Abnormal Transferrin Research Articles

Epidemiology and Prevalence of Patients with Congenital Disorders of Glycosylation in Malaysia

Congenital disorders of glycosylation (CDG) are rarely, inherited metabolic diseases in which the glycosylation process is severely impaired. The prevalence has not been well determined and the aims of this study were to describe the epidemiology and calculate the birth prevalence of CDG in the Malaysian population. From 2018 to 2022, 548 patients were suspected with CDG. Sample were collected and analysed using isoelectric focusing (IEF) and capillary zone electrophoresis (CZE) methods. Qualitative measurement of sialo pattern was determined to categorised CDG Type I, II and abnormal transferrin pattern. Transferrin level was quantitated using automated BN ProSpec® System as well as demographic and clinical features were documented. The distribution of CDG was 0.4% and 2.9% was diagnosed as abnormal transferrin types. The prevalence of CDG among Malaysian was 0.22 per 100,000 live births and the combined prevalence of abnormal pattern was 0.85 per 100,000 live births. Positive cases were found in infants of Malay ethnicity. Overall, the prevalence of CDG in Malaysia was low and may be underestimated yet consistent with other reported in other countries.

Active site variants in STT3A cause a dominant type I congenital disorder of glycosylation with neuromusculoskeletal findings

Congenital disorders of glycosylation (CDGs) form a group of rare diseases characterized by hypoglycosylation. We here report the identification of 16 individuals from nine families who have either inherited or de novo heterozygous missense variants in STT3A, leading to an autosomal-dominant CDG. STT3A encodes the catalytic subunit of the STT3A-containing oligosaccharyltransferase (OST) complex, essential for protein N-glycosylation. Affected individuals presented with variable skeletal anomalies, short stature, macrocephaly, and dysmorphic features; half had intellectual disability. Additional features included increased muscle tone and muscle cramps. Modeling of the variants in the 3D structure of the OST complex indicated that all variants are located in the catalytic site of STT3A, suggesting a direct mechanistic link to the transfer of oligosaccharides onto nascent glycoproteins. Indeed, expression of STT3A at mRNA and steady-state protein level in fibroblasts was normal, while glycosylation was abnormal. In S.cerevisiae, expression of STT3 containing variants homologous to those in affected individuals induced defective glycosylation of carboxypeptidase Y in a wild-type yeast strain and expression of the same mutants in the STT3 hypomorphic stt3-7 yeast strain worsened the already observed glycosylation defect. These data support a dominant pathomechanism underlying the glycosylation defect. Recessive mutations in STT3A have previously been described to lead to a CDG. We present here a dominant form of STT3A-CDG that, because of the presence of abnormal transferrin glycoforms, is unusual among dominant type I CDGs.

Transferrin Isoforms, Old but New Biomarkers in Hereditary Fructose Intolerance.

Hereditary Fructose Intolerance (HFI) is an autosomal recessive inborn error of metabolism characterised by the deficiency of the hepatic enzyme aldolase B. Its treatment consists in adopting a fructose-, sucrose-, and sorbitol (FSS)-restrictive diet for life. Untreated HFI patients present an abnormal transferrin (Tf) glycosylation pattern due to the inhibition of mannose-6-phosphate isomerase by fructose-1-phosphate. Hence, elevated serum carbohydrate-deficient Tf (CDT) may allow the prompt detection of HFI. The CDT values improve when an FSS-restrictive diet is followed; however, previous data on CDT and fructose intake correlation are inconsistent. Therefore, we examined the complete serum sialoTf profile and correlated it with FSS dietary intake and with hepatic parameters in a cohort of paediatric and adult fructosemic patients. To do so, the profiles of serum sialoTf from genetically diagnosed HFI patients on an FSS-restricted diet (n = 37) and their age-, sex- and body mass index-paired controls (n = 32) were analysed by capillary zone electrophoresis. We found that in HFI patients, asialoTf correlated with dietary intake of sucrose (R = 0.575, p < 0.001) and FSS (R = 0.475, p = 0.008), and that pentasialoTf+hexasialoTf negatively correlated with dietary intake of fructose (R = −0.386, p = 0.024) and FSS (R = −0.400, p = 0.019). In addition, the tetrasialoTf/disialoTf ratio truthfully differentiated treated HFI patients from healthy controls, with an area under the ROC curve (AUROC) of 0.97, 92% sensitivity, 94% specificity and 93% accuracy.

