CDG-IL: an infant with a novel mutation in the ALG9 gene and additional phenotypic features

Heterozygosity of ALG9 in Association with Autosomal Dominant Polycystic Liver Disease

α-1,2-mannosyltransferase (ALG9) germline variants are linked to autosomal dominant polycystic kidney disease (ADPKD). Many individuals affected with ADPKD possess polycystic livers as a common extrarenal manifestation. We performed whole exome sequencing in a female with autosomal dominant polycystic liver disease (ADPLD) without kidney cysts and established the presence of a heterozygous missense variant (c.677G>C p.(Gly226Ala)) in ALG9. In silico pathogenicity prediction and 3D protein modeling determined this variant as pathogenic. Loss of heterozygosity is regularly seen in liver cyst walls. Immunohistochemistry indicated the absence of ALG9 in liver tissue from this patient. ALG9 expression was absent in cyst wall lining from ALG9- and PRKCSH-caused ADPLD patients but present in the liver cyst lining derived from an ADPKD patient with a PKD2 variant. Thus, heterozygous pathogenic variants in ALG9 are also associated with ADPLD. Somatic loss of heterozygosity of the ALG9 enzyme was seen in the ALG9 patient but also in ADPLD patients with a different genetic background. This expanded the phenotypic spectrum of ADPLD to ALG9.

Metabolic Cardiomyopathies and Cardiac Defects in Inherited Disorders of Carbohydrate Metabolism: A Systematic Review

Heart failure (HF) is a progressive chronic disease that remains a primary cause of death worldwide, affecting over 64 million patients. HF can be caused by cardiomyopathies and congenital cardiac defects with monogenic etiology. The number of genes and monogenic disorders linked to development of cardiac defects is constantly growing and includes inherited metabolic disorders (IMDs). Several IMDs affecting various metabolic pathways have been reported presenting cardiomyopathies and cardiac defects. Considering the pivotal role of sugar metabolism in cardiac tissue, including energy production, nucleic acid synthesis and glycosylation, it is not surprising that an increasing number of IMDs linked to carbohydrate metabolism are described with cardiac manifestations. In this systematic review, we offer a comprehensive overview of IMDs linked to carbohydrate metabolism presenting that present with cardiomyopathies, arrhythmogenic disorders and/or structural cardiac defects. We identified 58 IMDs presenting with cardiac complications: 3 defects of sugar/sugar-linked transporters (GLUT3, GLUT10, THTR1); 2 disorders of the pentose phosphate pathway (G6PDH, TALDO); 9 diseases of glycogen metabolism (GAA, GBE1, GDE, GYG1, GYS1, LAMP2, RBCK1, PRKAG2, G6PT1); 29 congenital disorders of glycosylation (ALG3, ALG6, ALG9, ALG12, ATP6V1A, ATP6V1E1, B3GALTL, B3GAT3, COG1, COG7, DOLK, DPM3, FKRP, FKTN, GMPPB, MPDU1, NPL, PGM1, PIGA, PIGL, PIGN, PIGO, PIGT, PIGV, PMM2, POMT1, POMT2, SRD5A3, XYLT2); 15 carbohydrate-linked lysosomal storage diseases (CTSA, GBA1, GLA, GLB1, HEXB, IDUA, IDS, SGSH, NAGLU, HGSNAT, GNS, GALNS, ARSB, GUSB, ARSK). With this systematic review we aim to raise awareness about the cardiac presentations in carbohydrate-linked IMDs and draw attention to carbohydrate-linked pathogenic mechanisms that may underlie cardiac complications.

Gillessen-Kaesbach-Nishimura syndrome in two fetuses from Turkey

Gillessen-Kaesbach-Nishimura syndrome (GIKANIS) is a congenital disease of glycosylation (CDG) linked to the ALG9 gene. GIKANIS is a lethal disorder characterized by atypical facial features, generalized skeletal changes with shortening of the long bones with broad, round metaphyses, round ilia, and deficient ossification of the skull, cervical spine and pubic bones, and visceral abnormalities including polycystic kidneys and congenital cardiac defects. GIKANIS is caused by a homozygous splicing variant (c.1173 + 2 T > A) leading to skipping of exon 10, frameshift, and premature termination codon of the ALG9 gene. To our best knowledge, only two affected families with confirmed molecular analyses have been reported. We present an additional report on two siblings with the same mutation, emphasizing the prenatal ultrasonographic features. Their facial and skeletal manifestations recapitulated those previously reported. Ultrasonography revealed polycystic kidneys and unbalanced atrioventricular septal defect (AVSD) with transposition of the great arteries.

