayed. Only the unstable p.R512C, p.L519P and p.G112D mutants fail to complement. The results analyzed in the framework of the crystal structure of the homologous 12S transcarboxylase from Propionibacterium shermanii show that all mutant alleles studied are located at beta subunits interfaces, complementing alleles at the inter-trimer interface, where the catalysis probably happens, and non-complementing alleles at the intra-trimer interface, probably disrupting the trimer formation. Our results also show a remarkable stabilization effect when p.R410W is cotransfected with p.G246V. We propose a model for intragenic complementation requiring the production of two different beta subunits carrying carboxy and amino-terminal mutations that allow regenerating functional active sites and in which a stabilization effect between subunits could be relevant to ameliorate the biochemical phenotype of each mutation separately.

Propionic acidemia: mutation update and functional and structural effects of the variant alleles

Mutations in the PCCA or PCCB genes, encoding both subunits of propionyl-CoA carboxylase, result in propionic acidemia, a life-threatening inborn error of metabolism with autosomal recessive inheritance. To date, 41 mutations in the PCCA gene and 54 in the PCCB gene have been reported, most of them single base substitutions causing amino acid replacements, and a variety of small insertions and deletions and splicing defects. A greater heterogeneity is observed in the PCCA gene, specially in Caucasians, with no prevalent mutations, while in the Japanese population three mutations account for more than half of the alleles studied. For the PCCB gene a limited number of mutations is responsible for the majority of the alleles characterized in both Caucasian and Oriental populations. These two populations show a different mutational spectrum, only sharing some involving CpG dinucleotides probably as recurrent mutational events. Functional characterization of the mutant missense alleles has been accomplished using different prokaryotic and eukaryotic systems, and the structural consequences have been analyzed in the available crystal models. For the PCCA gene, the main molecular effect of the expressed mutations is related to protein instability, except two mutations in the active site predictably affecting ATP binding. In the PCCB gene the majority of the analyzed mutations are predicted to alter the active site conformation resulting in diminished activity. A few carboxy-terminal PCCB mutations affect the interaction between subunits and the assembly with PCCA to form a functional PCC oligomer. The amount of normal transcripts resulting from some PCCA and PCCB splicing mutations has also been analyzed. Overall, the data generated from the expression analysis reveal potential genotype-phenotype correlations for this clinically heterogeneous disorder.

Mutation spectrum of the PCCA and PCCB genes in Japanese patients with propionic acidemia

Propionic acidemia (PA) is an inborn error of organic acid metabolism caused by a deficiency of propionyl-CoA carboxylase. This enzyme is composed of two non-identical subunits, alpha and beta, which are encoded by the PCCA and PCCB genes, respectively. An enzyme deficiency can result from mutations in either PCCA or PCCB. To elucidate the mutation spectrum in Japanese patients, we have performed a mutation analysis of 30 patients with PA, which included nine previously reported patients. The study revealed that 15 patients were alpha-subunit deficient and 15 patients were beta-subunit deficient. Seven novel mutations were found (IVS18-6C >G, 1746G >A, C398R, G197E and IVS18+1G >A in the PCCA; A153P and IVS9+1G >T in the PCCB). Among these Japanese patients with alpha-subunit deficiencies, 923-924insT, IVS18-6C >G, and R399Q mutations were frequent and the total allelic frequency of these three mutations combined was 56% (17/30). This is in sharp contrast to the mutation spectrum found in Caucasian patients, where no prevalent mutations have been identified. Among the beta-subunit deficiencies, there were three frequent mutations; R410W, T428I, and A153P, whose allelic frequencies were 30, 26.7, and 13.3%, respectively. In conclusion, a limited number of mutations are predominant in both PCCA and PCCB genes among Japanese patients with propionic acidemia.