Routine Preoperative Nutritional Screening in All Primary Total Joint Arthroplasty Patients Has Little Utility

BackgroundNutritional optimization before total joint arthroplasty (TJA) may improve patient outcomes and decrease costs. However, the utility of serologic laboratory markers, including albumin, transferrin, and total lymphocyte count (TLC), as primary indicators of nutrition is unclear. We analyzed the prevalence of abnormal nutritional values before TJA and identified factors associated with them. MethodsWe retrospectively reviewed 819 primary cases of TJA performed at 1 institution from January to December 2018. Patient demographic characteristics were assessed for associations with abnormal preoperative nutritional values (albumin <3.5 g/dL, transferrin <200 mg/dL, and TLC <1.5 cells/μL3). Associations of comorbidities, American Society of Anesthesiologists Physical Status classification, and age-adjusted Charlson Comorbidity Index (CCI) with abnormal values were assessed with logistic regression. ResultsValues were abnormal for albumin in 21 cases (2.6%), transferrin in 26 cases (5.6%), and TLC in 185 cases (25%). Thirteen cases (1.7%) had abnormal values for 2 markers. Age was associated with abnormal albumin and TLC, and race with abnormal transferrin. Congestive heart failure, chronic kidney disease, pancreatic insufficiency, gastroesophageal reflux disease, osteoporosis, dementia, and CCI were associated with abnormal albumin; Parkinson disease and American Society of Anesthesiologists Physical Status with abnormal transferrin; and dementia, body mass index, cancer history, and CCI with abnormal TLC. ConclusionWe report low prevalence of and a low concordance rate among abnormal nutritional values before primary TJA. Our results suggest that routine testing of all healthy patients is not warranted before TJA.

Hypomorphic CAMKK2 in EA.hy926 endothelial cells causes abnormal transferrin trafficking, iron homeostasis and glucose metabolism

We recently reported that loss of calcium/calmodulin-dependent protein kinase kinase-2 (CAMKK2), a serine/threonine kinase activated by intracellular calcium, in mice leads to tissue-specific aberrant turnover of transferrin (TF), a receptor-mediated iron-transporter that supplies iron to tissues. Iron dyshomeostasis is associated with the pathogenesis of several diseases, making TF transport relevant to health. In this study, we used hemizygous CAMKK2 hypomorphic human endothelial cell (EA.hy926) clones to demonstrate that cells with reduced CAMKK2 exhibit increased TF uptake and transcytosis, and decreased intracellular trafficking to subcellular organelles compared to wild-type. The abnormal TF trafficking in CAMKK2 hypomorphic cells correlated with a reduction in intracellular iron content and defective glucose metabolism including glycolysis and mitochondrial respiration. CAMKK2 deficiency also caused reduction in GAPDH and VDAC1 protein level which correlated to defective bioenergetics function. These findings have identified a novel mechanistic link between abnormal calcium signaling, iron dyshomeostasis and metabolic dysfunction involving CAMKK2.

CAMKK2-CAMK4 signaling regulates transferrin trafficking, turnover, and iron\xa0homeostasis

