Eva Morava

Intellectual disability and bleeding diathesis due to deficient CMP–sialic acid transport

Objective: To identify the underlying genetic defect in a patient with intellectual disability, seizures, ataxia, macrothrombocytopenia, renal and cardiac involvement, and abnormal protein glycosylation. Methods: Genetic studies involved homozygosity mapping by 250K single nucleotide polymorphism array and SLC35A1 sequencing. Functional studies included biochemical assays for N-glycosylation and mucin-type O-glycosylation and SLC35A1-encoded cytidine 5′-monophosphosialic acid (CMP–sialic acid) transport after heterologous expression in yeast. Results: We performed biochemical analysis and found combined N- and O-glycosylation abnormalities and specific reduction in sialylation in this patient. Homozygosity mapping revealed homozygosity for the CMP–sialic acid transporter SLC35A1. Mutation analysis identified a homozygous c.303G>C (p.Gln101His) missense mutation that was heterozygous in both parents. Functional analysis of mutant SLC35A1 showed normal Golgi localization but 50% reduction in transport activity of CMP–sialic acid in vitro. Conclusion: We confirm an autosomal recessive, generalized sialylation defect due to mutations in SLC35A1. The primary neurologic presentation consisting of ataxia, intellectual disability, and seizures, in combination with bleeding diathesis and proteinuria, is discriminative from a previous case described with deficient sialic acid transporter. Our study underlines the importance of sialylation for normal CNS development and regular organ function.

Oral D-galactose supplementation in PGM1-CDG

PurposePhosphoglucomutase-1 deficiency is a subtype of congenital disorders of glycosylation (PGM1-CDG). Previous casereports in PGM1-CDG patients receiving oral D-galactose (D-gal) showed clinical improvement. So far no systematic in vitro and clinical studies have assessed safety and benefits of D-gal supplementation. In a prospective pilot study, we evaluated the effects of oral D-gal in nine patients.MethodsD-gal supplementation was increased to 1.5u2009g/kg/day (maximum 50u2009g/day) in three increments over 18 weeks. Laboratory studies were performed before and during treatment to monitor safety and effect on serum transferrin-glycosylation, coagulation, and liver and endocrine function. Additionally, the effect of D-gal on cellular glycosylation was characterized in vitro.ResultsEight patients were compliant with D-gal supplementation. No adverse effects were reported. Abnormal baseline results (alanine transaminase, aspartate transaminase, activated partial thromboplastin time) improved or normalized already using 1u2009g/kg/day D-gal. Antithrombin-III levels and transferrin-glycosylation showed significant improvement, and increase in galactosylation and whole glycan content. In vitro studies before treatment showed N-glycan hyposialylation, altered O-linked glycans, abnormal lipid-linked oligosaccharide profile, and abnormal nucleotide sugars in patient fibroblasts. Most cellular abnormalities improved or normalized following D-gal treatment. D-gal increased both UDP-Glc and UDP-Gal levels and improved lipid-linked oligosaccharide fractions in concert with improved glycosylation in PGM1-CDG.ConclusionOral D-gal supplementation is a safe and effective treatment for PGM1-CDG in this pilot study. Transferrin glycosylation and ATIII levels were useful trial end points. Larger, longer-duration trials are ongoing.

Bi-allelic Mutations in the Mitochondrial Ribosomal Protein MRPS2 Cause Sensorineural Hearing Loss, Hypoglycemia, and Multiple OXPHOS Complex Deficiencies

Biogenesis of the mitochondrial oxidative phosphorylation system, which produces the bulk of ATP for almost all eukaryotic cells, depends on the translation of 13 mtDNA-encoded polypeptides by mitochondria-specific ribosomes in the mitochondrial matrix. These mitoribosomes are dual-origin ribonucleoprotein complexes, which contain mtDNA-encoded rRNAs and tRNAs and ∼80 nucleus-encoded proteins. An increasing number of gene mutations that impair mitoribosomal function and result in multiple OXPHOS deficiencies are being linked to human mitochondrial diseases. Using exome sequencing in two unrelated subjects presenting with sensorineural hearing impairment, mild developmental delay, hypoglycemia, and a combined OXPHOS deficiency, we identified mutations in the gene encoding the mitochondrial ribosomal protein S2, which has not previously been implicated in disease. Characterization of subjects fibroblasts revealed a decrease in the steady-state amounts of mutant MRPS2, and this decrease was shown by complexome profiling to prevent the assembly of the small mitoribosomal subunit. In turn, mitochondrial translation was inhibited, resulting in a combined OXPHOS deficiency detectable in subjects muscle and liver biopsies as well as in cultured skin fibroblasts. Reintroduction of wild-type MRPS2 restored mitochondrial translation and OXPHOS assembly. The combination of lactic acidemia, hypoglycemia, and sensorineural hearing loss, especially in the presence of a combined OXPHOS deficiency, should raise suspicion for a ribosomal-subunit-related mitochondrial defect, and clinical recognition could allow for a targeted diagnostic approach. The identification of MRPS2 as an additional gene related to mitochondrial disease further expands the genetic and phenotypic spectra of OXPHOS deficiencies caused by impaired mitochondrial translation.

