Intellectual disability and autism in propionic acidemia: a biomarker-behavioral investigation implicating dysregulated mitochondrial biology.

Propionic acidemia (PA) is an autosomal recessive condition (OMIM #606054), wherein pathogenic variants in PCCA and PCCB impair the activity of propionyl-CoA carboxylase. PA is associated with neurodevelopmental disorders, including intellectual disability (ID) and autism spectrum disorder (ASD); however, the correlates and mechanisms of these outcomes remain unknown. Using data from a subset of participants with PA enrolled in a dedicated natural history study (n = 33), we explored associations between neurodevelopmental phenotypes and laboratory parameters. Twenty (61%) participants received an ID diagnosis, and 12 of the 31 (39%) who were fully evaluated received the diagnosis of ASD. A diagnosis of ID, lower full-scale IQ (sample mean = 65 ± 26), and lower adaptive behavior composite scores (sample mean = 67 ± 23) were associated with several biomarkers. Higher concentrations of plasma propionylcarnitine, plasma total 2-methylcitrate, serum erythropoietin, and mitochondrial biomarkers plasma FGF21 and GDF15 were associated with a more severe ID profile. Reduced 1-13C-propionate oxidative capacity and decreased levels of plasma and urinary glutamine were also associated with a more severe ID profile. Only two parameters, increased serum erythropoietin and decreased plasma glutamine, were associated with ASD. Plasma glycine, one of the defining features of PA, was not meaningfully associated with either ID or ASD. Thus, while both ID and ASD were commonly observed in our PA cohort, only ID was robustly associated with metabolic parameters. Our results suggest that disease severity and associated mitochondrial dysfunction may play a role in CNS complications of PA and identify potential biomarkers and candidate surrogate endpoints.

Identification and characterization of the largest deletion in the PCCA gene causing severe acute early-onset form of propionic acidemia.

Whole-exome sequencing (WES) is an excellent method for the diagnosis of diseases of uncertain or heterogeneous genetic origin. However, it has limitations for detecting structural variations such as InDels, which the bioinformatics analyzers must be aware of. This study aimed at using WES to evaluate the genetic cause of the metabolic crisis in a 3-day-old neonate admitted to the neonatal intensive care unit (NICU) and deceased after a few days. Tandem mass spectrometry (MS/MS) showed a significant increase in propionyl carnitine (C3), proposing methylmalonic acidemia (MMA) or propionic acidemia (PA). WES demonstrated a homozygous missense variant in exon 4 of the BTD gene (NM_000060.4(BTD):c.1330G > C), responsible for partial biotinidase deficiency. Segregation analysis of the BTD variant revealed the homozygous status of the asymptomatic mother. Furthermore, observation of the bam file, around genes responsible for PA or MMA, by Integrative Genomics Viewer (IGV) software displayed a homozygous large deletion in the PCCA gene. Comprehensive confirmatory studies identified and segregated a novel outframe deletion of 217,877 bp length, "NG_008768.1:g.185211_403087delinsTA", extended from intron 11 to 21 of the PCCA, inducing a premature termination codon and activation of nonsense-mediated mRNA decay (NMD). Homology modeling of the mutant PCCA demonstrated eliminating the protein's active site and critical functional domains. Thereupon, this novel variant is suggested as the largest deletion in the PCCA gene, causing an acute early-onset PA. These results could expand the PCCA variants spectrum, and improve the existing knowledge on the molecular basis of PA, as well as provide new evidence of pathogenicity of the variant (NM_000060.4(BTD):c.1330G > C.

A common benign intronic deletion masking a pathogenic deep intronic PCCB variant - genome sequencing and RNA studies to the rescue.

