Bi-allelic ATG4D variants are associated with a neurodevelopmental disorder characterized by speech and motor impairment.

Autophagy regulates the degradation of damaged organelles and protein aggregates, and is critical for neuronal development, homeostasis, and maintenance, yet few neurodevelopmental disorders have been associated with pathogenic variants in genes encoding autophagy-related proteins. We report three individuals from two unrelated families with a neurodevelopmental disorder characterized by speech and motor impairment, and similar facial characteristics. Rare, conserved, bi-allelic variants were identified in ATG4D, encoding one of four ATG4 cysteine proteases important for autophagosome biogenesis, a hallmark of autophagy. Autophagosome biogenesis and induction of autophagy were intact in cells from affected individuals. However, studies evaluating the predominant substrate of ATG4D, GABARAPL1, demonstrated that three of the four ATG4D patient variants functionally impair ATG4D activity. GABARAPL1 is cleaved or "primed" by ATG4D and an in vitro GABARAPL1 priming assay revealed decreased priming activity for three of the four ATG4D variants. Furthermore, a rescue experiment performed in an ATG4 tetra knockout cell line, in which all four ATG4 isoforms were knocked out by gene editing, showed decreased GABARAPL1 priming activity for the two ATG4D missense variants located in the cysteine protease domain required for priming, suggesting that these variants impair the function of ATG4D. The clinical, bioinformatic, and functional data suggest that bi-allelic loss-of-function variants in ATG4D contribute to the pathogenesis of this syndromic neurodevelopmental disorder.

Homozygous splice-variants in human ARV1 cause GPI-anchor synthesis deficiency.

BACKGROUND: Mutations in the ARV1 Homolog, Fatty Acid Homeostasis Modulator (ARV1), have recently been described in association with early infantile epileptic encephalopathy 38. Affected individuals presented with epilepsy, ataxia, profound intellectual disability, visual impairment, and central hypotonia. In S. cerevisiae, Arv1 is thought to be involved in sphingolipid metabolism and glycophosphatidylinositol (GPI)-anchor synthesis. The function of ARV1 in human cells, however, has not been elucidated. METHODS: Mutations were discovered through whole exome sequencing and alternate splicing was validated on the cDNA level. Expression of the variants was determined by qPCR and Western blot. Expression of GPI-anchored proteins on neutrophils and fibroblasts was analyzed by FACS and immunofluorescence microscopy, respectively. RESULTS: Here we describe seven patients from two unrelated families with biallelic splice mutations in ARV1. The patients presented with early onset epilepsy, global developmental delays, profound hypotonia, delayed speech development, cortical visual impairment, and severe generalized cerebral and cerebellar atrophy. The splice variants resulted in decreased ARV1 expression and significant decreases in GPI-anchored protein on the membranes of neutrophils and fibroblasts, indicating that the loss of ARV1 results in impaired GPI-anchor synthesis. CONCLUSION: Loss of GPI-anchored proteins on our patients' cells confirms that the yeast Arv1 function of GPI-anchor synthesis is conserved in humans. Overlap between the phenotypes in our patients and those reported for other GPI-anchor disorders suggests that ARV1-deficiency is a GPI-anchor synthesis disorder.

Cerebral and portal vein thrombosis, macrocephaly and atypical absence seizures in Glycosylphosphatidyl inositol deficiency due to a PIGM promoter mutation.

Defects of the glycosylphosphatidylinositol (GPI) biosynthesis pathway constitute an emerging subgroup of congenital disorders of glycosylation with heterogeneous phenotypes. A mutation in the promoter of PIGM, resulting in a syndrome with portal vein thrombosis and persistent absence seizures, was previously described in three patients. We now report four additional patients in two unrelated families, with further clinical, biochemical and molecular delineation of this unique entity. We also describe the first prenatal diagnosis of PIGM deficiency, allowing characterization of the natural history of the disease from birth. The patients described herein expand the phenotypic spectrum of PIGM deficiency to include macrocephaly and infantile-onset cerebrovascular thrombotic events. Finally, we offer insights regarding targeted treatment of this rare disorder with sodium phenylbutyrate.