BackgroundCirculatory iron is a hazardous biometal. Therefore, iron is transported in a redox-safe state by a serum glycoprotein - transferrin (TF). Different organs acquire iron from the systemic circulation through a tightly regulated mechanism at the blood-tissue interface which involves receptor-mediated internalization of TF. Thus, abnormal TF trafficking may lead to iron dyshomeostasis associated with several diseases including neurodegeneration. Iron -induced toxicity can cause neuronal damage to iron-sensitive brain regions. Recently, it was discovered that CAMKK2, a calcium (Ca2+)/calmodulin-activated kinase, controls receptor-mediated TF trafficking in mouse tissues, specifically in the brain. The biological function of CAMKK2 is mediated through multiple downstream effectors. Both CAMKK2 and one of its downstream kinase, CAMK4, exhibit overlapping expression in mouse brain. The role of CAMK4 in vesicular transport has been reported and loss of CAMKK2 or CAMK4 leads to cognitive defects in mouse. Therefore, it was hypothesized that CAMKK2-CAMK4 signaling regulates receptor-mediated TF trafficking and iron homeostasis which may be responsible for the neuronal malfunction observed in CAMKK2- or CAMK4-deficient mice.MethodsCAMK4−/− mouse was used to study tissue-specific turnover of TF, TF-receptor (TFRC) and iron. CRISPR/Cas9-based CAMKK2 and/or CAMK4 deleted human embryonic kidney-derived HEK293 cell clones were used to study the molecular defects in receptor-mediated TF trafficking. Further, a “zero functional G protein” condition in HEK293 cell was exploited to study CAMKK2-CAMK4 signaling-mediated regulation of intracellular Ca2+ homeostasis which was linked to calcium signaling during TF trafficking.ResultsLoss of CAMK4 leads to abnormal post-translational modifications (PTMs) and turnover of TF in mouse cerebellum and liver which was associated with iron dyshomeostasis in these tissues. The HEK293 cell-based study revealed that the absence of CAMKK2-CAMK4 signaling altered intracellular Ca2+ homeostasis and lead to abnormal calcium signaling during TF trafficking. Also, CAMKK2-CAMK4 signaling deficiency affected the molecular interaction of TF and TF-receptor-associated protein complexes which indicated a potential failure in the recruitment of interacting proteins due to differential PTMs in TF.ConclusionOverall, this study established a novel mechanistic link between intracellular Ca2+ level, receptor-mediated TF trafficking, and iron homeostasis, all regulated by CAMKK2-CAMK4 signaling.96jS1k-UhvBwj8b5MHadpoVideo Graphical abstract

Study of Glycation of Transferrin and its Effect on Biomarkers of Iron Status in Uncontrolled Diabetes Mellitus Patients

Introduction: Diabetes Mellitus (DM) is a metabolic condition linked by the inability to produce enough insulin and/or to respond to insulin. This can lead to a number of acute and chronic health problems. In erythrocytes, transferrin is the main source of iron. Alterations in transferrin glycation affect transferrin saturation because the affinity of transferrin for Fe3+ is extremely high but it decreases progressively with increasing glycation. Aim: To investigate the influence of uncontrolled diabetes on transferrin glycation and iron metabolism. Materials and Methods: A total of 136 samples from 3 groups of HbA1c levels (&lt;6.0% non-diabetic, 6.4-8% diabetic, &gt;8.0%-uncontrolled DM) were studied for the correlation pattern of iron with other variables. Chi square test and student’s t-test were performed to reveal the association between serum free iron levels and other variables with DM. Results: Serum iron has shown to be depleted significantly (p=0.02) along with percentage saturation (p=0.0006) with increase in diabetic severity. No significant differences were observed in serum ferritin in controlled DM and uncontrolled samples. Total Iron Binding Capacity (TIBC) was found to be significantly increased in uncontrolled DM samples (p=0.01). Abnormal transferrin was observed uncontrolled diabetes with subsequent depletion in transferrin, which in turn results in low serum iron, lower percentage saturation and high TIBC. Conclusion: Uncontrolled diabetes affects the glycation of transferrin also thus perturbating iron metabolism. The present study emphasises the need to monitor transferrin glycation status and iron deficiency anaemia in subjects with uncontrolled diabetes.

Activation of a cryptic splice site in the mitochondrial elongation factor GFM1 causes combined OXPHOS deficiency

We report the clinical, biochemical, and molecular findings in two brothers with encephalopathy and multi-systemic disease. Abnormal transferrin glycoforms were suggestive of a type I congenital disorder of glycosylation (CDG). While exome sequencing was negative for CDG related candidate genes, the testing revealed compound heterozygous mutations in the mitochondrial elongation factor G gene (GFM1). One of the mutations had been reported previously while the second, novel variant was found deep in intron 6, activating a cryptic splice site. Functional studies demonstrated decreased GFM1 protein levels, suggested disrupted assembly of mitochondrial complexes III and V and decreased activities of mitochondrial complexes I and IV, all indicating combined OXPHOS deficiency.

