cblC Type Research Articles

Adult-onset combined methylmalonic acidemia and hyperhomocysteinemia, cblC type with aortic dissection and acute kidney injury: a case report

BackgroundCombined methylmalonic acidemia (MMA) and hyperhomocysteinemia, cobalamin C (cblC) type, also named cblC deficiency is a rare autosomal recessive genetic metabolic disease. It progressively causes neurological, hematologic, renal and other system dysfunction. The clinical manifestations are relatively different due to the onset time of disease.Case presentationThis report describes a rare case of a 26 year old man with cblC deficiency who developed life-threatening aortic dissection and acute kidney injury (AKI) and showed neuropsychiatric symptoms with elevated serum homocysteine and methylmalonic aciduria. After emergent operation and intramuscular cobalamin supplementation therapy, the male recovered from aortic dissection, neurological disorder and AKI. Finally, two previously published compound heterozygous variants, c.482G > A (p.R161Q) and c.658_660del (p.K220del) in the MMACHC gene were detected in this patient and he was confirmed to have cblC deficiency.ConclusionsPoor cognizance of presenting symptoms and biochemical features of adult onset cblC disease may cause delayed diagnosis and management. This case is the first to depict a case of adult-onset cblC deficiency with aortic dissection. This clinical finding may contribute to the diagnosis of cblC deficiency.

Clinical and Molecular Genetic Analysis with Methylmalonic Acidemia Combined with Homocystinuria.

Based on research, c.609G>A (p.W203X) is a universal mutation site for MMACHC in methylmalonic acidemia (MMA) combined with homocystinuria, cblC type (cblC disease), and c.467G>A (p.G156D) mutation in families with such disease have not yet been reported. To conduct clinical and molecular genetic analysis of a family with cblC disease. This work followed the Declaration of Helsinki. All testing methods were performed under the informed consent of our children patients' parents. A second-generation cblC family with 5 members, was selected as the research subject, including sick siblings and parents and an older sister with normal phenotype, given newborn screening for acylcarnitine spectrum via liquid chromatography tandem mass spectrometry (LC-MS/MS), and diagnosed through combining urine organic acid with homocysteine detection via gas chromatography-mass spectrometry (GC-MS) with second-generation gene sequencing technology. The peripheral blood of five family members was collected for genomic DNA extraction, and the changes were screened in disease-related MMACHC sequence via PCR and direct DNA sequencing. The family conformed to the autosomal recessive inheritance, the proband and younger sister were cblC patients, diagnosed in February and at 22d given relevant treatment. The proband died, whereas the younger sister received follow-up treatment. Their parents and sister had normal phenotype. In 2 cases, there was compound heterozygous mutation in MMACHC called c.609G>A (p.W203X) nonsense mutation and c.467G>A (p.G156D) missense mutation in exon 4, while the father with normal phenotype had heterozygous mutation c.609G>A in exon 4 coding area. In its protein, the 203rd amino acid changed from tryptophan to a stop codon (p.W203 x). The normal mother and sister had a heterozygous mutation c.467G>A in exon 4 coding area. In its protein, the 156th amino acid changed from glycine to aspartic acid (p.G156D). The cblC family results from c.609G>A (p.W203X) and c.467G>A (p.G156D) compound heterozygous mutations in MMACHC, which has a pathogenic impact.

Two Rare Mutations in Cases of Late-Onset cblC type

These cases suggest that even if combined methylmalonic aciduria with homocystinuria is a rare entity, its identification is essential so as to allow the initiation of an effective early treatment to avoid the pathophysiological progression and the serious clinical consequences of this disease, even in cases of late-onset cblC

Serum vitamin B12 is a promising auxiliary index for the diagnosis of methylmalonic acidemia in children: A single center study in China