Lysosomal Storage and Albinism Due to Effects of a De Novo CLCN7 Variant on Lysosomal Acidification.

Optimal lysosome function requires maintenance of an acidic pH maintained by proton pumps in combination with a counterion transporter such as the Cl-/H+ exchanger, CLCN7 (ClC-7), encoded by CLCN7. The role of ClC-7 in maintaining lysosomal pH has been controversial. In this paper, we performed clinical and genetic evaluations of two children of different ethnicities. Both children had delayed myelination and development, organomegaly, and hypopigmentation, but neither had osteopetrosis. Whole-exome and -genome sequencing revealed a de novo c.2144A>G variant in CLCN7 in both affected children. This p.Tyr715Cys variant, located in the C-terminal domain of ClC-7, resulted in increased outward currents when it was heterologously expressed in Xenopus oocytes. Fibroblasts from probands displayed a lysosomal pH approximately 0.2 units lower than that of control cells, and treatment with chloroquine normalized the pH. Primary fibroblasts from both probands also exhibited markedly enlarged intracellular vacuoles; this finding was recapitulated by the overexpression of human p.Tyr715Cys CLCN7 in control fibroblasts, reflecting the dominant, gain-of-function nature of the variant. A mouse harboring the knock-in Clcn7 variant exhibited hypopigmentation, hepatomegaly resulting from abnormal storage, and enlarged vacuoles in cultured fibroblasts. Our results show that p.Tyr715Cys is a gain-of-function CLCN7 variant associated with developmental delay, organomegaly, and hypopigmentation resulting from lysosomal hyperacidity, abnormal storage, and enlarged intracellular vacuoles. Our data supports the hypothesis that the ClC-7 antiporter plays a critical role in maintaining lysosomal pH.

Novel mutations in CLN6 cause late-infantile neuronal ceroid lipofuscinosis without visual impairment in two unrelated patients.

CLN6 is a transmembrane protein located in the endoplasmic reticulum that is involved in lysosomal acidification. Mutations in CLN6 cause late-infantile neuronal ceroid lipofuscinosis (LINCL), and teenage and adult onset NCL without visual impairment. Here we describe two pediatric patients with LINCL from unrelated families who were evaluated at the National Institutes of Health. Both children exhibited typical phenotypes associated with LINCL except that they lacked the expected visual impairment. Whole exome sequencing identified novel biallelic mutations in CLN6, i.e., c.218-220dupGGT (p.Trp73dup) and c.296A > G (p.Lys99Arg) in Proband 1 and homozygous c.723G > T (p.Met241Ile) in Proband 2. Expression analysis in dermal fibroblasts showed a small increase in CLN6 protein levels. Electron micrographs of these fibroblasts demonstrated large numbers of small membrane-bound vesicles, in addition to lipofuscin deposits. LysoTracker™ Red intensity was increased in fibroblasts from both patients. This study supports a role for CLN6 in lysosomal homeostasis, and highlights the importance of considering CLN6 mutations in the diagnosis of Batten Disease even in patients with normal vision.

Early infantile-onset epileptic encephalopathy 28 due to a homozygous microdeletion involving the WWOX gene in a region of uniparental disomy.

The genetic etiologies of many rare disorders, including early infantile epileptic encephalopathies, are largely undiagnosed. A 6-year-old girl was admitted to the National Institutes of Health Undiagnosed Diseases Program with profound intellectual disability, infantile-onset seizures, chronic respiratory failure, facial dysmorphisms, skeletal abnormalities, and atrial septum defect. A large region of homozygosity was discovered on chromosome 16, spanning 16q22.1-16q24.3' caused by uniparental disomy (UPD) that included a maternally inherited homozygous microdeletion covering exon 6 of WWOX (NM_016373.3). mRNA expression analysis revealed that the deletion led to nonsense-mediated decay of the NM_016373.3 transcript; the exon 6 of an alternative transcript (NM_130791.3), lacking the short-chain dehydrogenase, was utilized. The microdeletion in WWOX explains the seizures and intellectual disability, while pathogenic variants in another gene, HSPG2, are likely responsible for the patient's skeletal abnormalities. This report describes a rare autosomal recessive disorder with multiple genetic etiologies, one of which involves UPD.