Propionic acidemia (PA) is an autosomal recessive metabolic disorder caused by variants in PCCA or PCCB, both sub-units of the propionyl-CoA carboxylase (PCC) enzyme. PCC is required for the catabolism of certain amino acids and odd-chain fatty acids. In its absence, the accumulated toxic metabolites cause metabolic acidosis, neurologic symptoms, multi-organ dysfunction and possible death. The clinical presentation of PA is highly variable, with typical onset in the neonatal or early infantile period. We encountered two families, whose children were diagnosed with PA. Exome sequencing (ES) failed to identify a pathogenic variant, and we proceeded with genome sequencing (GS), demonstrating homozygosity to a deep intronic PCCB variant. RNA analysis established that this variant creates a pseudoexon with a premature stop codon. The parents are variant carriers, though three of them display pseudo-homozygosity due to a common large benign intronic deletion on the second allele. The parental presumed homozygosity merits special attention, as it masked the causative variant at first, which was resolved only by RNA studies. Arriving at a rapid diagnosis, whether biochemical or genetic, can be crucial in directing lifesaving care, concluding the diagnostic odyssey, and allowing the family prenatal testing in subsequent pregnancies. This study demonstrates the power of integrative genetic studies in reaching a diagnosis, utilizing GS and RNA analysis to overcome ES limitations and define pathogenicity. Importantly, it highlights that intronic deletions should be taken into consideration when analyzing genomic data, so that pseudo-homozygosity would not be misinterpreted as true homozygosity, and pathogenic variants will not be mislabeled as benign.

Relief of CoA sequestration and restoration of mitochondrial function in a mouse model of propionic acidemia.

Propionic acidemia (PA, OMIM 606054) is a devastating inborn error of metabolism arising from mutations that reduce the activity of the mitochondrial enzyme propionyl-CoA carboxylase (PCC). The defects in PCC reduce the concentrations of nonesterified coenzyme A (CoASH), thus compromising mitochondrial function and disrupting intermediary metabolism. Here, we use a hypomorphic PA mouse model to test the effectiveness of BBP-671 in correcting the metabolic imbalances in PA. BBP-671 is a high-affinity allosteric pantothenate kinase activator that counteracts feedback inhibition of the enzyme to increase the intracellular concentration of CoA. Liver CoASH and acetyl-CoA are depressed in PA mice and BBP-671 treatment normalizes the cellular concentrations of these two key cofactors. Hepatic propionyl-CoA is also reduced by BBP-671 leading to an improved intracellular C3:C2-CoA ratio. Elevated plasma C3:C2-carnitine ratio and methylcitrate, hallmark biomarkers of PA, are significantly reduced by BBP-671. The large elevations of malate and α-ketoglutarate in the urine of PA mice are biomarkers for compromised tricarboxylic acid cycle activity and BBP-671 therapy reduces the amounts of both metabolites. Furthermore, the low survival of PA mice is restored to normal by BBP-671. These data show that BBP-671 relieves CoA sequestration, improves mitochondrial function, reduces plasma PA biomarkers, and extends the lifespan of PA mice, providing the preclinical foundation for the therapeutic potential of BBP-671.

Neuropathological report of propionic acidemia.

Propionic acidemia (PA) is an autosomal recessive inheritable metabolic disease caused by mutations in the propionyl CoA carboxylase gene (PCC) that affects multiple systems of the human body. Here, we report neuropathological findings of a PA patient. The patient was a male infant who presented with increasing lethargy and poor feeding from four days postpartum. He gradually became comatose and died from complications after liver transplantation at three months old. The results of laboratory examination were consistent with PA, and genetic analysis revealed compound heterozygous mutations in the gene for PCC subunit beta: c.838dupC (rs769968548) and c.1127G>T (rs142982097). Brain-restricted autopsy was performed 23 h after his death, and the neuropathological examination revealed distinct astrocytosis, oligodendrocytic loss, neuronal loss, and demyelination across the brainstem, motor cortex, basal ganglia, and thalamus. Spongiosis, vacuolization, and the appearance of Alzheimer type II astrocytes and activated microglia were observed as well. This is the first brain autopsy report of PA with a clear genetic cause.

Propionic acidemia in mice: Liver acyl-CoA levels and clinical course.