Missense variant c.1460 T > C (p.L487P) enhances protein degradation of ER mannosyltransferase ALG9 in two new ALG9-CDG patients presenting with West syndrome and review of the literature

ALG9-CDG is a CDG-I defect within the group of Congenital Disorders of Glycosylation (CDG). We here describe the clinical symptoms of two new and unrelated ALG9-CDG patients, both carrying the novel homozygous missense variant c.1460 T > C (p.L487P) in the ALG9 gene which led to global developmental delay, psychomotor disability, facial dysmorphisms, brain and heart defects, hearing loss, hypotonia, as well as feeding problems. New clinical symptoms comprised West syndrome with hypsarrhythmia. Quantitative RT-PCR analysis revealed a significantly enhanced ALG9 mRNA transcript level, whereas the protein amount in fibroblasts was significantly reduced. This could be ascribed to a stronger degradation of the mutated ALG9 protein in patient fibroblasts. Lipid-linked oligosaccharide analysis showed an ALG9-CDG characteristic accumulation of Man₆GlcNAc₂-PP-dolichol and Man₈GlcNAc₂-PP-dolichol in patient cells. The clinical findings of our patients and of all previously published ALG9-CDG patients are brought together to further expand the knowledge about this rare N-glycosylation disorder. SYNOPSIS: Homozygosity for p.L487P in ALG9 causes protein degradation and leads to West syndrome.

Pansomatostatin Agonist Pasireotide Long-Acting Release for Patients with Autosomal Dominant Polycystic Kidney or Liver Disease with Severe Liver Involvement: A Randomized Clinical Trial

BACKGROUND AND OBJECTIVES

We assessed safety and efficacy of another somatostatin receptor analog, pasireotide long-acting release, in severe polycystic liver disease and autosomal dominant polycystic kidney disease. Pasireotide long-acting release, with its broader binding profile and higher affinity to known somatostatin receptors, has potential for greater efficacy.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Individuals with severe polycystic liver disease were assigned in a 2:1 ratio in a 1-year, double-blind, randomized trial to receive pasireotide long-acting release or placebo. Primary outcome was change in total liver volume; secondary outcomes were change in total kidney volume, eGFR, and quality of life.

RESULTS

Of 48 subjects randomized, 41 completed total liver volume measurements (n=29 pasireotide long-acting release and n=12 placebo). From baseline, there were -99±189 ml/m absolute and -3%±7% change in annualized change in height-adjusted total liver volume (from 2582±1381 to 2479±1317 ml/m) in the pasireotide long-acting release group compared with 136±117 ml/m absolute and 6%±7% increase (from 2387±759 to 2533±770 ml/m) in placebo (P<0.001 for both). Total kidney volumes decreased by -12±34 ml/m and -1%±4% in pasireotide long-acting release compared with 21±21 ml/m and 4%±5% increase in the placebo group (P=0.05 for both). Changes in eGFR were similar between groups. Among the n=48 randomized, adverse events included hyperglycemia (26 of 33 [79%] in pasireotide long-acting release versus four of 15 [27%] in the placebo group; P<0.001), and among the 47 without diabetes at baseline, 19 of 32 (59%) in the pasireotide long-acting release group versus one of 15 (7%) in the placebo group developed diabetes (P=0.001).

CONCLUSIONS

Another somatostatin analog, pasireotide long-acting release, slowed progressive increase in both total liver volume/total kidney volume growth rates without affecting GFR decline. Participants experienced higher frequency of adverse events (hyperglycemia and diabetes).

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

Pasireotide LAR in Severe Polycystic Liver Disease, NCT01670110 PODCAST: This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2020_08_28_CJN13661119.mp3.

