Skin manifestations in CDG

Missense variant in PIGM associated with severe cystic encephalomalacia and portal vein thrombosis: Phenotypic and genotypic expansion of the glycosylphosphatidylinositol biosynthesis defect-1 (GPIBD1)

Glycosylphosphatidylinositols (GPIs) are a type of glycolipid responsible for anchoring many important proteins to the cell membrane surface. Defects in the synthesis of GPIs can lead to a group of multisystem disorders known as the inherited GPI deficiencies (IGDs). Homozygosity for the c.-270C > G variant in the promoter of PIGM has been associated with a IGD subtype known as glycosylphosphatidylinositol biosynthesis defect-1 (GPIBD1). The several cases reported in the literature have been described to have a milder neurologic phenotype in comparison to the other IGDs and have been treated with sodium phenylbutyrate with some degree of success. These patients typically present with portal and hepatic vein thrombosis and mostly develop absence seizures. Here we describe a patient homozygous for a nonsynonymous variant in PIGM who deceased at 9 weeks of life and had multiple physical dysmorphisms (rocker bottom feet, midline cleft palate, thickened and lichenified skin), portal vein thrombosis, CNS structural anomalies (progressive multicystic encephalomalacia and ventriculomegaly), and a neurological phenotype of a diffuse encephalopathy. This is the first known case report of a PIGM-related IGD/CDG due to a coding variant.

Transcriptomic analysis identifies dysregulated pathways and therapeutic targets in PMM2-CDG

PMM2-CDG (MIM # 212065), the most common congenital disorder of glycosylation, is caused by the deficiency of phosphomannomutase 2 (PMM2). It is a multisystemic disease of variable severity that particularly affects the nervous system; however, its molecular pathophysiology remains poorly understood. Currently, there is no effective treatment. We performed an RNA-seq based transcriptomic study using patient-derived fibroblasts to gain insight into the mechanisms underlying the clinical symptomatology and to identify druggable targets. Systems biology methods were used to identify cellular pathways potentially affected by PMM2 deficiency, including Senescence, Bone regulation, Cell adhesion and Extracellular Matrix (ECM) and Response to cytokines. Functional validation assays using patients' fibroblasts revealed defects related to cell proliferation, cell cycle, the composition of the ECM and cell migration, and showed a potential role of the inflammatory response in the pathophysiology of the disease. Furthermore, treatment with a previously described pharmacological chaperone reverted the differential expression of some of the dysregulated genes. The results presented from transcriptomic data might serve as a platform for identifying therapeutic targets for PMM2-CDG, as well as for monitoring the effectiveness of therapeutic strategies, including pharmacological candidates and mannose-1-P, drug repurposing.

Syndromic ichthyoses

Inherited ichthyoses are classified as Mendelian disorders of cornification (MEDOC), which are further defined on the basis of clinical and genetic features and can be divided into non-syndromic and syndromic forms. To date, mutations in more than 30 genes are known to result in various types of syndromic ichthyoses, which, in addition to mostly generalised scaling and hyperkeratosis of the skin, also show additional organ involvement. The syndromic ichthyoses are generally very rare and are classified based on the mode of inheritance, and can be further subdivided according to the predominant symptoms. In our review we provide a concise overview of the most prevalent syndromic forms of ichthyosis within each subgroup. We emphasize the importance of the clinical assessment of complex syndromes even in the era of genetic testing as a first-tier diagnostic and specifically the need to actively assess potential organ involvement in patients with ichthyosis, thereby enabling efficient diagnostic and therapeutic approaches and timely access to specialized centers for rare disorders of cornifications. As part of the Freiburg Center for Rare Diseases a Center for Cornification Disorders was recently established with collaboration of the Institute of Human Genetics and the Department of Dermatology. An early diagnosis of syndromes will be of direct benefit to the patient regarding interventional and therapeutic measures e. g. in syndromes with cardiac or metabolic involvement and allows informed reproductive options and access to prenatal and preimplantation genetic diagnosis in the family.