Propionic acidemia (PA) is a severe autosomal recessive metabolic disease caused by deficiency of propionyl-CoA carboxylase (PCC). We studied PA transgenic (Pat) mice that lack endogenous PCC but express a hypoactive human PCCA cDNA, permitting their survival. Pat cohorts followed from 3 to 20 weeks of age showed growth failure and lethal crises of lethargy and hyperammonemia, commoner in males (27/50, 54%) than in females (11/52, 21%) and occurring mainly in Pat mice with the most severe growth deficiency. Groups of Pat mice were studied under basal conditions (P-Ba mice) and during acute crises (P-Ac). Plasma acylcarnitines in P-Ba mice, compared to controls, showed markedly elevated C3- and low C2-carnitine, with a further decrease in C2-carnitine in P-Ac mice. These clinical and biochemical findings resemble those of human PA patients. Liver acyl-CoA measurements showed that propionyl-CoA was a minor species in controls (propionyl-CoA/acetyl-CoA ratio, 0.09). In contrast, in P-Ba liver the ratio was 1.4 and in P-Ac liver, 13, with concurrent reductions of the levels of acetyl-CoA and other acyl-CoAs. Plasma ammonia levels in control, P-Ba and P-Ac mice were 109 ± 10, 311 ± 48 and 551 ± 61 µmol/L respectively. Four-week administration to Pat mice, of carglumate (N-carbamyl-L-glutamic acid), an analogue of N-carbamylglutamate, the product of the only acyl-CoA-requiring reaction directly related to the urea cycle, was associated with increased food consumption, improved growth and absence of fatal crises. Pat mice showed many similarities to human PA patients and provide a useful model for studying tissue pathophysiology and treatment outcomes.

[Phenotypes and genotypes of 78 patients with propionic acidemia].

Objective: Propionic acidemia is a rare inherited metabolic disorder caused by propionyl CoA carboxylase (PCC) deficiency. This study aims to analyze the clinical characteristics and gene variations of Chinese patients with propionic acidemia, and to explore the correlation between clinical phenotypes and genotypes. Methods: Single-center, retrospective and observational study. Seventy-eight patients of propionic acidemia (46 males and 32 females) from 20 provinces and autonomous regions were admitted from January 2007 to April 2022. Their age of initial diagnosis ranged from 7 days to 15 years. The clinical manifestations, biochemical and metabolic abnormalities, genetic variations, diagnosis, treatment and outcome were studied. Chi-Square test or Mann-Whitney U test were used for statistical analysis. Results: Among 78 cases, 6 (7.7%) were identified by newborn screening; 72 (92.3%) were clinically diagnosed after onset, and the age of onset was 2 hours after birth to 15 years old; 32 cases had early-onset disease and 40 cases had late-onset disease. The initial manifestations included lethargy, hypotonia, vomiting, feeding difficulties, developmental delay, epilepsy, and coma. Among the 74 cases who accepted gene analysis, 35 (47.3%) had PCCA variants and 39 (52.7%) had PCCB variants. A total of 39 PCCA variants and 32 PCCB variants were detected, among which c.2002G>A and c.229C>T in PCCA and c.838dupC and c.1087T>C in PCCB were the most common variants in this cohort. The variants c.1228C>T and c.1283C>T in PCCB may be related to early-onset type. The variants c.838dupC, c.1127G>T and c.1316A>G in PCCB, and c.2002G>A in PCCA may be related to late-onset disease. Six patients detected by newborn screening and treated at asymptomatic stage developed normal. The clinically diagnosed 72 cases had varied complications. 10 (12.8%) cases of them died. 62 patients improved after metabolic therapy by L-carnitine and diet. Six patients received liver transplantation because of recurrent metabolic crisis. Their clinical symptoms were markedly improved. Conclusion: The clinical manifestations of propionic acidemia are complex and lack of specificity. Newborn screening and high-risk screening are keys for early treatment and better outcome. The correlation between the genotype and phenotype of propionic acidemia is unclear, but certain variants may be associated with early-onset or late-onset propionic acidemia.

Fatal metabolic stroke in a child with propionic acidemia 11 years post liver transplant.