Functional analysis of PCCB mutations causing propionic acidemia based on expression studies in deficient human skin fibroblasts

Propionic acidemia (PA) is a recessive disorder caused by a deficiency of propionyl-CoA carboxylase (PCC), a dodecameric enzyme composed of two different proteins alpha-PCC and beta-PCC, nuclear encoded by the PCCA and PCCB genes, respectively. Mutations in either gene cause PA and to date, up to 47 different allelic variations in the PCCB gene have been identified in different populations. In this work, we describe the expression studies of 18 PCCB sequence changes in order to elucidate their functional consequences. We have used a PCCB-deficient transformed fibroblast cell line to target the wild-type and mutant proteins to their physiological situation, analysing the effect of the mutations on PCC activity and protein stability. Of the 18 mutant proteins tested for activity, those carrying the L17M and A497V substitutions showed an activity similar to the wild-type one, which proves that these changes do not have any effect on protein activity. The other 16 mutant proteins exhibited two different functional behaviours, 3 retained substantial activity (K218R, R410W and N536D), and the remaining 13 proteins showed null or very low activity. Western blot analysis demonstrated instability only for the L519P, R512C and G112D mutant proteins. We have proved the pathogenicity of R67S, R165Q and G112D mutation in PCCB gene, expressed for the first time in this work. The information derived from the expression analysis is discussed in the phenotype and genotype context in order to improve the knowledge of this complex disease.

Propionic acidemia: identification of twenty-four novel mutations in Europe and North America

Propionic acidemia is an inherited metabolic disease caused by the deficiency of the mitochondrial protein propionyl-CoA carboxylase (PCC), one of the four biotin-dependent enzymes. PCC is a multimeric protein composed of two different alpha- and beta-PCC subunits, nuclearly encoded by the PCCA and PCCB genes, respectively. Mutations in either gene cause the clinically heterogeneous disease propionic acidemia. In this work we describe the mutational analysis of PCCA and PCCB deficient patients from different European countries (Spain, Italy, Belgium, Croatia, and Austria) and from America (mainly USA). We report 24 novel PA mutations, nine affecting the PCCA gene and 15 affecting the PCCB gene. They include six missense mutations, one nonsense mutation, one point exonic mutation affecting splicing, seven splicing mutations affecting splice sequences, and nine short insertions or deletions, only two in-frame. We have found a highly heterogenous spectrum of PCCA mutations, most of the PCCA deficient patients are homozygous carrying a unique genotype. The PCCA mutational spectrum includes a high proportion of short insertions or deletions affecting one nucleotide. In the PCCA mutant alleles analyzed we have also found one single nucleotide change, a novel nonsynonymous SNP. On the other hand, the PCCB deficient patients carry a more reduced spectrum of mutations, 50% of them are missense. This work represents an extensive update of the mutational study of propionic acidemia providing important information about the worldwide distribution of PA mutations and representing another essential part in the study of the phenotype-genotype correlations for the prediction of the metabolic outcome and for the implementation of treatments tailored to each PA patient.

Functional characterization of PCCA mutations causing propionic acidemia

Propionic acidemia (PA, MIM 232000 and 232050) is caused by a deficiency of mitochondrial biotin-dependent propionyl-CoA carboxylase (PCC, EC 6.4.1.3), a heteropolymeric enzyme composed of alpha and beta subunits, which are encoded by the PCCA and PCCB genes, respectively. The PCCA protein (alpha subunit) is responsible for the formation of carboxybiotin upon hydrolysis of ATP and contains a C-terminal biotin-binding domain and a biotin carboxylase domain, defined by homology with other biotin-dependent carboxylases, some of them characterized structurally. More than 24 mutations have been found in the PCCA gene in patients with PA, among them 14 missense mutations and one in-frame deletion, for which the precise molecular effect is unknown. In this study, we have established the pathogenicity of 11 PCCA mutations (10 missense and an in-frame deletion) by expression studies in deficient fibroblasts and in a cell-free in vitro system, and analyzed the effect of each mutation on PCC activity, protein stability and domain structure. The results show that most mutant proteins show an increased turnover and are functionally deficient, suggesting that the structural alterations they cause are incompatible with normal assembly to produce a stable, functional PCC oligomer. These results are discussed in the context of the genotype-phenotype correlations in PCCA-deficient PA patients.