SLC39A8 Deficiency: A Disorder of Manganese Transport and Glycosylation

SLC39A8 is a membrane transporter responsible for manganese uptake into the cell. Via whole-exome sequencing, we studied a child that presented with cranial asymmetry, severe infantile spasms with hypsarrhythmia, and dysproportionate dwarfism. Analysis of transferrin glycosylation revealed severe dysglycosylation corresponding to a type II congenital disorder of glycosylation (CDG) and the blood manganese levels were below the detection limit. The variants c.112G>C (p.Gly38Arg) and c.1019T>A (p.Ile340Asn) were identified in SLC39A8. A second individual with the variants c.97G>A (p.Val33Met) and c.1004G>C (p.Ser335Thr) on the paternal allele and c.610G>T (p.Gly204Cys) on the maternal allele was identified among a group of unresolved case subjects with CDG. These data demonstrate that variants in SLC39A8 impair the function of manganese-dependent enzymes, most notably β-1,4-galactosyltransferase, a Golgi enzyme essential for biosynthesis of the carbohydrate part of glycoproteins. Impaired galactosylation leads to a severe disorder with deformed skull, severe seizures, short limbs, profound psychomotor retardation, and hearing loss. Oral galactose supplementation is a treatment option and results in complete normalization of glycosylation. SLC39A8 deficiency links a trace element deficiency with inherited glycosylation disorders.

Congenital disorders of glycosylation: new defects and still counting.

Almost 50 inborn errors of metabolism have been described due to congenital defects in N-linked glycosylation. These phenotypically diverse disorders typically present as clinical syndromes, affecting multiple systems including the central nervous system, muscle function, transport, regulation, immunity, endocrine system, and coagulation. An increasing number of disorders have been discovered using novel techniques that combine glycobiology with next-generation sequencing or use tandem mass spectrometry in combination with molecular gene-hunting techniques. The number of "classic" congenital disorders of glycosylation (CDGs) due to N-linked glycosylation defects is still rising. Eight novel CDGs affecting N-linked glycans were discovered in 2013 alone. Newly discovered genes teach us about the significance of glycosylation in cell-cell interaction, signaling, organ development, cell survival, and mosaicism, in addition to the consequences of abnormal glycosylation for muscle function. We have learned how important glycosylation is in posttranslational modification and how glycosylation defects can imitate recognizable, previously described phenotypes. In many CDG subtypes, patients unexpectedly presented with long-term survival, whereas some others presented with nonsyndromic intellectual disability. In this review, recently discovered N-linked CDGs are described, with a focus on clinical presentations and therapeutic ideas. A diagnostic approach in unsolved N-linked CDG cases with abnormal transferrin screening results is also suggested.

DDOST Mutations Identified by Whole-Exome Sequencing Are Implicated in Congenital Disorders of Glycosylation

Congenital disorders of glycosylation (CDG) are inherited autosomal-recessive diseases that impair N-glycosylation. Approximately 20% of patients do not survive beyond the age of 5 years old as a result of widespread organ dysfunction. Although most patients receive a CDG diagnosis based on abnormal glycosylation of transferrin, this test cannot provide a genetic diagnosis; indeed, many patients with abnormal transferrin do not have mutations in any known CDG genes. Here, we combined biochemical analysis with whole-exome sequencing (WES) to identify the genetic defect in an untyped CDG patient, and we found a 22 bp deletion and a missense mutation in DDOST, whose product is a component of the oligosaccharyltransferase complex that transfers the glycan chain from a lipid carrier to nascent proteins in the endoplasmic reticulum lumen. Biochemical analysis with three biomarkers revealed that N-glycosylation was decreased in the patient's fibroblasts. Complementation with wild-type-DDOST cDNA in patient fibroblasts restored glycosylation, indicating that the mutations were pathological. Our results highlight the power of combining WES and biochemical studies, including a glyco-complementation system, for identifying and confirming the defective gene in an untyped CDG patient. This approach will be very useful for uncovering other types of CDG as well.

How to find and diagnose a CDG due to defective N‐glycosylation

The group of Congenital Disorders of Glycosylation (CDG) is expanding rapidly since the first clinical description of the N-glycosylation defect PMM2-CDG (CDG-Ia) in 1980 (Jaeken et al. 1980). Since then, more than 50 defects have been identified in protein N-glycosylation (some of them also associated with an O-glycosylation defect), in protein O-glycosylation only and in lipid glycosylation (GPI anchor and glycosphingolipid synthesis). Here, we provide a simple approach to the clinical, biochemical and genetic diagnosis of CDG due to a N-glycosylation defect (including combined N- and O-glycosylation defects).