Background and aimsVitamin B12 (cobalamin, VitB12) is an essential coenzyme of methylmalonyl-CoA mutase and methionine synthase. Variations in VitB12 metabolism, absorption, transport, or intake may cause changes in methylmalonic acidemia (MMA) biomarkers. We aimed to investigate whether serum Vitamin B12 levels could be used in the early detection of MMA. Materials and methodsWe included 241 children with MMA and 241 healthy matched controls. We measured serum VitB12 levels by an enzyme immunoassay and investigated the relationship between abnormal VitB12 levels and hematologic parameters as potential risk factors for MMA symptoms. ResultsCompared with controls, the serum levels of VitB12 were increased in the MMA group (p < 0.001). Serum VitB12 distinguished patients with MMA from healthy children (p < 0.001). Serum VitB12 combined with homocysteine and ammonia identified cblC and mut type MMA, respectively (p < 0.001). Homocysteine, folate, ammonia, NLR, and red blood cells contributed to serum VitB12 in cblC type MMA (p < 0.001); homocysteine, ammonia, and red blood cells, contributed in mut type MMA (p < 0.001); and elevated VitB12 was an independent predictor of MMA clinical onset (p < 0.001). ConclusionSerum VitB12 can be used as an early diagnostic biomarker for MMA in children.

Abnormal chondrocyte development in a zebrafish model of cblC syndrome restored by an MMACHC cobalamin binding mutant

Variants in the MMACHC gene cause combined methylmalonic acidemia and homocystinuria cblC type, the most common inborn error of intracellular cobalamin (vitamin B12) metabolism. cblC is associated with neurodevelopmental, hematological, ocular, and biochemical abnormalities. In a subset of patients, mild craniofacial dysmorphia has also been described. Mouse models of Mmachc deletion are embryonic lethal but cause severe craniofacial phenotypes such as facial clefts. MMACHC encodes an enzyme required for cobalamin processing and variants in this gene result in the accumulation of two metabolites: methylmalonic acid (MMA) and homocysteine (HC). Interestingly, other inborn errors of cobalamin metabolism, such as cblX syndrome, are associated with mild facial phenotypes. However, the presence and severity of MMA and HC accumulation in cblX syndrome is not consistent with the presence or absence of facial phenotypes. Thus, the mechanisms by which mutations in MMACHC cause craniofacial defects are yet to be completely elucidated. Here we have characterized the craniofacial phenotypes in a zebrafish model of cblC (hg13) and performed restoration experiments with either a wildtype or a cobalamin binding deficient MMACHC protein. Homozygous mutants did not display gross morphological defects in facial development but did have abnormal chondrocyte nuclear organization and an increase in the average number of neighboring cell contacts, both phenotypes were fully penetrant. Abnormal chondrocyte nuclear organization was not associated with defects in the localization of neural crest specific markers, sox10 (RFP transgene) or barx1. Both nuclear angles and the number of neighboring cell contacts were fully restored by wildtype MMACHC and a cobalamin binding deficient variant of the MMACHC protein. Collectively, these data suggest that mutation of MMACHC causes mild to moderate craniofacial phenotypes that are independent of cobalamin binding.

Methylmalonic acid levels in serum, exosomes, and urine and its association with cblC type methylmalonic acidemia-induced cognitive impairment.

The cblC type methylmalonic acidemia is the most common methylmalonic acidemia (MMA) in China. The biochemical characteristics of this disease include elevated methylmalonic acid and homocysteine (HCY), increased propionylcarnitine (C3), decreased free carnitine (C0). In this study, we aimed to clarify the roles of these biomarkers in cblC-MMA induced cognitive impairment and evaluate the capacity of methylmalonic acid in different fluids or exosomes to distinguish cblC-MMA induced cognitive impairment. 15 non-inherited hyperhomocysteinemia (HHcy) patients, 42 cblC-MMA patients and 57 age- and sex-matched healthy children were recruited in this study. The levels of HCY were detected by an automatic immune analyzer. The levels of acylcarnitines and methylmalonic acid were detected by tandem mass spectrometer. The main findings were all biomarkers as HCY, acylcarnitines and methylmalonic acid had capacities for distinguishing patients with cblC-MMA induced cognitive impairment from healthy children. The methylmalonic acid in different fluids or exosomes had good performances for distinguishing patients with cblC-MMA induced cognitive impairment from HHcy patients. The methylmalonic acid in serum exosomes and neuronal-derived exosomes were able to distinguishing cblC-MMA patients with cognitive impairment from patients without cognitive impairment. The methylmalonic acid in neuronal-derived exosomes might be helpful to evaluate the severity of cblC-MMA induced cognitive impairment. Methylmalonic acid levels in serum exosomes, especially in serum neuronal-derived exosomes, serve as potential biomarkers for distinguishing cblC-MMA induced cognitive impairment.