Multitissue Integrative Analysis Identifies Susceptibility Genes for Atopic Dermatitis

Atopic dermatitis (AD) is a chronic relapsing inflammatory skin disease with multiple environmental and genetic factors involved in its etiology. Although lots of genetic loci associated with AD have been reported by GWASs, only a small part of phenotypic variations can be explained. To identify additional susceptibility genes on AD, we conducted a large-scale transcriptome-wide association study using a joint-tissue imputation approach in ∼840,000 European individuals combined with six precomputed gene expression weights of four AD-relevant tissues, including skin fibroblast, lymphocyte, and whole blood. The Mendelian randomization causal inference analysis was performed to estimate the causal effect of transcriptome-wide association study‒identified genes. We identified 51 genes significantly associated with AD after Bonferroni corrections, and 19 genes showed putatively causal associations such as an established gene FLG (P = 3.98 × 10^‒10) and seven genes that have not been implicated in previous transcriptome-wide association studies, such as AQP3 (P = 4.43 × 10^‒7) and PDCD1 (P = 7.66 × 10^‒7). Among them, four genes (AQP3, PDCD1, ADCY3, and DOLPP1) were further supported in differential expression analyses or the Mouse Genome Informatics database. Overall, our study identified susceptibility genes associated with AD, providing, to our knowledge, previously unreported clues in revealing the genetic mechanisms in AD.

DDOST-CDG: Clinical and molecular characterization of a third patient with a milder and a predominantly movement disorder phenotype

Congenital disorders of glycosylation (CDG) are a group of heterogeneous inherited metabolic disorders affecting posttranslational protein modification. DDOST-CDG, caused by biallelic pathogenic variants in DDOST which encodes dolichyl-diphospho-oligosaccharide-protein glycosyltransferase, a subunit of N-glycosylation oligosaccharyltransferase (OST) complex, is an ultra-rare condition that has been described in two patients only. The main clinical features in the two reported patients include profound developmental delay, failure to thrive, and hypotonia. In addition, both patients had abnormal transferrin glycosylation. Here, we report an 18-year-old male who presented with moderate developmental delay, progressive opsoclonus, myoclonus, ataxia, tremor, and dystonia. Biochemical studies by carbohydrate deficient transferrin analysis showed a type I CDG pattern. Exome sequencing identified compound heterozygous variants in DDOST: a maternally inherited variant, c.1142dupT (p.Leu381Phefs*11), and a paternally inherited variant, c.661 T > C (p.Ser221Pro). Plasma N-glycan profiling showed mildly increased small high mannose glycans including Man0-5 GlcNAc2, a pattern consistent with what was previously reported in DDOST-CDG or defects in other subunits of OST complex. Western blot analysis on patient's fibroblasts revealed decreased expression of DDOST and reduced intracellular N-glycosylation, as evident by the biomarkers ICAM-1 and LAMP2. Our study highlights the clinical variability, expands the clinical and biochemical phenotypes, and describes new genotype, which all are essential for diagnosing and managing patients with DDOST-CDG.

Identification and characterization of a new variation in DPM2 gene in two Chinese siblings with mild intellectual impairment