ALG9-CDG: New clinical case and review of the literature

Congenital disorders of glycosylation (CDG) are a group of metabolic diseases resulting from defects in glycan synthesis or processing. The number of subgroups and their phenotypic spectrums continue to expand with most related to deficiencies of N-glycosylation. ALG9-CDG (previously CDG-IL) is the result of a mutation in ALG9. This gene encodes the enzyme alpha-1,2-mannosyltransferase. To date, a total of 10 patients from 6 different families have been reported with one of four ALG9 mutations. Seven of these patients had a similar phenotype with failure to thrive, dysmorphic features, seizures, hepatic and/or renal cysts; the other three patients died in utero from a lethal skeletal dysplasia. This report describes an additional patient with ALG9-CDG who has a milder phenotype. This patient is a term female born to Caucasian, Canadian, non-consanguineous parents of Scottish decent. Prenatally, dysmorphic features, numerous renal cysts and minor cardiac malformations were detected. Post-natally, dysmorphic features included shallow orbits, micrognathia, hypoplastic nipples, talipes equinovarus, lipodystrophy and cutis marmorata. She developed failure to thrive and seizures. The metabolic work-up included analysis of a transferrin isoelectric focusing, which showed a type 1 pattern. This was confirmed by glycan profiling, which identified ahomozygous mutation in ALG9, c.860A > G (p.Tyr287Cys) (NM_1234567890). This had been previously published as a pathogenic mutation in two Canadian patients. Our goal is to contribute to the growing body of knowledge for this disorder by describing the phenotypic spectrum and providing further insight on prognosis.

Cardiac complications of congenital disorders of glycosylation (CDG): a systematic review of the literature

Congenital disorders of glycosylation (CDG) are inborn errors of metabolism due to protein and lipid hypoglycosylation. This rapidly growing family of genetic diseases comprises 103 CDG types, with a broad phenotypic diversity ranging from mild to severe poly-organ -system dysfunction. This literature review summarizes cardiac involvement, reported in 20% of CDG. CDG with cardiac involvement were divided according to the associated type of glycosylation: N-glycosylation, O-glycosylation, dolichol synthesis, glycosylphosphatidylinositol (GPI)-anchor biosynthesis, COG complex, V-ATPase complex, and other glycosylation pathways. The aim of this review was to document and interpret the incidence of heart disease in CDG patients. Heart disorders were grouped into cardiomyopathies, structural defects, and arrhythmogenic disorders. This work may contribute to improved early management of cardiac complications in CDG.

Isolated polycystic liver disease genes define effectors of polycystin-1 function

Dominantly inherited isolated polycystic liver disease (PCLD) consists of liver cysts that are radiologically and pathologically identical to those seen in autosomal dominant polycystic kidney disease, but without clinically relevant kidney cysts. The causative genes are known for fewer than 40% of PCLD index cases. Here, we have used whole exome sequencing in a discovery cohort of 102 unrelated patients who were excluded for mutations in the 2 most common PCLD genes, PRKCSH and SEC63, to identify heterozygous loss-of-function mutations in 3 additional genes, ALG8, GANAB, and SEC61B. Similarly to PRKCSH and SEC63, these genes encode proteins that are integral to the protein biogenesis pathway in the endoplasmic reticulum. We inactivated these candidate genes in cell line models to show that loss of function of each results in defective maturation and trafficking of polycystin-1, the central determinant of cyst pathogenesis. Despite acting in a common pathway, each PCLD gene product demonstrated distinct effects on polycystin-1 biogenesis. We also found enrichment on a genome-wide basis of heterozygous mutations in the autosomal recessive polycystic kidney disease gene PKHD1, indicating that adult PKHD1 carriers can present with clinical PCLD. These findings define genetic and biochemical modulators of polycystin-1 function and provide a more complete definition of the spectrum of dominant human polycystic diseases.

Liver involvement in congenital disorders of glycosylation (CDG). A systematic review of the literature

Congenital disorders of glycosylation (CDG) are a rapidly growing family of genetic diseases caused by defects in glycosylation. Nearly 100 CDG types are known so far. Patients present a great phenotypic diversity ranging from poly- to mono-organ/system involvement and from very mild to extremely severe presentation. In this literature review, we summarize the liver involvement reported in CDG patients. Although liver involvement is present in only a minority of the reported CDG types (22 %), it can be debilitating or even life-threatening. Sixteen of the patients we collated here developed cirrhosis, 10 had liver failure. We distinguish two main groups: on the one hand, the CDG types with predominant or isolated liver involvement including MPI-CDG, TMEM199-CDG, CCDC115-CDG, and ATP6AP1-CDG, and on the other hand, the CDG types associated with liver disease but not as a striking, unique or predominant feature, including PMM2-CDG, ALG1-CDG, ALG3-CDG, ALG6-CDG, ALG8-CDG, ALG9-CDG, PGM1-CDG, and COG-CDG. This review aims to facilitate CDG patient identification and to understand CDG liver involvement, hopefully leading to earlier diagnosis, and better management and treatment.