Glycomics in rare diseases: from diagnosis tomechanism.

The National Institutes of Health (NIH) Undiagnosed Diseases Program (UDP) studies rare genetic disorders not only to achieve diagnoses, but to understand human biology. To ascertain the contribution of protein glycosylation to rare diseases, the NIH UDP used mass spectrometry to agnostically identify abnormalities of N-linked and O-linked glycans in plasma and free oligosaccharides in the urine of 207 patients. 60% of UDP patients had a glycome profile that deviated from control values in at least 1 fluid. Additional evaluation of the fibroblast glycome in 66 patients with abnormalities in plasma and/or urine revealed a consistent glycome phenotype in 83% of these cases. Many of these patients may have secondary glycosylation defects, since it is unlikely that they all have congenital disorders of glycosylation (CDGs). In fact, whole exome sequencing revealed only a few patients with CDGs, along with several others having disorders indirectly altering glycosylation. In summary, we describe a biochemical phenotyping screen to identify defects in protein glycosylation that can elucidate mechanisms of disease among NIH UDP patients.

A Recurrent De Novo Heterozygous COG4 Substitution Leads to Saul-Wilson Syndrome, Disrupted Vesicular Trafficking, and Altered Proteoglycan Glycosylation.

The conserved oligomeric Golgi (COG) complex is involved in intracellular vesicular transport, and is composed of eight subunits distributed in two lobes, lobe A (COG1-4) and lobe B (COG5-8). We describe fourteen individuals with Saul-Wilson syndrome, a rare form of primordial dwarfism with characteristic facial and radiographic features. All affected subjects harbored heterozygous de novo variants in COG4, giving rise to the same recurrent amino acid substitution (p.Gly516Arg). Affected individuals' fibroblasts, whose COG4 mRNA and protein were not decreased, exhibited delayed anterograde vesicular trafficking from the ER to the Golgi and accelerated retrograde vesicular recycling from the Golgi to the ER. This altered steady-state equilibrium led to a decrease in Golgi volume, as well as morphologic abnormalities with collapse of the Golgi stacks. Despite these abnormalities of the Golgi apparatus, protein glycosylation in sera and fibroblasts from affected subjects was not notably altered, but decorin, a proteoglycan secreted into the extracellular matrix, showed altered Golgi-dependent glycosylation. In summary, we define a specific heterozygous COG4 substitution as the molecular basis of Saul-Wilson syndrome, a rare skeletal dysplasia distinct from biallelic COG4-CDG.

Cover Image, Volume 173A, Number 12, December 2017.

The cover image, by Isabel Hardee et al., is based on the Clinical Report Defective ciliogenesis in INPP5E-related Joubert syndrome, DOI: 10.1002/ajmg.a.38376. Design Credit: Darryl Leja.

Defective ciliogenesis in INPP5E-related Joubert syndrome.

Joubert syndrome is a neurodevelopmental disorder, characterized by malformation of the mid and hindbrain leading to the pathognomonic molar tooth appearance of the brainstem and cerebellum on axial MRI. Core clinical manifestations include hypotonia, tachypnea/apnea, ataxia, ocular motor apraxia, and developmental delay of varying degrees. In addition, a subset of patients has retinal dystrophy, chorioretinal colobomas, hepatorenal fibrocystic disease, and polydactyly. Joubert syndrome exhibits genetic heterogeneity, with mutations identified in more than 30 genes, including INPP5E, a gene encoding inositol polyphosphate 5-phosphatase E, which is important in the development and stability of the primary cilium. Here, we report the detailed clinical phenotypes of two sisters with a novel homozygous variant in INPP5E (NM_019892.4: c.1565G>C, NP_063945.2: p.Gly552Ala), expanding the phenotype associated with Joubert syndrome type 1. Expression studies using patient-derived fibroblasts showed changes in mRNA and protein levels. Analysis of fibroblasts from patients revealed that a significant number of cells had shorter or no cilia, indicating defects in ciliogenesis, and cilia maintenance.