A Method for Quantitative Determination of Amino Acids and Organic Acids in Trace Random Urine and Preliminary Application in Research on Vitamin B12 Nutritional Status and Related Metabolism

Objective To develop a method for the quantification of amino acids and organic acids in trace urine by high performance liquid chromatography-tandem mass spectrometry.Methods Random urine samples(10 μl each)were precipitated by acetonitrile and underwent derivatization with 3 mol/L HCl in n-butanol.The analytes were separated by ACE Excel 2 AQ column(50×2.1 mm,2 μm).Electrospray ionization in positive ion mode was carried out and the analytes were detected in multiple reaction monitoring mode.According to existing guidelines,the method was systematically evaluated in terms of sensitivity,specificity,accuracy,precision,recovery,matrix effect,and stability.Then,the established method was employed to detect 19 target compounds in urine samples from 70 healthy children,27 children with suspected vitamin B12 deficiency,and 3 children with cblC type methylmalonic acidemia.Results The lower limit of quantification of the method for the 19 compounds ranged from 0.01 μmol/L to 1.00 μmol/L,and the calibration curves were linear,R2>0.990.The method showed good accuracy with relative error less than ±15% and the intra-day and intra-day precision less than 15%.The run time was 8 min.No obvious matrix effect was detected except for arginine,and the recovery ranged from 80.20% to 114.97%.The samples were stable after 8 h at room temperature and 3 freeze-thaw cycles.The measured values of the compounds in the urine of healthy children were within the children's reference intervals published by Labcorp.The levels of methylmalonic acid(P=0.030)and homocysteine(P<0.001)in the urine samples of children with suspected vitamin B12 deficiency were higher than those in healthy children.The levels of methylmalonic acid,methylcitric acid,and homocysteine in the urine samples of children with cblC type methylmalonic acidemia were 5.14-76.52 times higher than the median levels of healthy children. Conclusions The method established in this study has small sample demand and short run time,which can accurately quantify the levels of amino acids and metabolites in the urine of children.Moreover,it can provide data support for related studies about the metabolic characteristics of urine amino acids and their metabolites in children with vitamin B12 deficiency.

A teenager with combined methylmalonic aciduria and homocystinuria (CblC type) presenting with neurological symptoms and congenital heart diseases: a case report

ABSTRACT Combined methylmalonic acidemia and homocystinuria, is a rare autosomal recessive disorder due to defective intracellular cobalamin metabolism. We report an 18-year-old Chinese male who presented with hypermyotonia, seizures, and congenital heart diseases. Mutation analysis revealed c.365A>T and c.482 G>A mutations in the MMACHC gene, diagnosed with methylmalonic aciduria and homocystinuria (CblC type). After treatment with vitamin B12, L-carnitine, betaine, and folate, which resulted in an improvement in his clinical symptoms and laboratory values. This case emphasizes that inborn errors of metabolism should be considered for a teenager presenting with challenging or neurologic symptoms, especially when combined with unexplained heart diseases.

Factors affecting phenotypes in the patients with MMACHC gene c.609G>A homozygous variant cblC type methylmalonic acidemia combined with homocysteinuria