Propionic acidemia is a rare autosomal recessive inborn error of metabolism caused by a deficiency of propionyl CoA carboxylase which often manifests with frequent metabolic decompensations and risk of neurological injury. Outcomes with medical therapy remain suboptimal. Liver transplantation has been shown to be a therapeutic option for patients and results in a milder phenotype of the disease and partial correction of the enzyme defect. Liver transplantation has been increasingly reported over the last decade and experience in managing these patients is improving. Long-term outcomes are generally good; however, the risk of complications still exists despite transplantation. We report a child who presented with a fatal metabolic stroke 11 years post liver transplant without any biochemical evidence of decompensation. We highlight the need to closely monitor these patients lifelong despite liver transplantation and maintain multidisciplinary working between hepatology and metabolic clinicians.

Metabolic perturbations mediated by propionyl-CoA accumulation in organs of mouse model of propionic acidemia.

Propionic acidemia (PA) is an autosomal recessive metabolic disorder after gene encoding propionyl-CoA carboxylase, Pcca or Pccb, is mutated. This genetic disorder could develop various complications which are ascribed to dysregulated propionyl-CoA metabolism in organs. However, the effect of attenuated PCC on propionyl-CoA metabolism in different organs remains to be fully understood. We investigated metabolic perturbations in organs of Pcca-/-(A138T) mice (a mouse model of PA) under chow diet and acute administration of [13C3]propionate to gain insight into pathological mechanisms of PA. With chow diet, the metabolic alteration is organ dependent. l-Carnitine reduction induced by propionylcarnitine accumulation only occurs in lung and liver of Pcca-/- (A138T) mice. [13C3]Propionate tracing data demonstrated that PCC activity was dramatically reduced in Pcca-/-(A138T) brain, lung, liver, kidney, and adipose tissues, but not significantly changed in Pcca-/-(A138T) muscles (heart and skeletal muscles) and pancreas, which was largely supported by PCCA expression data. The largest expansion of propionylcarnitine in Pcca-/-(A138T) heart after acute administration of propionate indicated the vulnerability of heart to high circulating propionate. The overwhelming propionate in blood also stimulated ketone production from the increased fatty acid oxidation in Pcca-/-(A138T) liver by lowering malonyl-CoA, which has been observed in cases where metabolic decompensation occurs in PA patients. This work shed light on organ-specific metabolic alternations under varying severities of PA.

A novel small molecule approach for the treatment of propionic and methylmalonic acidemias.

Propionic Acidemia (PA) and Methylmalonic Acidemia (MMA) are inborn errors of metabolism affecting the catabolism of valine, isoleucine, methionine, threonine and odd-chain fatty acids. These are multi-organ disorders caused by the enzymatic deficiency of propionyl-CoA carboxylase (PCC) or methylmalonyl-CoA mutase (MUT), resulting in the accumulation of propionyl-coenzyme A (P-CoA) and methylmalonyl-CoA (M-CoA in MMA only). Primary metabolites of these CoA esters include 2-methylcitric acid (MCA), propionyl-carnitine (C3), and 3-hydroxypropionic acid, which are detectable in both PA and MMA, and methylmalonic acid, which is detectable in MMA patients only (Chapman et al., 2012). We deployed liver cell-based models that utilized PA and MMA patient-derived primary hepatocytes to validate a small molecule therapy for PA and MMA patients. The small molecule, HST5040, resulted in a dose-dependent reduction in the levels of P-CoA, M-CoA (in MMA) and the disease-relevant biomarkers C3, MCA, and methylmalonic acid (in MMA). A putative working model of how HST5040 reduces the P-CoA and its derived metabolites involves the conversion of HST5040 to HST5040-CoA driving the redistribution of free and conjugated CoA pools, resulting in the differential reduction of the aberrantly high P-CoA and M-CoA. The reduction of P-CoA and M-CoA, either by slowing production (due to increased demands on the free CoA (CoASH) pool) or enhancing clearance (to replenish the CoASH pool), results in a net decrease in the CoA-derived metabolites (C3, MCA and MMA (MMA only)). A Phase 2 study in PA and MMA patients will be initiated in the United States.