Defining Disease, Diagnosis, and Translational Medicine within a Homeostatic Perturbation Paradigm: The National Institutes of Health Undiagnosed Diseases Program Experience.

Traditionally, the use of genomic information for personalized medical decisions relies on prior discovery and validation of genotype-phenotype associations. This approach constrains care for patients presenting with undescribed problems. The National Institutes of Health (NIH) Undiagnosed Diseases Program (UDP) hypothesized that defining disease as maladaptation to an ecological niche allows delineation of a logical framework to diagnose and evaluate such patients. Herein, we present the philosophical bases, methodologies, and processes implemented by the NIH UDP. The NIH UDP incorporated use of the Human Phenotype Ontology, developed a genomic alignment strategy cognizant of parental genotypes, pursued agnostic biochemical analyses, implemented functional validation, and established virtual villages of global experts. This systematic approach provided a foundation for the diagnostic or non-diagnostic answers provided to patients and serves as a paradigm for scalable translational research.

Abnormal glycosylation in Joubert syndrome type 10.

BACKGROUND: The discovery of disease pathogenesis requires systematic agnostic screening of multiple homeostatic processes that may become deregulated. We illustrate this principle in the evaluation and diagnosis of a 5-year-old boy with Joubert syndrome type 10 (JBTS10). He carried the OFD1 mutation p.Gln886Lysfs*2 (NM_003611.2: c.2656del) and manifested features of Joubert syndrome. METHODS: We integrated exome sequencing, MALDI-TOF mass spectrometry analyses of plasma and cultured dermal fibroblasts glycomes, and full clinical evaluation of the proband. Analyses of cilia formation and lectin staining were performed by immunofluorescence. Measurement of cellular nucleotide sugar levels was performed with high-performance anion-exchange chromatography with pulsed amperometric detection. Statistical analyses utilized the Student's and Fisher's exact t tests. RESULTS: Glycome analyses of plasma and cultured dermal fibroblasts identified abnormal N- and O-linked glycosylation profiles. These findings replicated in two unrelated males with OFD1 mutations. Cultured fibroblasts from affected individuals had a defect in ciliogenesis. The proband's fibroblasts also had an abnormally elevated nuclear sialylation signature and increased total cellular levels of CMP-sialic acid. Ciliogenesis and each glycosylation anomaly were rescued by expression of wild-type OFD1. CONCLUSIONS: The rescue of ciliogenesis and glycosylation upon reintroduction of WT OFD1 suggests that both contribute to the pathogenesis of JBTS10.

Prospective phenotyping of NGLY1-CDDG, the first congenital disorder of deglycosylation.

PURPOSE: The cytosolic enzyme N-glycanase 1, encoded by NGLY1, catalyzes cleavage of the ß-aspartyl glycosylamine bond of N-linked glycoproteins, releasing intact N-glycans from proteins bound for degradation. In this study, we describe the clinical spectrum of NGLY1 deficiency (NGLY1-CDDG). METHODS: Prospective natural history protocol. RESULTS: In 12 individuals ages 2 to 21 years with confirmed, biallelic, pathogenic NGLY1 mutations, we identified previously unreported clinical features, including optic atrophy and retinal pigmentary changes/cone dystrophy, delayed bone age, joint hypermobility, and lower than predicted resting energy expenditure. Novel laboratory findings include low cerebral spinal fluid (CSF) total protein and albumin and unusually high antibody titers toward rubella and/or rubeola following vaccination. We also confirmed and further quantified previously reported findings noting that decreased tear production, transient transaminitis, small feet, a complex hyperkinetic movement disorder, and varying degrees of global developmental delay with relatively preserved socialization are the most consistent features. CONCLUSION: Our prospective phenotyping expands the clinical spectrum of NGLY1-CDDG, offers prognostic information, and provides baseline data for evaluating therapeutic interventions.Genet Med 19 2, 160-168.

A Syndromic Neurodevelopmental Disorder Caused by De Novo Variants in EBF3.