To investigate the factors affecting phenotypes in the patients of methylmalonic acidemia combined with homocysteinemia cblC type with MMACHC c.609G>A homologous variant. A retrospective study on the clinical manifestations, complications, treatment, and outcome in 164 patients of cblC type with MMACHC c.609G>A homologous variant was conducted. The patients were diagnosed by biochemical and genetic analysis from January 1998 to December 2020. Among the 164 patients, 2 cases were prenatally diagnosed and began treatment after birth. They are 3 and 12 years old with normal physical and mental development. Twenty-one cases were diagnosed by newborn screening. Among them, 15 cases had with normal development. They were treated from the age of two weeks at the asymptomatic period. Six cases began treatment aged 1 to 3 months after onset. Their development was delayed. One hundred and forty-one cases were clinically diagnosed. Their onset age ranges from a few minutes after birth to 6 years old. 110 cases had early-onset (78.0%). 31 cases had late-onset (22.0%). Five of them died. 24 patients lost to follow-up. Of the 141 clinically diagnosed patients, 130 (92.2%) with psychomotor retardation, 69 (48.9%) with epilepsy, 39 (27.7%) with anemia, 30 (21.3%) had visual impairment, 27 (19.1%) had hydrocephalus, 26 (18.4%) had feeding difficulties, 7 (5.0%) with liver damage, and 5 (3.5%) with metabolic syndrome. The frequency of hydrocephalus and seizures was significantly higher in the early-onset group. The urinary methylmalonic acid increased significantly in the patients with epilepsy. During the long-term follow-up, the level of plasma total homocysteine in the seizure-uncontrolled group was significantly higher than that in the seizure-controlled group, the difference had a statistical significance (P<0.05). Most of the patients with MMACHC c.609G>A homozygous variant had early-onset disease, with a high mortality and disability rate. If not treated in time, it will lead to neurological damage, resulting in epilepsy, mental retardation, hydrocephalus, and multiple organ damage. Pre-symptomatic diagnosis and treatment are crucial to prevent irreversible neurological damage. Neonatal screening and prenatal diagnosis are important to improve the outcome of the patients.

The Follow-Up of Chinese Patients in cblC Type Methylmalonic Acidemia Identified Through Expanded Newborn Screening.

Objective: The cblC type of combined methylmalonic acidemia and homocystinuria, an inherited disorder with variable phenotypes, is included in newborn screening (NBS) programs at multiple newborn screening centers in China. The present study aimed to investigate the long-term clinical benefits of screening individual. Methods: A national, retrospective multi-center study of infants with confirmed cblC defect identified by NBS between 2004 and 2020 was conducted. We collected a large cohort of 538 patients and investigated their clinical data in detail, including disease onset, biochemical metabolites, and gene variation, and explored different factors on the prognosis. Results: The long-term outcomes of all patients were evaluated, representing 44.6% for poor outcomes. In our comparison of patients with already occurring clinical signs before treatment to asymptomatic ones, the incidence of intellectual impairment, movement disorders, ocular complications, hydrocephalus, and death were significantly different (p < 0.01). The presence of disease onset [Odd ratio (OR) 12.39, 95% CI 5.15–29.81; p = 0.000], variants of c.609G>A (OR 2.55, 95% CI 1.49–4.35; p = 0.001), and c.567dupT (OR 2.28, 95% CI 1.03–5.05; p = 0.042) were independently associated with poor outcomes, especially for neurodevelopmental deterioration. Conclusion: NBS, avoiding major disease-related events and allowing an earlier treatment initiation, appeared to have protective effects on the prognosis of infants with cblC defect.

Noninvasive Prenatal Testing of Methylmalonic Acidemia cblC Type Using the cSMART Assay for MMACHC Gene Mutations.

Noninvasive prenatal testing (NIPT) for monogenic disorders has been developed in recent years; however, there are still significant technical and analytical challenges for clinical use. The clinical feasibility of NIPT for methylmalonic acidemia cblC type (cblC type MMA) was investigated using our circulating single-molecule amplification and re-sequencing technology (cSMART). Trios molecular diagnosis was performed in 29 cblC type MMA-affected children and their parents by traditional Sanger sequencing. In the second pregnancy, invasive prenatal diagnosis (IPD) of the pathogenic MMACHC gene was used to determine fetal genotypes, and NIPT was performed using a novel MMACHC gene–specific cSMART assay. Maternal–fetal genotypes were deduced based on the mutation ratio in maternal plasma DNA. Concordance of fetal genotypes between IPD and NIPT, and the sensitivity and specificity of NIPT were determined. After removing two cases with a low P value or reads, the concordance ratio for NIPT and IPD was 100.00% (27/27), and the sensitivity and specificity were 100.00% (54.07–100.00%) and 100.00% (83.89–100.00%), respectively. This study demonstrates that NIPT using the cSMART assay for cblC type MMA was accurate in detecting fetal genotypes. cSMART has a potential clinical application as a prenatal diagnosis and screening tool for carrier and low-risk genotypes of cblC type MMA and other monogenic diseases.

Clinical features and outcomes of patients with cblC type methylmalonic acidemia carrying gene c.609G>A mutation.