Introduction: Congenital disorders of glycosylation (CDGs) are a genetically heterogeneous group of metabolic disorders caused by abnormal protein or lpid glycosylation. DPM2 is one subunit of a heterotrimeric complex for dolichol-phosphatemannose synthase (DPMS), a key enzyme in glycosylation, and only four patients with DPM2-CDG have been reported. Methods: Whole-exome sequencing (WES) was performed in a Chinese family having two siblings with a mild form of DPM2-CDG with developmental delay, mild intellectual disability, hypotonia, and increased serum creatine kinase. Sanger sequencing was used to validate the variants identified in the siblings and their parents. In vitro functional study was performed. Results: A homozygous mutation, c.197G>A (p.Gly66Glu) in exon 4 of DPM2 (NM_003863) was identified by whole exome sequencing (WES). In vitro functional analysis demonstrated that this variant increased the expression level of DPM2 protein and western blot revealed a significant decrease in ICAM1, a universal biomarker for hypoglycosylation in patients with CDG, suggesting abnormal N-linked glycosylation. We also reviewed the 4 previously reported patients carrying homozygous or compound heterozygous variants of DMP2 gene, and found that patients with variants within the region encoding the first domain had more severe clinical symptoms than those with variants within the second domain. However, the actual genotype-phenotype relationship needs more study. Discussion: Overall, our study broadens the variant spectrum of DPM2 gene, attempts to explain the different phenotypes in patients with different DPM2 variants, and emphasizes the need of further functional studies to understand the underlying pathophysiology of the phenotypic heterogeneity.

The Ehlers–Danlos Syndromes against the Backdrop of Inborn Errors of Metabolism

The Ehlers–Danlos syndromes are a group of multisystemic heritable connective tissue disorders with clinical presentations that range from multiple congenital malformations, over adolescent-onset debilitating or even life-threatening complications of connective tissue fragility, to mild conditions that remain undiagnosed in adulthood. To date, thirteen different EDS types have been recognized, stemming from genetic defects in 20 different genes. While initial biochemical and molecular analyses mainly discovered defects in genes coding for the fibrillar collagens type I, III and V or their modifying enzymes, recent discoveries have linked EDS to defects in non-collagenous matrix glycoproteins, in proteoglycan biosynthesis and in the complement pathway. This genetic heterogeneity explains the important clinical heterogeneity among and within the different EDS types. Generalized joint hypermobility and skin hyperextensibility with cutaneous fragility, atrophic scarring and easy bruising are defining manifestations of EDS; however, other signs and symptoms of connective tissue fragility, such as complications of vascular and internal organ fragility, orocraniofacial abnormalities, neuromuscular involvement and ophthalmological complications are variably present in the different types of EDS. These features may help to differentiate between the different EDS types but also evoke a wide differential diagnosis, including different inborn errors of metabolism. In this narrative review, we will discuss the clinical presentation of EDS within the context of inborn errors of metabolism, give a brief overview of their underlying genetic defects and pathophysiological mechanisms and provide a guide for the diagnostic approach.

SRD5A3-CDG: Emerging Phenotypic Features of an Ultrarare CDG Subtype

Background: SRD5A3-CDG is a rare N-glycosylation defect caused by steroid 5 alpha reductase type 3 deficiency. Its key feature is an early severe visual impairment with variable ocular anomalies often leading to diagnosis. Additional symptoms are still poorly defined. In this case study, we discuss 11 genetically confirmed cases, and report on emerging features involving other systems in addition to the eye phenotype.

Methods: In total, 11 SRD5A3-CDG patients in five sets of sibships were included in the study. Data on 9 of 11 patients are as of yet unpublished. Patients’ results on biochemical and genetic investigations and on in-depth phenotyping are presented.

Results: Key diagnostic features of SRD5A3-CDG are ophthalmological abnormalities with early-onset retinal dystrophy and optic nerve hypoplasia. SRD5A3-CDG is also characterized by variable neurological symptoms including intellectual disability, ataxia, and hypotonia. Furthermore, ichthyosiform skin lesions, joint laxity, and scoliosis have been observed in our cohort. We also report additional findings including dystonia, anxiety disorder, gastrointestinal symptoms, and MRI findings of small basal ganglia and mal-rotated hippocampus, whereas previous publications described dysmorphic features as a common finding in SRD5A3, which could not be confirmed in our patient cohort.

Conclusion: The detailed description of the phenotype of this large cohort of patients with SRD5A3-CDG highlights that the key clinical diagnostic features of SRD5A3-CDG are an early onset form of ophthalmological problems in patients with a multisystem disorder with variable symptoms evolving over time. This should aid earlier diagnosis and confirms the need for long-time follow-up of patients.