Classical Galactosaemia and CDG, the N-Glycosylation Interface. A Review

Classical galactosaemia is a rare disorder of carbohydrate metabolism caused by galactose-1-phosphate uridyltransferase (GALT) deficiency (EC 2.7.7.12). The disease is life threatening if left untreated in neonates and the only available treatment option is a long-term galactose restricted diet. While this is lifesaving in the neonate, complications persist in treated individuals, and the cause of these, despite early initiation of treatment, and shared GALT genotypes remain poorly understood. Systemic abnormal glycosylation has been proposed to contribute substantially to the ongoing pathophysiology. The gross N-glycosylation assembly defects observed in the untreated neonate correct over time with treatment. However, N-glycosylation processing defects persist in treated children and adults.Congenital disorders of glycosylation (CDG) are a large group of over 100 inherited disorders affecting largely N- and O-glycosylation.In this review, we compare the clinical features observed in galactosaemia with a number of predominant CDG conditions.We also summarize the N-glycosylation abnormalities, which we have described in galactosaemia adult and paediatric patients, using an automated high-throughput HILIC-UPLC analysis of galactose incorporation into serum IgG with analysis of the corresponding N-glycan gene expression patterns and the affected pathways.

Further Delineation of the ALG9-CDG Phenotype

ALG9-CDG is one of the less frequently reported types of CDG. Here, we summarize the features of six patients with ALG9-CDG reported in the literature and report the features of four additional patients. The patients presented with drug-resistant infantile epilepsy, hypotonia, dysmorphic features, failure to thrive, global developmental disability, and skeletal dysplasia. One patient presented with nonimmune hydrops fetalis. A brain MRI revealed global atrophy with delayed myelination. Exome sequencing identified a novel homozygous mutation c.1075G>A, p.E359K of the ALG9 gene. The results of our analysis of these patients expand the knowledge of ALG9-CDG phenotype.

A novel phenotype in N-glycosylation disorders: Gillessen-Kaesbach-Nishimura skeletal dysplasia due to pathogenic variants in ALG9

A rare lethal autosomal recessive syndrome with skeletal dysplasia, polycystic kidneys and multiple malformations was first described by Gillessen-Kaesbach et al and subsequently by Nishimura et al. The skeletal features uniformly comprise a round pelvis, mesomelic shortening of the upper limbs and defective ossification of the cervical spine. We studied two unrelated families including three affected fetuses with Gillessen-Kaesbach-Nishimura syndrome using whole-exome and Sanger sequencing, comparative genome hybridization and homozygosity mapping. All affected patients were shown to have a novel homozygous splice variant NM_024740.2: c.1173+2T>A in the ALG9 gene, encoding alpha-1,2-mannosyltransferase, involved in the formation of the lipid-linked oligosaccharide precursor of N-glycosylation. RNA analysis demonstrated skipping of exon 10, leading to shorter RNA. Mass spectrometric analysis showed an increase in monoglycosylated transferrin as compared with control tissues, confirming that this is a congenital disorder of glycosylation (CDG). Only three liveborn children with ALG9-CDG have been previously reported, all with missense variants. All three suffered from intellectual disability, muscular hypotonia, microcephaly and renal cysts, but none had skeletal dysplasia. Our study shows that some pathogenic variants in ALG9 can present as a lethal skeletal dysplasia with visceral malformations as the most severe phenotype. The skeletal features overlap with that previously reported for ALG3- and ALG12-CDG, suggesting that this subset of glycosylation disorders constitutes a new diagnostic group of skeletal dysplasias.

Mass spectrometric analysis of neutral and anionic N-glycans from a Dictyostelium discoideum model for human congenital disorder of glycosylation CDG IL

The HL241 mutant strain of the cellular slime mold Dictyostelium discoideum is a potential model for human congenital disorder of glycosylation type IL (ALG9-CDG) and has been previously predicted to possess a lower degree of modification of its N-glycans with anionic moieties than the parental wild-type. In this study, we first showed that this strain has a premature stop codon in its alg9 mannosyltransferase gene compatible with the occurrence of truncated N-glycans. These were subject to an optimized analytical workflow, considering that the mass spectrometry of acidic glycans often presents challenges due to neutral loss and suppression effects. Therefore, the protein-bound N-glycans were first fractionated, after serial enzymatic release, by solid phase extraction. Then primarily single glycan species were isolated by mixed hydrophilic-interaction/anion-exchange or reversed-phase HPLC and analyzed using chemical and enzymatic treatments and MS/MS. We show that protein-linked N-glycans of the mutant are of reduced size as compared to those of wild-type AX3, but still contain core α1,3-fucose, intersecting N-acetylglucosamine, bisecting N-acetylglucosamine, methylphosphate, phosphate, and sulfate residues. We observe that a single N-glycan can carry up to four of these six possible modifications. Due to the improved analytical procedures, we reveal fuller details regarding the N-glycomic potential of this fascinating model organism.