To explore the clinical features and long-term outcomes of patients with cblC type methylmalonic acidemia (MMA) carrying c.609G>A (p.W203X) mutation of gene. The clinical and laboratory findings of 720 patients with MMA carrying the c.609G>A mutation were retrospectively analyzed. There were 172 cases carrying homozygous mutations of c.609G>A (group A), 169 cases carrying compound heterozygous mutations of c.609G>A with c.482G>A (p.R161Q), c.80A>G or c.394C>T (p.R132X) (group B), and 379 cases carrying compound heterozygous mutations of c.609G>A with c.658_660delAAG(p.K220del), c.315A>Tor c.567dupT(p.I190fs13)(group C).The clinical manifestations, the level of blood acylcarnitine, homocysteine and urinary organic acid, and the therapeutic efficacy were compared among groups. Logistic regression was used to analyze the factors influencing the prognosis of patients. There were 306 patients (42.5%) detected from newborn screening, including 156 cases with disease onset; and 414 patients were not detected from the screening, among whom 10 cases were diagnosed by testing after the sibling confirmed, and the remaining 404 were clinical cases. In 560 patients with disease onset, the median onset age is (3 days to 20 years). The onset age of patients in group B was later than that in group A and group C (<0.01). Patients aged mostly manifested as vomiting, diarrhea, feeding difficulties and convulsions, while those year mostly manifested as movement disorders and mental retardation. Patients with renal disease all carried mutations of c.80A>G or c.482G>A, and patients with pulmonary hypertension all carried c.80A>G mutations. A total of 621 cases had long-term follow-up, 156 cases (25.1%) developed well, 433 cases (69.7%) had development delay and 32 cases (5.2%) died. The available data of 559 cases were analyzed by logistic regression, and the results showed that the neonatal screening, disease onset, age of onset and gene mutation site were significantly associated with the prognosis of patients (<0.05 or <0.01). The c.609G>A mutation in gene is associated with early-onset MMA, and most patients, clinical onset occurred within 1 month after birth. The neonatal screening and early treatment can improve the prognosis of patients,whereas clinical onset is unfavorable for prognosis. Patients with c.609G>A homozygous mutation have a worse prognosis than those with the compound heterozygous mutation of c.609G>A with other mutations.

PRDX1 gene-related epi-cblC disease is a common type of inborn error of cobalamin metabolism with mono- or bi-allelic MMACHC epimutations

BackgroundThe role of epigenetics in inborn errors of metabolism (IEMs) is poorly investigated. Epigenetic changes can contribute to clinical heterogeneity of affected patients but could also be underestimated determining factors in the occurrence of IEMs. An epigenetic cause of IEMs has been recently described for the autosomal recessive methylmalonic aciduria and homocystinuria, cblC type (cblC disease), and it has been named epi-cblC. Epi-cblC has been reported in association with compound heterozygosity for a genetic variant and an epimutation at the MMACHC locus, which is secondary to a splicing variant (c.515-1G > T or c.515-2A > T) at the adjacent PRDX1 gene. Both these variants cause aberrant antisense transcription and cis-hypermethylation of the MMACHC gene promotor with subsequent silencing. Until now, only nine epi-cblC patients have been reported.MethodsWe report clinical/biochemical assessment, MMACHC/PRDX1 gene sequencing and genome-wide DNA methylation profiling in 11 cblC patients who had an inconclusive MMACHC gene testing. We also compare clinical phenotype of epi-cblC patients with that of canonical cblC patients.ResultsAll patients turned out to have the epi-cblC disease. One patient had a bi-allelic MMACHC epimutation due to the homozygous PRDX1:c.515-1G > T variant transmitted by both parents. We found that the bi-allelic epimutation produces the complete silencing of MMACHC in the patient’s fibroblasts. The remaining ten patients had a mono-allelic MMACHC epimutation, due to the heterozygous PRDX1:c.515-1G > T, in association with a mono-allelic MMACHC genetic variant. Epi-cblC disease has accounted for about 13% of cblC cases diagnosed by newborn screening in the Tuscany and Umbria regions since November 2001. Comparative analysis showed that clinical phenotype of epi-cblC patients is similar to that of canonical cblC patients.ConclusionsWe provide evidence that epi-cblC is an underestimated cause of inborn errors of cobalamin metabolism and describe the first instance of epi-cblC due to a bi-allelic MMACHC epimutation. MMACHC epimutation/PRDX1 mutation analyses should be part of routine genetic testing for all patients presenting with a metabolic phenotype that combines methylmalonic aciduria and homocystinuria.