Increased protein propionylation contributes to mitochondrial dysfunction in liver cells and fibroblasts, but not in myotubes.

Post-translational protein modifications derived from metabolic intermediates, such as acyl-CoAs, have been shown to regulate mitochondrial function. Patients with a genetic defect in the propionyl-CoA carboxylase (PCC) gene clinically present symptoms related to mitochondrial disorders and are characterised by decreased mitochondrial respiration. Since propionyl-CoA accumulates in PCC deficient patients and protein propionylation can be driven by the level of propionyl-CoA, we hypothesised that protein propionylation could play a role in the pathology of the disease. Indeed, we identified increased protein propionylation due to pathologic propionyl-CoA accumulation in patient-derived fibroblasts and this was accompanied by defective mitochondrial respiration, as was shown by a decrease in complex I-driven respiration. To mimic pathological protein propionylation levels, we exposed cultured fibroblasts, Fao liver cells and C2C12 muscle myotubes to propionate levels that are typically found in these patients. This induced a global increase in protein propionylation and histone protein propionylation and was also accompanied by a decrease in mitochondrial respiration in liver and fibroblasts. However, in C2C12 myotubes propionate exposure did not decrease mitochondrial respiration, possibly due to differences in propionyl-CoA metabolism as compared to the liver. Therefore, protein propionylation could contribute to the pathology in these patients, especially in the liver, and could therefore be an interesting target to pursue in the treatment of this metabolic disease.

Mitochondrial damage in renal epithelial cells is potentiated by protein exposure in propionic aciduria.

Propionic aciduria (PA) is caused by deficiency of the mitochondrial enzyme propionyl-CoA carboxylase (PCC). Due to inefficient propionate catabolism patients are endangered by life-threatening ketoacidotic crisis. Protein and amino acid restriction are major therapeutic pillars. However, long-term complications like neurological deterioration and cardiac abnormalities cannot be prevented. Chronic kidney disease (CKD), which is a well-known characteristic of methylmalonic aciduria two enzymatic steps downstream from PCC, has been recognized as a novel late-onset complication in PA. The pathophysiology of CKD in PA is unclear. We investigated mitochondrial structure and metabolism in human renal tubular cells of healthy controls and PA patients. The cells were exposed to either standard cell culture conditions (NT), high protein (HP) or high concentrations of isoleucine and valine (I/V). Mitochondrial morphology changed to condensed, fractured morphology in PA cells irrespective of the cell culture medium. HP and I/V exposure, however, potentiated oxidative stress in PA cells. Mitochondrial mass was enriched in PA cells, and further increased by HP and I/V exposure suggesting a need for compensation. Alterations in the tricarboxylic acid cycle intermediates and accumulation of medium- and long-chain acylcarnitines pointed to altered mitochondrial energy metabolism. Mitophagy was silenced while autophagy as cellular defense mechanisms was highly active in PA cells. The data demonstrate that PA is associated with renal mitochondrial damage which is aggravated by protein and I/V load. Preservation of mitochondrial energy homeostasis in renal cells may be a potential future therapeutic target.

Characterization and directed evolution of propionyl-CoA carboxylase and its application in succinate biosynthetic pathway with two CO2 fixation reactions.