Fatal Neonatal DOLK-CDG as a Rare Form of Syndromic Ichthyosis

Neonatal collodion baby or ichthyosis can pose a diagnostic challenge, and in many cases, only additional organ involvement or the course of the disease will help differentiate between non-syndromic and syndromic forms. Skin abnormalities are described in about 20% of the congenital disorders of glycosylation (CDG). Among those, some rare CDG forms constitute a special group among the syndromic ichthyoses and can initially misdirect the diagnosis towards non-syndromic genodermatosis. DOLK-CDG is such a rare subtype, resulting from a defect in dolichol kinase, in which the congenital skin phenotype (often ichthyosis) is later associated with variable extracutaneous features such as dilatative cardiomyopathy, epilepsy, microcephaly, visual impairment, and hypoglycemia and may lead to a fatal course. We report two neonatal cases of lethal ichthyosis from the same family, with distal digital constrictions and a progressive course leading to multi-organ failure and death. Postmortem trio whole-exome sequencing revealed the compound heterozygous variants NM_014908.3: c.1342G>A, p.(Gly448Arg) and NM_014908.3: c.1558A>G, p.(Thr520Ala) in the DOLK gene in the first affected child, which were confirmed in the affected sibling. Reduced staining with anti-α-Dystroglycan antibody was observed in frozen heart tissue of the second child as an expression of reduced O-mannosylation due to the dolichol kinase deficiency. In addition to the detailed dermatopathological changes, both cases presented hepatic and extrahepatic hemosiderosis on histological examination. Our patients represent an early and fatal form of DOLK-CDG with a striking presentation at birth resembling severe collodion baby. Both cases emphasize the phenotypic variability of glycosylation disorders and the importance to broaden the differential diagnosis of ichthyosis and to actively search for organ involvement in neonates with ichthyosis.

Genetic analysis and prenatal diagnosis in a Chinese with growth retardation, abnormal liver function, and microcephaly

Background

Congenital disorders of glycosylation (CDG) are a genetically heterogeneous group of disorders caused by defects in the synthesis and processing of glycoproteins. COG6‐CDG is a kind of disorder caused by conserved oligomeric golgi complex 6 (COG6) deficiency. To date, only 19 patients with COG6‐CDG have been reported.

Methods

We report a girl in a Chinese family with developmental delay, growth retardation, microcephaly, abnormal liver function, and hypohidrosis. Trio whole‐exome sequencing was performed for this patient and her parents, and the variants identified were validated by Sanger sequencing. Prenatal diagnosis was done for this family during a subsequent pregnancy. The literature review on these patients was performed by reviewing articles published in English and Chinese.

Results

Genetic sequencing identified two novel heterozygous mutations: c.428G>T (p.S143I) and c.1843C>T (p.Q615X) in the COG6 gene, inherited from her healthy parents, respectively. A total of 11 different mutations in COG6 have been reported previously, and mutations potentially affecting splicing are the most common. The main clinical features included development delay, facial dysmorphism, growth retardation, skin abnormalities (hypohidrosis), microcephaly, abnormal brain structure, liver involvement, and recurrent infections.

Conclusion

Our work broadens the mutation spectrum of COG6 gene and states the importance of whole‐exome sequencing in facilitating the definitive diagnosis of this disorder and prenatal diagnosis in a subsequent pregnancy.