Absence of MMACHC in peripheral retinal cells does not lead to an ocular phenotype in mice

Combined methylmalonic aciduria with homocystinuria (cblC type) is a rare disease caused by mutations in the MMACHC gene. MMACHC encodes an enzyme crucial for intracellular vitamin B12 metabolism, leading to the accumulation of toxic metabolites e.g. methylmalonic acid (MMA) and homocysteine (Hcy), and secondary disturbances in folate and one-carbon metabolism when not fully functional. Patients with cblC deficiency often present in the neonatal or early childhood period with a severe multisystem pathology, which comprises a broad spectrum of treatment-resistant ophthalmological phenotypes, including retinal degeneration, impaired vision, and vascular changes. To examine the potential function of MMACHC in the retina and how its loss may impact disease, we performed gene expression studies in human and mouse, which showed that local expression of MMACHC in the retina and retinal pigment epithelium is relatively stable over time. To study whether functional MMACHC is required for retinal function and tissue integrity, we generated a transgenic mouse lacking Mmachc expression in cells of the peripheral retina. Characterization of this mouse revealed accumulation of cblC disease related metabolites, including MMA and the folate-dependent purine synthesis intermediates AICA-riboside and SAICA-riboside in the retina. Nevertheless, fundus appearance, morphology, vasculature, and cellular composition of the retina, as well as ocular function, remained normal in mice up to 6 or 12 months of age. Our data indicates that peripheral retinal neurons do not require intrinsic expression of Mmachc for survival and function and questions whether a local MMACHC deficiency is responsible for the retinal phenotypes in patients.

Combined Genome, Transcriptome and Metabolome Analysis in the Diagnosis of Childhood Cerebellar Ataxia.

Ataxia in children is a common clinical sign of numerous neurological disorders consisting of impaired coordination of voluntary muscle movement. Its most common form, cerebellar ataxia, describes a heterogeneous array of neurologic conditions with uncountable causes broadly divided as acquired or genetic. Numerous genetic disorders are associated with chronic progressive ataxia, which complicates clinical management, particularly on the diagnostic stage. Advances in omics technologies enable improvements in clinical practice and research, so we proposed a multi-omics approach to aid in the genetic diagnosis and molecular elucidation of an undiagnosed infantile condition of chronic progressive cerebellar ataxia. Using whole-exome sequencing, RNA-seq, and untargeted metabolomics, we identified three clinically relevant mutations (rs141471029, rs191582628 and rs398124292) and an altered metabolic profile in our patient. Two POLR1C diagnostic variants already classified as pathogenic were found, and a diagnosis of hypomyelinating leukodystrophy was achieved. A mutation on the MMACHC gene, known to be associated with methylmalonic aciduria and homocystinuria cblC type, was also found. Additionally, preliminary metabolome analysis revealed alterations in our patient’s amino acid, fatty acid and carbohydrate metabolism. Our findings provided a definitive genetic diagnosis reinforcing the association between POLR1C mutations and hypomyelinating leukodystrophy and highlighted the relevance of multi-omics approaches to the disease.

Mouse models to study the pathophysiology of combined methylmalonic acidemia and homocystinuria, cblC type

Combined methylmalonic acidemia and homocystinuria, cblC type, is the most common inherited disorder of cobalamin metabolism and is characterized by severe fetal developmental defects primarily impacting the central nervous system, hematopoietic system, and heart. CblC was previously shown to be due to mutations in the MMACHC gene, which encodes a protein thought to function in intracellular cobalamin trafficking and biosynthesis of adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl). These coenzymes are required for the production of succinyl-CoA and methionine, respectively. However, it is currently unclear whether additional roles for MMACHC exist outside of cobalamin metabolism. Furthermore, due to a lack of sufficient animal models, the exact pathophysiology of cblC remains unknown. Here, we report the generation and characterization of two new mouse models to study the role of MMACHC in vivo. CRISPR/Cas9 genome editing was used to develop a Mmachc floxed allele (Mmachcflox/flox), which we validated as a conditional null. For a gain-of-function approach, we generated a transgenic mouse line that over-expresses functional Mmachc (Mmachc-OE+/tg) capable of rescuing Mmachc homozygous mutant lethality. Surprisingly, our data also suggest that these mice may exhibit a partially penetrant maternal-effect rescue, which might have implications for in utero therapeutic interventions to treat cblC. Both the Mmachcflox/flox and Mmachc-OE+/tg mouse models will be valuable resources for understanding the biological roles of MMACHC in a variety of tissue contexts and allow for deeper understanding of the pathophysiology of cblC.