Early B cell factor 3 (EBF3) is a member of the highly evolutionarily conserved Collier/Olf/EBF (COE) family of transcription factors. Prior studies on invertebrate and vertebrate animals have shown that EBF3 homologs are essential for survival and that loss-of-function mutations are associated with a range of nervous system developmental defects, including perturbation of neuronal development and migration. Interestingly, aristaless-related homeobox (ARX), a homeobox-containing transcription factor critical for the regulation of nervous system development, transcriptionally represses EBF3 expression. However, human neurodevelopmental disorders related to EBF3 have not been reported. Here, we describe three individuals who are affected by global developmental delay, intellectual disability, and expressive speech disorder and carry de novo variants in EBF3. Associated features seen in these individuals include congenital hypotonia, structural CNS malformations, ataxia, and genitourinary abnormalities. The de novo variants affect a single conserved residue in a zinc finger motif crucial for DNA binding and are deleterious in a fly model. Our findings indicate that mutations in EBF3 cause a genetic neurodevelopmental syndrome and suggest that loss of EBF3 function might mediate a subset of neurologic phenotypes shared by ARX-related disorders, including intellectual disability, abnormal genitalia, and structural CNS malformations.

Mitotic Intragenic Recombination: A Mechanism of Survival for Several Congenital Disorders of Glycosylation.

Congenital disorders of glycosylation (CDGs) are disorders of abnormal protein glycosylation that affect multiple organ systems. Because most CDGs have been described in only a few individuals, our understanding of the associated phenotypes and the mechanisms of individual survival are limited. In the process of studying two siblings, aged 6 and 11 years, with MOGS-CDG and biallelic MOGS (mannosyl-oligosaccharide glucosidase) mutations (GenBank: NM_006302.2; c.[65C>A; 329G>A] p.[Ala22Glu; Arg110His]; c.[370C>T] p.[Gln124(∗)]), we noted that their survival was much longer than the previous report of MOGS-CDG, in a child who died at 74 days of age. Upon mutation analysis, we detected multiple MOGS genotypes including wild-type alleles in their cultured fibroblast and peripheral blood DNA. Further analysis of DNA from cultured fibroblasts of six individuals with compound heterozygous mutations of PMM2 (PMM2-CDG), MPI (MPI-CDG), ALG3 (ALG3-CDG), ALG12 (ALG12-CDG), DPAGT1 (DPAGT1-CDG), and ALG1 (ALG1-CDG) also identified multiple genotypes including wild-type alleles for each. Droplet digital PCR showed a ratio of nearly 1:1 wild-type to mutant alleles for most, but not all, mutations. This suggests that mitotic recombination contributes to the survival and the variable expressivity of individuals with compound heterozygous CDGs. This also provides an explanation for prior observations of a reduced frequency of homozygous mutations and might contribute to increased levels of residual enzyme activity in cultured fibroblasts of individuals with MPI- and PMM2-CDGs.

Disruption of Golgi morphology and altered protein glycosylation in PLA2G6-associated neurodegeneration.

BACKGROUND: Mutations in PLA2G6, which encodes the calcium-independent phospholipase A2 group VI, cause neurodegeneration and diffuse cortical Lewy body formation by a yet undefined mechanism. We assessed whether altered protein glycosylation due to abnormal Golgi morphology might be a factor in the pathology of this disease. METHODS: Three patients presented with PLA2G6-associated neurodegeneration (PLAN); two had infantile neuroaxonal dystrophy (INAD) and one had adult-onset dystonia-parkinsonism. We analysed protein N-linked and O-linked glycosylation in cerebrospinal fluid, plasma, urine, and cultured skin fibroblasts using high performance liquid chromatography (HPLC) and matrix-assisted laser desorption ionization--time of flight/mass spectrometry (MALDI-TOF/MS). We also assessed sialylation and Golgi morphology in cultured fibroblasts by immunofluorescence and performed rescue experiments using a lentiviral vector. RESULTS: The patients with INAD had PLA2G6 mutations NM_003560.2: c.[950G>T];[426-1077dup] and c.[1799G>A];[2221C>T] and the patient with dystonia-parkinsonism had PLA2G6 mutations NM_003560.2: c.[609G>A];[2222G>A]. All three patients had altered Golgi morphology and abnormalities of protein O-linked glycosylation and sialylation in cultured fibroblasts that were rescued by lentiviral overexpression of wild type PLA2G6. CONCLUSIONS: Our findings add altered Golgi morphology, O-linked glycosylation and sialylation defects to the phenotypical spectrum of PLAN; these pathways are essential for correct processing and distribution of proteins. Lewy body and Tau pathology, two neuropathological features of PLAN, could emerge from these defects. Therefore, Golgi morphology, O-linked glycosylation and sialylation may play a role in the pathogenesis of PLAN and perhaps other neurodegenerative disorders.