Evolutionarily conserved glycan signal to degrade aberrant brassinosteroid receptors in Arabidopsis

Asparagine-linked glycans (N-glycans) are crucial signals for protein folding, quality control, and endoplasmic reticulum (ER)-associated degradation (ERAD) in yeast and mammals. Although similar ERAD processes were reported in plants, little is known about their biochemical mechanisms, especially their relationships with N-glycans. Here, we show that a missense mutation in the Arabidopsis EMS-mutagenized bri1 suppressor 3 (EBS3) gene suppresses a dwarf mutant, bri1-9, the phenotypes of which are caused by ER retention and ERAD of a brassinosteroid receptor, BRASSINOSTEROID-INSENSITIVE 1 (BR1). EBS3 encodes the Arabidopsis ortholog of the yeast asparagine-linked glycosylation 9 (ALG9), which catalyzes the ER luminal addition of two terminal α1,2 mannose (Man) residues in assembling the three-branched N-glycan precursor [glucose(Glc)](3)(Man)(9)[N-acetylglucosamine(GlcNAc)](2). Consistent with recent discoveries revealing the importance of the Glc(3)Man(9)GlcNAc(2) C-branch in generating an ERAD signal, the ebs3-1 mutation prevents the Glc(3)Man(9)GlcNAc(2) assembly and inhibits the ERAD of bri1-9. By contrast, overexpression of EBS4 in ebs3-1 bri1-9, which encodes the Arabidopsis ortholog of the yeast ALG12 catalyzing the ER luminal α1,6 Man addition, adds an α1,6 Man to the truncated N-glycan precursor accumulated in ebs3-1 bri1-9, promotes the bri1-9 ERAD, and neutralizes the ebs3-1 suppressor phenotype. Furthermore, a transfer (T)-DNA insertional alg3-T2 mutation, which causes accumulation of an even smaller N-glycan precursor carrying a different exposed α1,6 Man, promotes the ERAD of bri1-9 and enhances its dwarfism. Taken together, our results strongly suggest that the glycan signal to mark an ERAD client in Arabidopsis is likely conserved to be an α1,6 Man-exposed N-glycan.

Congenital protein hypoglycosylation diseases

Glycosylation is an essential process by which sugars are attached to proteins and lipids. Complete lack of glycosylation is not compatible with life. Because of the widespread function of glycosylation, inherited disorders of glycosylation are multisystemic. Since the identification of the first defect on N-linked glycosylation in the 1980s, there are over 40 different congenital protein hypoglycosylation diseases. This review will include defects of N-linked glycosylation, O-linked glycosylation and disorders of combined N- and O-linked glycosylation.

Metabolic and monogenic causes of seizures in neonates and young infants

Seizures in neonates or young infants present a frequent diagnostic challenge. After exclusion of acquired causes, disturbances of the internal homeostasis and brain malformations, the physician must evaluate for inborn errors of metabolism and for other non-malformative genetic disorders as the cause of seizures. The metabolic causes can be categorized into disorders of neurotransmitter metabolism, disorders of energy production, and synthetic or catabolic disorders associated with brain malformation, dysfunction and degeneration. Other genetic conditions involve channelopathies, and disorders resulting in abnormal growth, differentiation and formation of neuronal populations. These conditions are important given their potential for treatment and the risk for recurrence in the family. In this paper, we will succinctly review the metabolic and genetic non-malformative causes of seizures in neonates and infants less than 6 months of age. We will then provide differential diagnostic clues and a practical paradigm for their evaluation.