Screening for carriers of pathogenic genes for methylmalonic acidemia and Wilson's disease in neonates in Qingdao

Objective: To investigate the carrier frequency of pathogenic genes for methylmalonic acidemia and Wilson's disease in neonates in Qingdao. Methods: In this cross-sectional study, using computer random sampling, 5 020 neonates from the neonatal screening center in Qingdao area from June 2016 to December 2018 were selected, and 5 012 of them were included in the carrier screening study.DNA was extracted from dried blood stain specimens used in the screening of newborns. Multiplex PCR combined with next generation sequencing were used for gene detection of MMACHC gene, MUT gene and ATP7B gene. The carrying rate of hotspots of each gene were calculated, and binomial distribution method was used to calculate 95% confidence interval of pathogenic gene carrying rate. Results: A total of 5 012 neonates completed the screening for carriers of disease-causing genes, of which 5 006 neonates completed the screening of two diseases and the remaining 6 neonates completed the screening of Wilson disease only.For ATP7B gene, the carrier frequency of the 12 hot spot mutations was 1.46% (73/5 012),and the 95% confidence interval was 1.16%-1.83%. For MMACHC gene and MUT gene, carrier frequency of 18 hot spot mutations was 2.50% (125/5 006) , and the 95% confidence interval was 2.10%-2.97%, among which cblC type accounted for 87.2% and the MUT pathogenic gene accounted for 12.8%. Conclusion: The carrier frequency of methylmalonic acidemia and Wilson's disease are both high in the neonatal population in Qingdao.

CblX is a New Cobalamin Syndrome Affecting Craniofacial Development

Combined methylmalonic acidemia and homocystinuria (cblC type), an inherited disorder of cobalamin (vitamin B12) metabolism, is a rare metabolic and multi‐systemic disease caused by mutations in MMACHC. Patients with cblC can have severe neurodevelopmental defects including microcephaly, hydrocephaly, and seizures as well as renal, cardiac and hematological defects. Recently, two new variants of cblC were discovered and termed cblX and cblX‐like. Rather than being due to mutations in MMACHC, cblX and cblX‐like result from homozygous mutations in the transcription cofactor HCFC1 and its transcription factor partner RONIN (THAP11), respectively. Patients with either HCFC1 or RONIN mutations were shown to have a dramatic reduction in MMACHC transcription. We have known that HCFC1 is an obligatory partner for RONIN and we have previously shown that the HCFC1/RONIN transcriptional complex directly regulates mouse Mmachc expression. These findings suggest that cblX and cblX‐like disorders comprise a novel family of rare and severe cblC‐like disorders that are transcriptional in nature. To better understand the cellular and molecular mechanisms underlying the pathophysiology of these devastating neurodevelopmental diseases, we have generated Hcfc1A115V and RoninF80L mice, which have the same point mutations observed in cblX and cblX‐like patients. Both Hcfc1Y/A115V hemizygous and RoninF80L/F80L homozygous mice exhibit defects in cobalamin metabolism consistent with an inherited vitamin B12 disorder, as well as defects that recapitulate those observed in the human cblX and cblX‐like patients, including severe brain developmental defects, cardiac malformations, and anemia. Additionally, these mice also exhibit craniofacial deformities, a developmental phenotype that has not been previously linked to vitamin B12. Our data identifies, for the first time, a role for RONIN/HCFC1 in craniofacial development. Together, the phenotypic and molecular data confirm that the RoninF80L and Hcfc1A115V mouse models will serve as powerful tools to further uncover the pathophysiology of this complex family of diseases, as well as to achieve a better understanding of the complexities of craniofacial development.Support or Funding InformationThis work is supported by R01 DE028298.