Propionyl-CoA carboxylase (PCC) is a promising enzyme in the fields of biological CO2 utilization, synthesis of natrual products, and so on. The activity and substrate specificity of PCC are dependent on its key subunit carboxyltransferase (CT). To obtain PCC with high enzyme activity, seven pccB genes encoding CT subunit from diverse microorganisms were expressed in recombinant E. coli, and PccB from Bacillus subtilis showed the highest activity in vitro. To further optimize this protein using directed evolution, a genetic screening system based on oxaloacetate availability was designed to enrich the active variants of PccBBs. Four amino acid substitutions (D46G, L97Q, N220I and I391T) proved of great assistance in PccBBs activity improvement, and a double mutant of PccBBs (N220I/I391T) showed a 94-fold increase of overall catalytic efficiency indicated by kcat/Km. Moreover, this PccBBs double mutant was applied in construction of new succinate biosynthetic pathway. This new pathway produces succinate from acetyl-CoA with fixation of two CO2 molecules, which was confirmed by isotope labeling experiment with NaH13CO3. Compared with previous succinate production based on carboxylation of phosphoenolpyruvate or pyruvate, this new pathway showed some advantages including higher CO2 fixation potentiality and availability under aerobic conditions. In summary, this study developed a PCC with high enzyme activity which can be widely used in biotechnology field, and also demonstrated the feasibility of new succinate biosynthetic pathway with two CO2 fixation reactions.

Case reports: three novel variants in PCCA and PCCB genes in Chinese patients with propionic acidemia.

BACKGROUND: Propionic acidemia (PA) is an autosomal recessive metabolic disorder caused by the deficiency of the mitochondrial protein propionyl-CoA carboxylase (PCC) and is associated with pathogenic variants in either of the two genes PCCA or PCCB. The present study aimed to identify the genetic cause of three Chinese patients with PA. CASE PRESENTATION: Three Chinese PA patients were diagnosed by using gas chromatography-mass spectrometry(GC-MS), tandem mass spectrometry (MS/MS) and molecular diagnostic methods. All patients had onset in the neonatal period. One patient died of infection and metabolic decompensation, and the other two had mild to moderate developmental delay/mental retardation. Mutation analysis of the PCCA gene identified that patient 1 carried the compound heterozygous c.1288C > T(p.R430X) and c.2002G > A(p.G668R), and patient 2 was homozygous for the c.1426C > T(p.R476X) mutation. Mutation analysis of the PCCB gene identified that patient 3 harbored the compound heterozygous mutations c.359_360del AT(p.Y120Cfs*40) and c.1398 + 1G > A. Among these mutations, three (c.1288C > T, c.359_360del AT and c.1398 + 1G > A) are novel. CONCLUSIONS: We reported three Chinese PA patients who had PCCA or PCCB mutants. Among them, in the PCCA gene, c.1288C > T(p.R430X) was a nonsense mutation, resulting in a truncated protein. c.359_360del AT was a frameshift mutation, leading to a p.Y120Cfs*40 change in the amino acid sequence in the PCCB protein. c.1398 + 1G > A was a splicing mutation, causing skipping of the exons 13-14. In conclusion, the novel mutations uncovered in this study will expands the mutation spectrum of PA.

Propionic acidemia identified in twin siblings conceived by in vitro fertilization (IVF) with parents who were unknown carriers of a PCCA mutation.

BACKGROUND: Propionic acidemia (PA) is a severe monogenic disorder characterized by a deficiency of the mitochondrial protein propionyl-CoA carboxylase (PCC) enzyme, which is caused by mutations in the PCCA or PCCB gene. Preconception carrier screening could provide couples with meaningful information for their reproductive options; however, it is not widely performed in China. CASE PRESENTATION: This report describes a case of dizygotic twin siblings conceived by in vitro fertilization (IVF) and diagnosed with propionic acidemia (PA). Their parents had no history of PA. Tandem mass spectrometry and urine gas chromatography/mass spectrometry (GC/MS) of the twin siblings revealed markedly elevated propionyl carnitine (C3), C3/C2, and 3-hydroxypropionate in the plasma and urine. Whole-exome sequencing was performed for the twin siblings. A homozygous missense mutation, c.2002G > A (p.Gly668Arg) in PCCA, was identified in the twin siblings. Sanger sequencing confirmed the homozygous mutation in the twin siblings and identified their parents as heterozygous carriers of the c.2002G > A mutation in PCCA. Both neonates in this case died. This is an emotionally and financially devastating outcome that could have been avoided with genetic carrier screening before conception. If couples are screened before IVF and found to be silent carriers, then reproductive options (such as preimplantation genetic diagnosis or prenatal diagnosis) can be offered to achieve a healthy newborn. CONCLUSION: This case is a reminder to infertile couples seeking IVF that it is beneficial to clarify whether they are silent carriers before undergoing IVF.