Congenital disorders of glycosylation in hepatology: the example of polycystic liver disease

Autosomal dominant polycystic liver disease (PCLD) is a rare progressive disorder characterized by an increased liver volume due to many (>20) fluid-filled cysts of biliary origin. Disease causing mutations in PRKCSH or SEC63 are found in approximately 25% of the PCLD patients. Both gene products function in the endoplasmic reticulum, however, the molecular mechanism behind cyst formation remains to be elucidated. As part of the translocon complex, SEC63 plays a role in protein import into the ER and is implicated in the export of unfolded proteins to the cytoplasm during ER-associated degradation (ERAD). PRKCSH codes for the beta-subunit of glucosidase II (hepatocystin), which cleaves two glucose residues of Glc(3)Man(9)GlcNAc(2) N-glycans on proteins. Hepatocystin is thereby directly involved in the protein folding process by regulating protein binding to calnexin/calreticulin in the ER. A separate group of genetic diseases affecting protein N-glycosylation in the ER is formed by the congenital disorders of glycosylation (CDG). In distinct subtypes of this autosomal recessive multisystem disease specific liver symptoms have been reported that overlap with PCLD. Recent research revealed novel insights in PCLD disease pathology such as the absence of hepatocystin from cyst epithelia indicating a two-hit model for PCLD cystogenesis. This opens the way to speculate about a recessive mechanism for PCLD pathophysiology and shared molecular pathways between CDG and PCLD. In this review we will discuss the clinical-genetic features of PCLD and CDG as well as their biochemical pathways with the aim to identify novel directions of research into cystogenesis.

Congenital disorders of glycosylation: an update on defects affecting the biosynthesis of dolichol-linked oligosaccharides

Defects in the biosynthesis of the oligosaccharide precursor for N-glycosylation lead to decreased occupancy of glycosylation sites and thereby to diseases known as congenital disorders of glycosylation (CDG). In the last 20 years, approximately 1,000 CDG patients have been identified presenting with multiple organ dysfunctions. This review sets the state of the art by listing all mutations identified in the 15 genes (PMM2, MPI, DPAGT1, ALG1, ALG2, ALG3, ALG9, ALG12, ALG6, ALG8, DOLK, DPM1, DPM3, MPDU1, and RFT1) that yield a deficiency of dolichol-linked oligosaccharide biosynthesis. The present analysis shows that most mutations lead to substitutions of strongly conserved amino acid residues across eukaryotes. Furthermore, the comparison between the different forms of CDG affecting dolichol-linked oligosaccharide biosynthesis shows that the severity of the disease does not relate to the position of the mutated gene along this biosynthetic pathway.

Cardiomyopathy in the congenital disorders of glycosylation (CDG): a case of late presentation and literature review

The congenital disorders of glycosylation (CDG) are a recently described group of inherited multisystem disorders characterized by defects predominantly of N- and O-glycosylation of proteins. Cardiomyopathy in CDG has previously been described in several subtypes; it is usually associated with high morbidity and mortality and the majority of cases present in the first 2 years of life. This is the first case with presentation in late childhood and the article reviews current literature. An 11-year-old female with a background of learning difficulties presented in cardiac failure secondary to severe dilated cardiomyopathy. Prior to the diagnosis of CDG, her condition deteriorated; she required mechanical support (Excor Berlin Heart) and was listed for cardiac transplant. Investigations included screening for glycosylation disorders, and isoelectric focusing of transferrin revealed an abnormal type 1 pattern. Analysis of phosphomannomutase and phosphomannose isomerase showed normal enzyme activity, excluding PMM2 (CDG Ia) and MPI (CDG Ib). Lipid-linked oligosaccharide and mutational studies have not yet defined the defect. Despite aggressive therapy there were persistent difficulties achieving adequate anticoagulation and she developed multiple life-threatening thrombotic complications. She was removed from the transplant list and died from overwhelming sepsis 5 weeks following admission. This case emphasizes the need to screen all children with an undiagnosed cardiomyopathy for CDG, regardless of age, and where possible to exclude CDG before the use of cardiac bridging devices. It highlights the many practical and ethical challenges that may be encountered where clinical knowledge and experience are still evolving.

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.