Propionic acidemia: analysis of mutant propionyl-CoA carboxylase enzymes expressed in Escherichia coli

Deficiency of propionyl-CoA carboxylase (PCC) results in propionic acidemia, an autosomal recessive disorder characterized by ketoacidosis sufficiently severe to cause neonatal death. PCC is involved in the catabolism of branched-chain amino acids, odd-chain fatty acids, and cholesterol. The enzyme is a biotin-dependent mitochondrial protein composed of two heterologous subunits arranged into an 800-kDa alpha(6 )beta(6) dodecameric structure. Approximately 60 mutations have been reported in the nuclear genes PCCA and PCCB that encode the two PCC subunits. The vast majority of these mutations have not been examined at the protein level. We present an initial characterization of 13 mutations located in exons 1, 3-7, and 12-14 of PCCB. After expression in E. coli, these recombinant mutant enzymes were analyzed for stability, biotinylation, alpha-beta subunit interaction, and activity. Our results show a functional dichotomy in these PCCB mutations with some mutants (R44P, S106R, G131R, G198D, V205D, I408del, and M442T) capable of varying degrees of assembly but forming catalytically inactive PCC proteins. Other PCCB mutants (R165W, E168K, D178H, P228L, and R410W) that are PCC deficient in patient-derived fibroblasts, were found to be capable of expressing wild-type level PCC activity when assembled in our chaperone-assisted E. coli expression system. This result indicates that these mutations exert their pathogenic effect due to an inability to assemble correctly in patients' cells. This initial screen has identified a range of mutant PCC proteins that are sufficiently stable to be purified and subsequently used for structure-function analysis to further elucidate the complex relationship between genotype and phenotype in propionic acidemia.

cDNA cloning, mapping and expression of the mouse propionyl CoA carboxylase beta (pccb), the gene for human type II propionic acidaemia

Propionyl CoA carboxylase (PCC) is a mitochondrial, biotin-dependent enzyme involved in the catabolism of amino acids, odd-chained fatty acids and other metabolites. PCC is composed of two equal subunits, alpha and beta, which are encoded by two separate genes at two distinct human loci. Mutations of either gene in humans results in propionic acidemia (PA). To identify the mouse cDNA for the propionyl CoA carboxylase beta-subunit (pccb), we have screened the mouse EST database using the human sequence. The murine mRNA transcript is approximately 2.3 kb, nearly 500 bps larger than the human approximately 1.8 kb transcript. A PAC genomic DNA clone from the mouse was also isolated and used to generate probes and PCR primers for mapping the pccb locus in the mouse. Both the C57Bl/6JEi and Spret/Ei alleles for regions flanking the pccb gene were sequenced to identify RFLPs. The Jackson Laboratory BSS and BSB backcross panel DNAs were then analyzed using a DdeI polymorphism placing the pccb locus on mouse chromosome 9. Northern blots of adult tissue show that the pccb gene is broadly expressed in the mouse. The approximately 2.3 kb transcript is most abundantly expressed in the kidney, liver, small intestine and stomach tissues.

Changes in the carboxyl terminus of the beta subunit of human propionyl-CoA carboxylase affect the oligomer assembly and catalysis: expression and characterization of seven patient-derived mutant forms of PCC in Escherichia coli

Propionyl-CoA carboxylase (PCC) catalyzes the biotin-dependent carboxylation of propionyl-CoA to d-methylmalonyl-CoA in the mitochondrial matrix. Human PCC is a dodecamer composed of pairs of nonidentical alpha and beta subunits encoded by PCCA and PCCB genes, respectively. Deficiency of PCC results in propionic acidemia (PA), a metabolic disorder characterized by severe metabolic ketoacidosis, vomiting, lethargy, and hypotonia. To date, almost 60 mutations have been reported in both genes. Exon 15 of the beta subunit is one of the two sites where a number of mutations have been identified in PA patients. In the primary betaPCC sequence, these mutations lead to three substitutions (R512C, L519P, and N536D), three truncations (R499X, R514X, and W531X), and one insertion (A51_R514insP). We expressed these mutant proteins in Escherichia coli in which the GroESL complex was overexpressed. The only mutation that does not impact the stability of mutant betaPCC in bacteria is W531X. The remaining mutations lead to either complete (L519P, N536D) or partial (R499X, R512C, A513_R514insP, and R514X) degradation of the mutant subunits. Size-exclusion chromatography revealed that R512C and W531X do not affect the assembly of alphaPCC and betaPCC to active oligomers. Specific activities for these mutant proteins, however, were only 3.9 and 10% of the wild type, respectively. Taken together, the carboxyl-terminal portion of 40 amino acid residues of the beta subunit affects the stability and the assembly of the alpha and beta subunits as well as the carboxylation of propionyl-CoA.