Secondary disorders of glycosylation in inborn errors of fructose metabolism

Adamowicz and colleagues raised the alert in 2007 about patients with atypical hereditary fructose intolerance (HFI) primarily misdiagnosed as CDG Ix. We describe a girl with neonatal hypertonia, facial trismus, absent swallowing and coughing reflexes, gastro-oesophageal reflux and sporadically elevated Krebs cycle metabolites and lactate. At 14 months microcephaly and hepatomegaly were noted, with hypertransaminasaemia but normal blood coagulation, glucose, phosphate, and absent urinary reducing substances. Neurological impairment persisted. Because of hepatic and neurological abnormalities with developmental delay, Tf IEF was performed and showed a severe type 1 pattern, resulting in a wrong diagnosis of CDG. Subsequently, an aversion to fruits suggested HFI, confirmed by the finding of ALDOB mutations (p.A150P/p.N335K). The girl improved with fructose-free diet, but liver cirrhosis led to hepatic transplantation. She is now 7 years old with good evolution; facial trismus and hypertonia reversed, but microcephaly persists. Transferrin MALDI-TOF MS characterization revealed underoccupation of glycosylation sites and glycan abnormalities, which reversed with dietary treatment. High maternal fructose concentrations might have caused neonatal abnormalities. Although in our patient's mother there is no fructose accumulation at present, it is possible that increased ingestion of fruits and vegetables during pregnancy, together with her heterozygosity, caused an accumulation of fructose that finally affected the fetus. We also describe slightly abnormal transferrin isoelectric focusing and MALDI-TOF MS patterns of intact transferrin and N-glycans in a fructose-1,6-bisphosphatase (FBP1)-deficient patient. While HFI is a well-known cause of secondary CDG, we found no reports of abnormal transferrin isoelectric focusing patterns in FBP1 deficiency and we introduce this condition as a possible secondary cause for altered transferrin isoelectric focusing.

Pericardial and abdominal fluid accumulation in Congenital Disorder of Glycosylation type Ia

The association of fetal hydrops with Congenital Disorders of Glycosylation (CDG) has been reported previously. Pericardial fluid accumulation and ascites were also observed in a few young patients with CDG type Ia. Here we describe the clinical and biochemical features in three children developing life-threatening extravascular fluid accumulation. All patients carried severe PMM2 mutations comparable to the earlier reported patients with fetal hydrops. One patient was successfully treated with a pericardial–pleural shunt placement. Pericardial fluid accumulation and generalized oedema resolved temporarily in the other two children on regular albumin infusions and the use of diuretics. Sequential abdominal punctures were unsuccessful in the treatment of the extensive ascites production. The use of non-steroid anti-inflammatory agents and the application of high dose steroids had no clinical effect. Severe extravascular fluid accumulation progressed to decompensation and death. Biochemical investigations of the abdominal fluid and pericardial fluid demonstrated a high extracellular protein concentration, increased cytokine concentrations and an abnormal transferrin isoelectric focusing pattern characteristic of CDG type I. Our results are consistent with a local activation of the cytokine pathways and subsequent protein transport through the endothelial surface to the extravascular space. Normal glycosylation of cell surface proteins is essential for the normal fluid balance and protein transport through the pericardial and peritoneal membrane. Future therapeutic efforts should be directed to inhibit the abnormal immune response and excessive protein transport in this life-threatening complication of CDG syndrome.

Cerebellar ataxia and congenital disorder of glycosylation Ia (CDG-Ia) with normal routine CDG screening

Cerebellar ataxia can have many genetic causes among which are the congenital disorders of glycosylation type I (CDG-I). In this group of disorders, a multisystem phenotype is generally observed including the involvement of many organs, the endocrine, hematologic and central nervous systems. A few cases of CDG-Ia have been reported with a milder presentation, namely cerebellar hypoplasia as an isolated abnormality. To identify patients with a glycosylation disorder, isofocusing of plasma transferrin is routinely performed. Here, we describe two CDG-Ia patients,who presented with mainly ataxia and cerebellar hypoplasia and with a normal or only slightly abnormal transferrin isofocusing result. Surprisingly, the activity of the corresponding enzyme phosphomannomutase was clearly deficient in both leucocytes and fibroblasts. Therefore, in patients presenting with apparently recessive inherited ataxia caused by cerebellar hypoplasia and an unknown genetic aetiology after proper diagnostic work-up, we recommend the measurement of phosphomannomutase activity when transferrin isofocusing is normal or inconclusive.