Congenital Disorders of Glycosylation: A Rapidly Expanding Disease Family

Congenital disorders of glycosylation (CDG) are a large family of genetic diseases resulting from defects in the synthesis of glycans and in the attachment of glycans to other compounds. These disorders cause a wide range of human diseases, with examples emanating from all medical subspecialties. Since our 2001 review on CDG ( 36 ), this field has seen substantial growth: The number of N-glycosylation defects has doubled (from 6 to 12), five new O-glycosylation defects have been added to the two previously known ones, three combined N- and O-glycosylation defects have been identified, the first lipid glycosylation defects have been discovered, and a new domain, that of the hyperglycosylation defects, has been introduced. A number of CDG are due to defects in enzymes with a putative glycosyltransferase function. There is also a growing group of patients with unidentified defects (CDG-x), some with typical clinical presentations and others with presentations not seen before in CDG. This review focuses on the clinical, biochemical, and genetic characteristics of CDG and on advances expected in their future study and clinical management.

Congenital disorders of N-glycosylation including diseases associated with O- as well as N-glycosylation defects

The congenital disorders of N-glycosylation (CDG), a steadily increasing group of multi-systemic disorders, have severe clinical implications in infancy and early childhood. The various inborn errors responsible adversely affect N-glycosylation of lysosomal proteins because of either failing assembly of lipid-linked (LL) oligosaccharides (OS) in the endoplasmic reticulum, CDG Type I, or faulty processing of the asparagines (N)-linked OS in the ER and in the Golgi, CDG Type II. The overlap of phenotypes precludes specific clinical delineation. Isoelectric focusing (IEF) of plasma transferrin remains a valuable, albeit imperfect, screening tool. IEF of plasma ApoC-III protein, introduced O-glycosylation defects that delineated some new CDGs due to mutations of both N- and O-glycosylation. Only CDG-Ib is amenable to treatment with free mannose supplementation. Hence, early specific diagnosis of any one entity is crucial for genetic counseling and elective preventive measures.

Common variations in ALG9 are not associated with bipolar I disorder: a family-based study

Background

A mannosyltransferase gene (ALG9, DIBD1) at chromosome band 11q23 was previously identified to be disrupted by a balanced chromosomal translocation t(9;11)(p24;q23) co-segregating with bipolar affective disorder in a small family. Inborn ALG9 deficiency (congenital disorders of glycosylation type IL) is associated with progressive microcephaly, seizures, developmental delay, and hepatomegaly. It is unknown whether common variations of ALG9 predispose to bipolar affective disorder.

Methods

We tested five polymorphic markers spanning ALG9 (three intragenic and one upstream microsatellite repeats and one common missense variation, V289I (rs10502151) for their association with bipolar I disorder in two pedigree series. The NIMH (National Institute of Mental Health) pedigrees had a total of 166 families showing transmissions to 250 affected offspring, whereas The PITT (The University of Pittsburgh) pedigrees had a total of 129 families showing transmissions to 135 cases. We used transmission disequilibrium test for the association analyses.

Results

We identified three common and distinct haplotypes spanning the ALG9 gene. We found no statistically-significant evidence of transmission disequilibrium of marker alleles or multi-marker haplotypes to the affected offspring with bipolar I disorder.

Conclusion

These results suggest that common variations in ALG9 do not play a major role in predisposition to bipolar affective disorder.

The congenital disorders of glycosylation: a multifaceted group of syndromes

The congenital disorders of glycosylation (CDG) are a rapidly expanding group of metabolic syndromes with a wide symptomatology and severity. They all stem from deficient N-glycosylation of proteins. To date the group contains 18 different subtypes: 12 of Type I (disrupted synthesis of the lipid-linked oligosaccharide precursor) and 6 of Type II (malfunctioning trimming/processing of the protein-bound oligosaccharide). Main features of CDG involve psychomotor retardation; ataxia; seizures; retinopathy; liver fibrosis; coagulopathies; failure to thrive; dysmorphic features, including inverted nipples and subcutaneous fat pads; and strabismus. No treatment currently is available for the vast majority of these syndromes (CDG-Ib and CDG-IIc are exceptions), even though attempts to synthesize drugs for the most common subtype, CDG-Ia, have been made. In this review we will discuss the individual syndromes, with focus on their neuronal involvement, available and possible treatments, and future directions.

Metabolic mimics: the disorders of N-linked glycosylation

N-linked glycosylation is essential for normal cellular function. Defects have now been described in eighteen genes that participate in the process. All give rise to complex multisystem diseases which, with a few exceptions, primarily involve the nervous system. Frequent features of these disorders include developmental delay, ataxia, seizures, stroke-like episodes, recurrent infections, coagulopathy and dysmorphism. Most cases can be detected by screening carbohydrate-deficient transferrin, but definitive diagnosis requires enzymatic and molecular confirmation, frequently in collaboration with a research glycobiologist.