Identification of 34 novel mutations in propionic acidemia: Functional characterization of missense variants and phenotype associations.

Propionic acidemia (PA) is caused by mutations in the PCCA and PCCB genes, encoding α and ß subunits, respectively, of the mitochondrial enzyme propionyl-CoA carboxylase (PCC). Up to date, >200 pathogenic mutations have been identified, mostly missense defects. Genetic analysis in PA patients referred to the laboratory for the past 15 years identified 20 novel variants in the PCCA gene and 14 in the PCCB gene. 21 missense variants were predicted as probably disease-causing by different bioinformatics algorithms. Structural analysis in the available 3D model of the PCC enzyme indicated potential instability for most of them. Functional analysis in a eukaryotic system confirmed the pathogenic effect for the missense variants and for one amino acid deletion, as they all exhibited reduced or null PCC activity and protein levels compared to wild-type constructs. PCCB variants p.E168del, p.Q58P and p.I460T resulted in medium-high protein levels and no activity. Variants p.R230C and p.C712S in PCCA, and p.G188A, p.R272W and p.H534R in PCCB retained both partial PCC activity and medium-high protein levels. Available patients-derived fibroblasts carriers of some of these mutations were grown at 28 °C or 37 °C and a slight increase in PCC activity or protein could be detected in some cases at the folding-permissive conditions. Examination of available clinical data showed correlation of the results of the functional analysis with disease severity for most mutations, with some notable exceptions, confirming the notion that the final phenotypic outcome in PA is not easily predicted.

Autism spectrum disorders in propionic acidemia patients.

Propionic acidemia is the result of a deficiency in propionyl-CoA carboxylase activity. Chronic neurologic and cognitive complications frequently occur, but the psychiatric evolution of the disorder is not well documented. We conducted a pedopsychiatric evaluation of 19 children, adolescents and young adults, aged between 2 and 25 years, using ADI-R, CARS-T, as well as ADOS when autism spectrum disorder was suspected. Previous psychometric examinations were also taken into consideration. Thirteen patients had an IQ < 80. Two patients presented with autism and two additional patients with other autism spectrum disorders. Five patients did not fulfill diagnostic criteria for autism spectrum disorder but showed difficulties indicative of a broader autism phenotype (BAP). Four other patients had severe anxiety manifestations related to their disease. Two patients presented with acute psychotic episodes. The number of decompensations in the first 3 years of life was lower in patients with autism spectrum disorder or related symptoms. These patients were also older when they were assessed (median age of 15 years old versus 11 years old). There was no significant correlation between 3-hydroxypropionate levels during the first 6 years of life and autism spectrum disorder diagnosis. In conclusion, autism spectrum disorder is frequent in patients with propionic acidemia. These patients should undergo in-depth psychiatric evaluation and be screened for autism spectrum disorder. Further studies are needed to understand the underlying mechanisms.

Propionyl-CoA carboxylase pcca-1 and pccb-1 gene deletions in Caenorhabditis elegans globally impair mitochondrial energy metabolism.