Intact transferrin and total plasma glycoprofiling for diagnosis and therapy monitoring in phosphoglucomutase-I deficiency

Phosphoglucomutase 1 (PGM1) deficiency results in a mixed phenotype of a Glycogen Storage Disorder and a Congenital Disorder of Glycosylation (CDG). Screening for abnormal glycosylation has identified more than 40 patients, manifesting with a broad clinical and biochemical spectrum which complicates diagnosis. Together with the availability of D‐galactose as dietary therapy, there is an urgent need for specific glycomarkers for early diagnosis and treatment monitoring. We performed glycomics profiling by high‐resolution QTOF mass spectrometry in a series of 19 PGM1‐CDG patients, covering a broad range of biochemical and clinical severity. Bioinformatics and statistical analysis were used to select glycomarkers for diagnostics and define glycan‐indexes for treatment monitoring. Using 3 transferrin glycobiomarkers, all PGM1‐CDG patients were diagnosed with 100% specificity and sensitivity. Total plasma glycoprofiling showed an increase in high mannose glycans and fucosylation, while global galactosylation and sialylation were severely decreased. For treatment monitoring, we defined 3 glycan‐indexes, reflecting normal glycosylation, a lack of complete glycans (LOCGI) and of galactose residues (LOGI). These indexes showed improved glycosylation upon D‐galactose treatment with a fast and near‐normalization of the galactose index (LOGI) in 6 out of 8 patients and a slower normalization of the LOCGI in all patients. Total plasma glycoprofiling showed improvement of the global high mannose glycans, fucosylation, sialylation, and galactosylation status on D‐galactose treatment. Our study indicates specific glycomarkers for diagnosis of mildly and severely affected PGM1‐CDG patients, and to monitor the glycan‐specific effects of D‐galactose therapy.

Secondary Hemophagocytic Syndrome Associated with COG6 Gene Defect: Report and Review

Hemophagocytic lymphohistiocytosis (HLH) is a rare but potentially fatal disease that is characterized by proliferation and infiltration of hyperactivated macrophages and T-lymphocytes. Clinically, it is characterized by prolonged fever, hepatosplenomegaly, hypertriglyceridemia, hypofibrinogenemia, pancytopenia, and hemophagocytosis in the bone marrow, spleen, or lymph nodes. It can be classified as primary if it is due to a genetic defect, or secondary if it is due to a different etiology such as severe infection, immune deficiency syndrome, rheumatological disorder, malignancy, and inborn errors of metabolism such as galactosemia, multiple sulfatase deficiency, lysinuric protein intolerance, Gaucher disease, Niemann-Pick disease, Wolman disease, propionic acidemia, methylmalonic acidemia, biotinidase deficiency, cobalamin C defect, galactosialidosis, Pearson syndrome, and long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency. For the first time in the literature, we report on a 5-year-old girl diagnosed with a Component of Oligomeric Golgi Complex 6 (COG6) gene defect complicated by HLH. Finally, we review the literature on inborn errors of metabolism associated with HLH and compare the previously reported patients of COG6 gene defect with our patient.

Central nervous involvement is common in PGM1-CDG

PGM1, the enzyme responsible for the reversible inter-conversion of glucose-1-P and glucose-6-P, is also involved in glycosylation, leading to a wide range of clinical manifestations, such as congenital malformations, hypoglycemia, hormonal dysregulation, myopathy, hepatopathy, and cardiomyopathy. So far, PGM1 deficiency has not been associated with central nervous system involvement or intellectual disability. Seizures and neurologic involvement in PGM1-CDG were thought to be a consequence of hypoglycemia. We reviewed all reported PGM1 deficient patients for the presence of the central nervous system involvement, their treatment and disease history. We detected 17 patients out of the 41 reported PGM1-CDG cases with significant neurologic involvement. Several of these patients had no severe hypoglycemic episodes, or were adequately treated for hypoglycemia with no recurrent episodes of low blood sugars, while one patient had no reported hypoglycemic episodes. We suggest that neurological symptoms are frequent in PGM1-CDG and could present even in the absence of hypoglycemia. The central nervous system should be assessed early on during the diagnostic process to optimize outcome in patients with PGM1-CDG.