Analytical evaluation of a new capillary electrophoresis method for carbohydrate-deficient transferrin measurement

Background Carbohydrate-deficient transferrin (CDT), the sum of a- and disialotransferrin, is considered the most efficient routine biological marker of alcohol abuse. In recent years, methods based on capillary zone electrophoresis (CZE) have been developed using specialized monocapillary systems. These are characterized by a high analytical detection level, counterbalanced by a poor productivity. We evaluated a new CZE method for CDT measurement on the Sebia Capillarys®, an eight-capillary system developed for routine serum capillary electrophoresis. Methods Precision and possible biases due to abnormal (low or high) transferrin levels or lipemic samples were assessed. Exactitude and precision were tested by comparison with a HPLC procedure acknowledged to be the most reliable to date. The validity of the manufacturer's cut-off was checked by measuring CDT in a population comprising abstaining patients, moderate alcohol consumers and alcohol abusers. Lastly, the method was compared to the routine %CDT TIA and N Latex CDT methods. Results The imprecision was 18.5% at the minimum detection level and decreased to 6.1% for high CDT values. No significant shift in the CDT results was observed in relation to abnormally low or high serum transferrin, or in lipemic samples. A high level of concordance was observed with the HPLC method used as reference. The results were strongly correlated with both other routine methods ( r > 0.90). The diagnostic values were comparable to the literature data, even if differences in the studied populations make difficult a direct comparison of the results. Our data suggested that the cut-off could be raised from 1.3% to 1.4% to reduce the number of false positive values without loss of diagnostic efficiency. Conclusions This Capillarys® method from Sebia showed good precision as compared to those published using other CZE methods. Capillarys® method correlated well with HPLC and two routine methods. However, we noticed significant bias at low CDT concentrations. Therefore, with the advantage of high throughput and full automation, these results indicate that the new method is a consistent alternative to the other methods proposed for routine CDT measurement.

Diagnosis of congenital disorders of glycosylation type‐I using protein chip technology

A method for the diagnosis of the congenital disorders of glycosylation type I (CDG-I) by SELDI-TOF-MS of serum transferrin immunocaptured on protein chip arrays is described. The underglycosylation of glycoproteins in CDG-I produces glycoforms of transferrin with masses lower than that of the normal fully glycosylated transferrin. Immobilisation of antitransferrin antibodies on reactive-surface protein chip arrays (RS100) selectively enriched transferrin by at least 100-fold and allowed the detection of patterns of transferrin glycoforms by SELDI-TOF-MS using approximately 0.3 microL of serum/plasma. Abnormal patterns of immunocaptured transferrin were detected in patients with known defects in glycosylation (CDG-Ia, CDG-Ib, CDG-Ic, CDG-If and CDG-Ih) and in patients in whom the basic defect has not yet been identified (CDG-Ix). The correction of the N-glycosylation defect in a patient with CDG-Ib after mannose therapy was readily detected. A patient who had an abnormal transferrin profile by IEF but a normal profile by SELDI-TOF-MS analysis was shown to have an amino acid polymorphism by sequencing transferrin by quadrupole-TOF MS. Complete agreement was obtained between analysis of immunocaptured transferrin by SELDI-TOF-MS and the IEF profile of transferrin, the clinical severity of the disease and the levels of aspartylglucosaminidase activity (a surrogate marker for the diagnosis of CDG-I). SELDI-TOF-MS of transferrin immunocaptured on protein chip arrays is a highly sensitive diagnostic method for CDG-I, which could be fully automated using microtitre plates and robotics.