Fructose and Mannose in Inborn Errors of Metabolism and Cancer

History suggests that tasteful properties of sugar have been domesticated as far back as 8000 BCE. With origins in New Guinea, the cultivation of sugar quickly spread over centuries of conquest and trade. The product, which quickly integrated into common foods and onto kitchen tables, is sucrose, which is made up of glucose and fructose dimers. While sugar is commonly associated with flavor, there is a myriad of biochemical properties that explain how sugars as biological molecules function in physiological contexts. Substantial research and reviews have been done on the role of glucose in disease. This review aims to describe the role of its isomers, fructose and mannose, in the context of inborn errors of metabolism and other metabolic diseases, such as cancer. While structurally similar, fructose and mannose give rise to very differing biochemical properties and understanding these differences will guide the development of more effective therapies for metabolic disease. We will discuss pathophysiology linked to perturbations in fructose and mannose metabolism, diagnostic tools, and treatment options of the diseases.

Expanding the phenotype of X-linked SSR4-CDG: Connective tissue implications

Signal sequence receptor protein 4 (SSR4) is a subunit of the translocon-associated protein complex, which participates in the translocation of proteins across the endoplasmic reticulum membrane, enhancing the efficiency of N-linked glycosylation. Pathogenic variants in SSR4 cause a congenital disorder of glycosylation: SSR4-congenital disorders of glycosylation (CDG). We describe three SSR4-CDG boys and review the previously reported. All subjects presented with hypotonia, failure to thrive, developmental delay, and dysmorphic traits and showed a type 1 serum sialotransferrin profile, facilitating the diagnosis. Genetic confirmation of this X-linked CDG revealed one de novo hemizygous deletion, one maternally inherited deletion, and one de novo nonsense mutation of SSR4. The present subjects highlight the similarities with a connective tissue disorder (redundant skin, joint laxity, blue sclerae, and vascular tortuosity). The connective tissue problems are relevant, and require preventive rehabilitation measures. As an X-linked disorder, genetic counseling is essential.

Transferrin isoelectric focusing for the investigation of congenital disorders of glycosylation: analysis of a ten-year experience in a Brazilian center

OBJECTIVES

To characterize cases of suspected congenital disorders of glycosylation (CDG) investigated in a laboratory in southern Brazil using the transferrin isoelectric focusing TfIEF test from 2008 to 2017.

METHOD

Observational, cross-sectional, retrospective study. The laboratory records of 1,546 individuals (median age=36 months, 25-75 IQR=10-108; males=810) submitted to the TfIEF test during the period were reviewed.

RESULTS

Fifty-one individuals (3%) had an altered TfIEF pattern (5±2.8 cases/year; median age=24 months, 25-75 IQR=11-57 months; males=27, 53%). For 14 of them, data on diagnosis conclusion were available (classic galactosemia=4; hereditary fructose intolerance=4; peroxisomal diseases=2; PMM2-CDG=2; MPDU1-CDG=1; SLC35A2-CDG=1).Comparing the cases with the normal and altered TfIEF patterns, there was a higher prevalence of altered cases in the age group from 11 months to 3 years. There was an increase in the likelihood of change in TfIEF, especially in the presence of inverted nipples or liver disease.

CONCLUSIONS

The data suggest that the investigation of a case with suspected CDG is a complex problem, being aggravated by the existence of other IEMs (inborn errors of metabolism) associated with altered TfIEF pattern and lack of access to confirmatory tests. The presence of inverted nipples and liver disease, especially in individuals aged 11 months to 3 years, should suggest the need for TfIEF investigation.