Clinical analysis of methylmalonic acidemia and hyperhomocysteinemia with diffuse lung disease as an initial or main presentation

Objective: To improve the awareness of methylmalonic acidemia and hyperhomocysteinemia with diffuse lung disease as an initial or main presentation. Methods: A retrospective analysis of the clinical manifestations, radiological features, laboratory tests, genetic variations, treatments and prognoses was conducted in six children presented with diffuse lung disease and finally diagnosed with methylmalonic acidemia and hyperhomocysteinemia in Ward 2 of Department of Respiratory Diseases, Beijing Children's Hospital, from August 2017 to November 2018. Results: Six children were included in this study. Two children were male and four were female. The average age of onset was 28 months. The mean age at diagnosis was 34 months. The average interval from onset to diagnosis was 6 months. Four children who underwent genetic tests were found to have variants of gene MMACHC and diagnosed with CblC type. All children had respiratory symptoms and signs as initial or main presentation, which were tachypnea (5 cases), exercise intolerance (5 cases), cough (4 cases), cyanosis (4 cases), clubbing (4 cases), dyspnea (3 cases) and retractions (3 cases). Pulmonary arterial hypertension was found in all six children. Pericardial effusion (4 cases), kidney involvement (3 cases), nervous system involvement (3 cases), gastrointestinal system involvement (3 cases) and anemia (2 cases) also coexisted. The high resolution computed tomography (HRCT) features included dilated pulmonary artery (6 cases), ground-glass opacities (4 cases), diffuse poorly defined ground-glass centrilobular nodules (3 cases), pleural effusion (3 cases), thickening of interlobular septum (2 cases), etc. All children had an elevated concentration of methylmalonic acid in urine and homocysteine in plasma. Genetic tests were performed in four patients, and MMACHC genetic mutations were found in all of them. Clinical manifestations, HRCT features and pulmonary arterial hypertension turned better in five children after treatment. One patient who was not regularly followed-up died. Conclusions: Pulmonary involvement including diffuse lung disease and pulmonary arterial hypertension could coexist with methylmalonic acidemia and hyperhomocysteinemia, which may have respiratory symptoms and signs as the initial or main presentation. Characteristic HRCT features were found in some patients. Plasma homocysteine test is a quick method for screening the disease in children with diffuse lung disease and (or) pulmonary arterial hypertension. Both diffuse lung disease and pulmonary arterial hypertension may turn better after treatment.

Clinical analysis and outcome of patients with c. 482G >A variant of MMACHC gene in cblC type methylmalonic acidemia

Objective To explore the clinical manifestations, treatment and outcomes of patients with c. 482G>A(p.R161Q)variant of MMACHC gene in cblC type methylmalonic acidemia(MMA). Methods The clinical manifestations, mass spectrometry results, genotypes, treatment and outcomes of 75 patients with cblC type MMA carrying c. 482G>A(p.R161Q)variant were retrospectively analyzed. Results Of the 75 patients, 57(76%)were from newborn screening and one of them had an onset. Among the rest 18 unscreened patients, 2 were diagnosed after their full sisters′ or brothers′ diagnosis, the others were clinical patients. There were 17 clinical patients, with the medium age of onset 12 years old(10 days~26 years old). 12 late onset patients(70.6%)presented with poor academic performance, memory loss, poor expression, and decreased exercise capacity, while 5 early onset patients(29.4%)presented with convulsion and delay of development. All patients were vitamin B12-responsive. The levels of blood propionylcarnitine, the ratio of propionylcarnitine to acetylcarnitine, urinary methylmalonic acid and methyldecanoic acid, and plasma homocysteine were significantly decreased after treatment(P< 0.01). All patients diagnosed from newborn screening had normal development. However, only 3 clinical patients had a rather normal outcomes and the others remained different levels of intelligence and(or)motor dysfunction after treatment. Conclusion The c. 482G>A(p.R161Q)variant of MMACHC gene is associated with late onset cblC type MMA. Patients with this variant have a better response to hydroxycobalamin than other variants. The outcome of patients diagnosed from the newborn screening is good. When symptoms occur, the disability rate is often high. Therefore, newborn screening is a recommended method to prevent this disease. Key words: Methylmalonic acidemia; MMACHC gene; Methylmalonic acid; Propionylcarnitine