A new opportunity: metabolism and neuropsychiatric disorders

Neuropsychiatric disorders are associated with significant negative personal and social impacts. Current efforts to treat neuropsychiatric disorders often achieve suboptimal results, leading to recurrent and chronic disease. A remarkable effort has been invested in understanding the genetics and pathophysiology of pediatric and adult neuropsychiatric disorders. Yet we have not made enough progress to offer causal explanation for disturbed behavior, or choosing a treatment based on pathophysiology. Our present knowledge is also incomplete in predicting who will (Bsusceptible individual^) and who will not (Bresilient individual^) develop a neuropsychiatric disorder. There is a great need to scale up research and also to explore novel concepts to unravel alterations at system level, contributing to disease etiology. Such system-level approach could be Bimpaired metabolism^ in neuropsychiatry. In this special issue of Journal of InheritedMetabolic Disease, we have an excellent collection of original articles as well as comprehensive reviews on this matter. Behavior abnormalities and psychological symptoms are well-known symptoms of many inborn errors of metabolism. Classic metabolic disorders like attenuated forms of urea cycle disorders, MSUD, or propionic acidemia; abnormal synthesis of complex molecules like CDG or cerebrotendinous xantomatosis; porphyria; or storage disorders like NiemannPick C disease could all present as psychopathology, even before the classic symptoms of the disease emerge. Disorders of energy metabolism are rather unique from this aspect. Some billion years ago, one of our single-celled ancestors engulfed a unicellular prokaryote (Roger et al. 2017). These cells continued to evolve together and the endocytosed organism evolved what we know now as mitochondrion.Mitochondria are dynamic organelles and essential components of all eucaryal cells. Mitochondria perform numerous biological tasks and interact with virtually all cellular metabolic processes (Herst et al. 2017). Neuronal functions are especially dependent on mitochondria which supply our neurons with energy in the form of ATP (Roger et al. 2017). Therefore, a mitochondrial etiology of neuropsychiatric diseases is very likely (Kozicz et al. 2018; Pei and Wallace 2018). Specifically, a variety of neuropsychopathologies, including major depressive disorder, post-traumatic stress disorder, autism, and bipolar disorder as well as Parkinson’s and Alzheimer’s diseases, have been linked to genetic or acquired deficits in mitochondrial function (DiMauro and Schon 2008; Manji et al. 2012; Morava and Kozicz 2013; Srivastava 2017; Kozicz et al. 2018; Pei and Wallace 2018). In recent years, an increasing body of evidence— witnessed by the selection of articles and reviews in this special issue too—suggests increased vulnerability to neuropsychopathologies. For example, 50% of patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) present with comorbid major depressive disorder (Anglin et al. 2012). Autism spectrum disorders are frequent in patients with propionic acidemia, especially with chronic amino acid imbalance and lactic acidemia (Al-Owain et al. 2013; Ghaziuddin and Al-Owain 2013). Long-term outcome in MSUD, especially after dietary over-restriction, has been associated with amino acid imbalance and depression (Strauss et al. 1993). Attenuated forms of ornithine transcarbamylase deficiency with mild chronic hyperammonemia show a broad variety of psychopathology (Waisbren et al. 2016). Yet, not all patients with inborn errors of metabolism present with psychopathologies, so it is likely that perturbations in cellular (energy) metabolism are important risk factors and contribute to a certain percentage of explained * Tamas Kozicz Kozicz.tamas@mayo.edu

Long-term follow-up in PMM2-CDG: are we ready to start treatment trials?

PurposePMM2-CDG is the most common congenital disorder of glycosylation (CDG), which presents with either a neurologic or multisystem phenotype. Little is known about the longitudinal evolution.MethodsWe performed data analysis on PMM2-CDG patients’ clinical features according to the Nijmegen CDG severity score and laboratory data. Seventy-five patients (28 males) were followed up from 11.0u2009±u20096.91 years for an average of 7.4u2009±u20094.5 years.ResultsOn a group level, there was no significant evolution in overall clinical severity. There was some improvement in mobility and communication, liver and endocrine function, and strabismus and eye movements. Educational achievement and thyroid function worsened in some patients. Overall, the current clinical function, the system-specific involvement, and the current clinical assessment remained unchanged.On follow-up there was improvement of biochemical variables with (near) normalization of activated partial thromboplastin time (aPTT), factor XI, protein C, antithrombin, thyroid stimulating hormone, and liver transaminases.ConclusionPMM2-CDG patients show a spontaneous biochemical improvement and stable clinical course based on the Nijmegen CDG severity score. This information is crucial for the definition of endpoints in clinical trials.