Propionic acidemia (PA) is a classical inborn error of metabolism with high morbidity that results from the inability of the propionyl-CoA carboxylase (PCC) enzyme to convert propionyl-CoA to methylmalonyl-CoA. PA is inherited in an autosomal recessive fashion due to functional loss of both alleles of either PCCA or PCCB. These genes are highly conserved across evolutionarily diverse species and share extensive similarity with pcca-1 and pccb-1 in the nematode, Caenorhabditis elegans. Here, we report the global metabolic effects of deletion in a single PCC gene, either pcca-1 or pccb-1, in C. elegans. Animal lifespan was significantly reduced relative to wild-type worms in both mutant strains, although to a greater degree in pcca-1. Mitochondrial oxidative phosphorylation (OXPHOS) capacity and efficiency as determined by direct polarography of isolated mitochondria were also significantly reduced in both mutant strains. While in vivo quantitation of mitochondrial physiology was normal in pccb-1 mutants, pcca-1 deletion mutants had significantly increased mitochondrial matrix oxidant burden as well as significantly decreased mitochondrial membrane potential and mitochondrial content. Whole worm steady-state free amino acid profiling by UPLC revealed reduced levels in both mutant strains of the glutathione precursor cysteine, possibly suggestive of increased oxidative stress. Intermediary metabolic flux analysis by GC/MS with 1,6-13C2-glucose further showed both PCC deletion strains had decreased accumulation of a distal tricarboxylic acid (TCA) cycle metabolic intermediate (+1 malate), isotopic enrichment in a proximal TCA cycle intermediate (+1 citrate), and increased +1 lactate accumulation. GC/MS analysis further revealed accumulation in the PCC mutants of a small amount of 3-hydroxypropionate, which appeared to be metabolized in C. elegans to oxalate through a unique metabolic pathway. Collectively, these detailed metabolic investigations in translational PA model animals with genetic-based PCC deficiency reveal their significantly dysregulated energy metabolism at multiple levels, including reduced mitochondrial OXPHOS capacity, increased oxidative stress, and inhibition of distal TCA cycle flux, culminating in reduced animal lifespan. These findings demonstrate that the pathophysiology of PA extends well beyond what has classically been understood as a single PCC enzyme deficiency with toxic precursor accumulation, and suggest that therapeutically targeting the globally disrupted energy metabolism may offer novel treatment opportunities for PA. SUMMARY: Two C. elegans model animals of propionic acidemia with single-gene pcca-1 or pccb-1 deletions have reduced lifespan with significantly reduced mitochondrial energy metabolism and increased oxidative stress, reflecting the disease's broader pathophysiology beyond a single enzyme deficiency with toxic precursor accumulation.

Whole genome sequence study of cannabis dependence in two independent cohorts.

Recent advances in genome wide sequencing techniques and analytical methods allow for more comprehensive examinations of the genome than microarray-based genome-wide association studies (GWAS). The present report provides the first application of whole genome sequencing (WGS) to identify low frequency variants involved in cannabis dependence across two independent cohorts. The present study used low-coverage whole genome sequence data to conduct set-based association and enrichment analyses of low frequency variation in protein-coding regions as well as regulatory regions in relation to cannabis dependence. Two cohorts were studied: a population-based Native American tribal community consisting of 697 participants nested within large multi-generational pedigrees and a family-based sample of 1832 predominantly European ancestry participants largely nested within nuclear families. Participants in both samples were assessed for Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV) lifetime cannabis dependence, with 168 and 241 participants receiving a positive diagnosis in each sample, respectively. Sequence kernel association tests identified one protein-coding region, C1orf110 and one regulatory region in the MEF2B gene that achieved significance in a meta-analysis of both samples. A regulatory region within the PCCB gene, a gene previously associated with schizophrenia, exhibited a suggestive association. Finally, a significant enrichment of regions within or near genes with multiple splice variants or involved in cell adhesion or potassium channel activity were associated with cannabis dependence. This initial study demonstrates the potential utility of low pass whole genome sequencing for identifying genetic variants involved in the etiology of cannabis use disorders.

Propionyl-CoA carboxylase - A review.

Propionyl-CoA carboxylase (PCC) is the enzyme which catalyzes the carboxylation of propionyl-CoA to methylmalonyl-CoA and is encoded by the genes PCCA and PCCB to form a hetero-dodecamer. Dysfunction of PCC leads to the inherited metabolic disorder propionic acidemia, which can result in an affected individual presenting with metabolic acidosis, hyperammonemia, lethargy, vomiting and sometimes coma and death if not treated. Individuals with propionic acidemia also have a number of long term complications resulting from the dysfunction of the PCC enzyme. Here we present an overview of the current knowledge about the structure and function of PCC. We review an updated list of human variants which are published and provide an overview of the disease.