Expanding the clinical and molecular characteristics of PIGT-CDG, a disorder of glycosylphosphatidylinositol anchors.

PIGT-CDG, an autosomal recessive syndromic intellectual disability disorder of glycosylphosphatidylinositol (GPI) anchors, was recently described in two independent kindreds [Multiple Congenital Anomalies-Hypotonia-Seizures Syndrome 3 (OMIM, #615398)]. PIGT encodes phosphatidylinositol-glycan biosynthesis class T, a subunit of the heteropentameric transamidase complex that facilitates the transfer of GPI to proteins. GPI facilitates attachment (anchoring) of proteins to cell membranes. We describe, at ages 7 and 6 years, two children of non-consanguineous parents; they had hypotonia, severe global developmental delay, and intractable seizures along with endocrine, ophthalmologic, skeletal, hearing, and cardiac anomalies. Exome sequencing revealed that both siblings had compound heterozygous variants in PIGT (NM_015937.5), i.e., c.918dupC, a novel duplication leading to a frameshift, and c.1342C > T encoding a previously described missense variant. Flow cytometry studies showed decreased surface expression of GPI-anchored proteins on granulocytes, consistent with findings in previous cases. These siblings further delineate the clinical spectrum of PIGT-CDG, reemphasize the neuro-ophthalmologic presentation, clarify the endocrine features, and add hypermobility, low CSF albumin quotient, and hearing loss to the phenotypic spectrum. Our results emphasize that GPI anchor-related congenital disorders of glycosylation (CDGs) should be considered in subjects with early onset severe seizure disorders and dysmorphic facial features, even in the presence of a normal carbohydrate-deficient transferrin pattern and N-glycan profiling. Currently available screening for CDGs will not reliably detect this family of disorders, and our case reaffirms that the use of flow cytometry and genetic testing is essential for diagnosis in this group of disorders.

Nutrition before, during, and after surgery increases the arginine:asymmetric dimethylarginine ratio and relates to improved myocardial glucose metabolism: a randomized controlled trial.

BACKGROUND: Nitric oxide (NO) is essential for the optimal perfusion of the heart and its vasculature. NO may be insufficient in surgical patients because its precursor arginine is decreased, and the inhibitor of NO synthesis asymmetric dimethylarginine (ADMA) is increased. Besides arginine, the presence of other amino acids essential for the proper metabolism of cardiac cells may be decreased too. Supplementation of these amino acids with enteral and parenteral nutrition before, during, and after surgery may augment the myocardial and plasma arginine:ADMA ratio and availability of amino acids. Myocardial glucose metabolism and nutritional conditioning may result in a reduction of cardiac injury and support rapid recovery after major surgery. OBJECTIVE: We investigated the effect of nutrition before, during, and after surgery on amino acids and the myocardial arginine:ADMA ratio and its relation to myocardial glucose metabolism. DESIGN: In this trial, 33 patients who were undergoing off-pump coronary artery bypass grafting (CABG) were randomly assigned between enteral, parenteral, or no nutrition (control) from 2 d before, during, and until 2 d after surgery. Both enteral and parenteral solutions were prepared with commercially available products and included proteins or amino acids, glucose, vitamins, and minerals. Concentrations of amino acids including ADMA were analyzed in myocardial tissue and plasma samples. ¹8F-fluorodeoxyglucose positron emission tomography was performed before and after surgery to assess myocardial glucose metabolism. RESULTS: The myocardial arginine:ADMA ratio increased during surgery and was significantly higher in the enteral and parenteral groups than in the control group [median (IQR): 115.0 (98.0-142.2) (P = 0.012), 116.9 (100.3-135.3) (P = 0.004), and 93.3 (82.7-101.1), respectively]. Furthermore, the change in the preoperative to postoperative plasma arginine:ADMA ratio correlated with the change in myocardial glucose metabolism in positron emission tomography (r = 0.427, P = 0.033). CONCLUSION: Enteral or parenteral nutrition before, during, and after CABG may positively influence myocardial glucose metabolism by increasing the plasma and myocardial arginine:ADMA ratio.