Cryptogenic Liver Disease in Four Children: A Novel Congenital Disorder of Glycosylation

We investigated the metabolic defect(s) of four children who presented with isolated cryptogenic chronic liver disease, coagulopathy, and abnormalities of several unrelated serum glycoproteins. Analysis of the patients' serum glycoproteins and fibroblasts suggest they have a novel congenital disorder of glycosylation (CDG). All had abnormal transferrin (Tf) isoelectric focusing (IEF) profiles. More detailed analysis of Tf by electrospray ionization mass spectrometry (ESI-MS) showed a plethora of abnormal glycosylations that included loss of 1-2 sialic acids and 1-2 galactose units, typical of Group II defects. Tf from two patients also lacked 1-2 entire oligosaccharide chains, typical of Group One disorders. Total serum N-glycans were analyzed by HPLC and matrix-assisted laser desorption/ionization mass spectrometry and also showed increased proportion of neutral glycan chains lacking sialic acids and galactose units. Analysis of patient fibroblasts eliminated CDG-Ia, through CDG-Ih, -IL and CDG-IId. Our results suggest that a subset of children with clinically asymptomatic, cryptogenic hypertransaminasemia and/or liver steato-fibrosis may represent a novel type of CDG-X with an unknown defect(s). Clinicians are encouraged to test such patients for abnormal Tf glycosylation by ESI-MS.

Defective protein glycosylation in patients with cutis laxa syndrome

Congenital cutis laxa is a genetically heterogeneous condition presenting with loose and redundant skin folds, decreased elasticity of the skin, connective tissue involvement and a highly variable spectrum of associated features. The most common forms are inherited in an autosomal recessive or dominant fashion. Fibulin 5 and elastin mutations were detected in a limited number of patients, but in most cases the etiology is not known. Based on a previous observation of an abnormal transferrin isoelectric focusing pattern in a patient with cutis laxa indicating an N-glycosylation defect, we performed a screening for disorders of protein glycosylation in unrelated children with cutis laxa syndrome, including a recently developed test for defective O-glycosylation. Here, we describe five patients from consanguineous marriages with a cutis laxa syndrome with skeletal and joint involvement, developmental delay and neurological findings. Three of these five children have an inborn error of glycan biosynthesis affecting the synthesis of both N- and O-linked glycans. Two patients had normal glycosylation patterns. All known causes of secondary glycosylation disorders were excluded in the children. No mutations were found in the FBLN5 gene. In conclusion, we have identified a new combined glycosylation defect with a distinct clinical phenotype. Our results suggest that a combined defect of glycosylation might be a causative factor in congenital cutis laxa. This is the first report where abnormal N- and O-linked glycosylation is implicated in the etiology of cutis laxa syndrome.

Hemolytic Uremic Syndrome Attributable to Streptococcus pneumoniae Infection: A Novel Cause for Secondary Protein N-Glycan Abnormalities

Hypoglycosylation of glycoproteins is characteristic for congenital disorders of glycosylation (CDG) and may consist of partial or completely missing glycans (1). The major first test for CDG is isoelectric focusing (IEF) of plasma transferrin. The IEF pattern shows a cathodal shift because of the hypoglycosylation of the protein (2). Primary defects in the N-glycan biosynthetic pathway are known for nine CDG subtypes: CDG Ia–f and CDG IIa–c (3)(4)(5)(6)(7)(8). Transferrin hypoglycosylation can also be secondary to chronic alcohol abuse (9)(10), galactosemia (11), hereditary fructose intolerance (12), and severe liver pathology (9). In this report we describe the association of a transient abnormal transferrin N-glycosylation pattern in plasma and the clinical forms of hemolytic uremic syndrome (HUS) (13)(14)(15) associated with a Streptococcus pneumoniae infection (16). Five patients with HUS associated with a S. pneumoniae infection (age range, 9 months to 2 years) were studied. They fulfilled the criteria for HUS [hemolytic anemia with microangiopathic changes on peripheral blood smear (Burr cells), acute renal failure, and thrombocytopenia] and presented with pneumonia or meningitis. S. pneumoniae was isolated from body fluids of the five patients. We also studied three patients with HUS attributable to verocytotoxin-producing Escherichia coli (VTEC) infection and one case of familial HUS of unknown etiology. von Willebrand factor cleaving protease deficiency and a defect in factor H were excluded in this patient. The sialotransferrin fractions for the five S. pneumoniae -associated HUS cases and healthy controls are shown in Table 1⇓ and Fig. 1⇓ . In healthy individuals (Fig. 1A⇓ , lane 1), the major transferrin form is the tetrasialo form. In all HUS cases associated with S. pneumoniae , the tetrasialotransferrin fraction was markedly decreased and the a-, mono-, and …