Protein arginine hypomethylation in a mouse model of cystathionine ß-synthase deficiency.

Accumulation of the homocysteine (Hcy) precursor S-adenosylhomocysteine (AdoHcy) may cause cellular hypomethylation in the setting of hyperhomocysteinemia because of cystathionine ß-synthase (CBS) deficiency, an inborn error of metabolism. To test this hypothesis, DNA and protein arginine methylation status were assessed in liver, brain, heart, and kidney obtained from a previously described mouse model of CBS deficiency. Metabolite levels in tissues and serum were determined by high-performance liquid chromatography or liquid chromatography-electrospray ionization-tandem mass spectrometry. Global DNA and protein arginine methylation status were evaluated as the contents of 5-methyldeoxycytidine in DNA and of methylarginines in proteins, respectively. In addition, histone arginine methylation was assessed by Western blotting. CBS-deficient mice exhibited increased (>6-fold) Hcy and AdoHcy levels in all tissues examined compared with control levels. In addition, global DNA methylation status was not affected, but global protein arginine methylation status was decreased (10-35%) in liver and brain. Moreover, asymmetric dimethylation of arginine 3 on histone H4 (H4R3me2a) content was markedly decreased in liver, and no differences were observed for the other histone arginine methylation marks examined. Our results show that CBS-deficient mice present severe accumulation of tissue Hcy and AdoHcy, protein arginine hypomethylation in liver and brain, and decreased H4R3me2a content in liver. Therefore, protein arginine hypomethylation arises as a potential player in the pathophysiology of CBS deficiency.

Plasma concentrations of arginine and asymmetric dimethylarginine do not reflect their intracellular concentrations in peripheral blood mononuclear cells.

OBJECTIVE: Production of nitric oxide (NO) from arginine is inhibited by endogenously produced monomethylarginine (MMA) and asymmetric dimethylarginine (ADMA). Elevated levels of ADMA, by limiting NO production, may lead to endothelial dysfunction and cardiovascular disease. Symmetric dimethylarginine (SDMA) and the arginine homolog homoarginine have also been associated with cardiovascular disease. Although NO synthesis, as well as generation of MMA, ADMA, SDMA and homoarginine, occurs intracellularly, these biomarkers are usually measured in plasma. Despite extensive transmembrane transport, it is not clear whether plasma levels of these biomarkers are a valid proxy for their intracellular levels in the cardiovascular system. Since it is difficult to obtain vascular tissue from healthy humans, we explored the relations between concentrations of these biomarkers in plasma and intracellular concentrations in peripheral blood mononuclear cells (PBMC). METHODS: In PBMC and plasma of 27 healthy subjects, concentrations of arginine, MMA, ADMA, SDMA, and homoarginine were determined using stable isotope dilution liquid chromatography tandem mass spectrometry. RESULTS: In PBMC, significant positive correlations were observed among arginine and its methylated forms (ρ = 0.43 to 0.81) and these correlations were slightly less pronounced in plasma. Homoarginine was not significantly correlated with (methylated) arginine in either PBMC or plasma. Plasma concentrations of arginine and its methylated forms showed non-significant inverse associations with their respective intracellular concentrations in PBMC and only for homoarginine was a weak positive association observed (ρ = 0.37). CONCLUSION: In healthy individuals, plasma levels of arginine, MMA, ADMA, and SDMA poorly reflect their intracellular levels in PBMC.