Neonatal presentation of COG6-CDG with prominent skin phenotype

Many of the genetic childhood disorders leading to death in the perinatal period follow autosomal recessive inheritance and bear specific challenges for genetic counseling and prenatal diagnostics. Often, affected children die before a genetic diagnosis can be established, thereby precluding targeted carrier testing in parents and prenatal or preimplantation genetic diagnosis in further pregnancies. The clinical phenotype of congenital disorders of glycosylation (CDG) is very heterogeneous and ranges from relatively mild symptoms to severe multisystem dysfunction and even a fatal course. A very rare subtype, COG6-CDG, is caused by deficiency of subunit 6 of the conserved oligomeric Golgi complex and is usually characterized by growth retardation, developmental delay, microcephaly, liver and gastrointestinal disease, joint contractures and episodic fever. It has been proposed that a distinctive feature of COG6-CDG can be ectodermal signs such as hypohidrosis/hyperthermia, hyperkeratosis and tooth anomalies. In a Greek family, who had lost two children in the neonatal period, with prominent skin features initially resembling restrictive dermopathy, severe arthrogryposis, respiratory insufficiency and a rapid fatal course trio whole-exome sequencing revealed the homozygous nonsense mutation c.511C>T, p.(Arg171*) in the COG6 gene. Skin manifestations such as dry skin and hyperkeratosis have been reported in only five out of the 21 reported COG6-CDG cases so far, including two patients with the c.511C>T variant in COG6 but with milder ectodermal symptoms. Our case adds to the phenotypic spectrum of COG6-CDG with prominent ectodermal manifestations at birth and underlines the importance of considering CDG among the possible causes for congenital syndromic genodermatoses.

The peroxisomal disorder spectrum and Heimler syndrome: Deep phenotyping and review of the literature

The spectrum of peroxisomal disorders is wide and comprises individuals that die in the first year of life, as well as people with sensorineural hearing loss, retinal dystrophy and amelogenesis imperfecta. In this article, we describe three patients; two diagnosed with Heimler syndrome and a third one with a mild-intermediate phenotype. We arrived at these diagnoses by conducting complete ophthalmic (National Eye Institute), auditory (National Institute of Deafness and Other Communication Disorders), and dental (National Institute of Dental and Craniofacial Research) evaluations, as well as laboratory and genetic testing. Retinal degeneration with macular cystic changes, amelogenesis imperfecta, and sensorineural hearing loss were features shared by the three patients. Patients A and C had pathogenic variants in PEX1 and Patient B, in PEX6. Besides analyzing these cases, we review the literature regarding mild peroxisomal disorders, their pathophysiology, genetics, differential diagnosis, diagnostic methods, and management. We suggest that peroxisomal disorders are considered in every child with sensorineural hearing loss and retinal degeneration. These patients should have a dental evaluation to rule out amelogenesis imperfecta as well as audiologic examination and laboratory testing including peroxisomal biomarkers and genetic testing. Appropriate diagnosis can lead to better genetic counseling and management of the associated comorbidities.

Genotypes and estimated prevalence of phosphomannomutase 2 deficiency in Turkey differ significantly from those in Europe

Phosphomannomutase 2 deficiency (PMM2-CDG) is an autosomal recessive congenital disorder of glycosylation, characterized by multisystem phenotypes, mostly including neurological involvement. In Turkey, due to high rates of consanguinity, many patients with autosomal recessive disorders have homozygous variants and these diseases are more common, compared to Europe. However, published reports of PMM2-CDG from Turkey are scarce. Here, we describe clinical and molecular characteristics of PMM2-CDG patients diagnosed in three centers in Turkey, using data obtained retrospectively from hospital records. We also analyzed an in-house exome database of 1,313 individuals for PMM2 variants and estimated allele, carrier and disease frequencies, using the Hardy-Weinberg law. Eleven patients were identified from 10 families, displaying similar characteristics to previous publications, with the exception of the first report of epilepsia partialis continua and increased prevalence of sensorineural hearing loss. p.Val231Met was the most common variant, and was homozygous in four patients. This novel genotype results in a neurological phenotype with subclinical visceral involvement. Exome database analysis showed an estimated prevalence of 1:286,726 for PMM2-CDG, which is much lower than expected (1:20,000 in Europe) because of the lack of predominance of the common European p.Asp141His allele, associated with a severe phenotype (allele frequency of 1:2,622 compared to 1:252 in gnomAD). These data suggest that prevalence, phenotypes and genotypes of PMM2-CDG in Turkey differ significantly from those in Europe: Milder phenotypes may be more common, but the disease itself rarer, requiring a higher clinical suspicion for diagnosis. The association of sensorineural hearing loss with PMM2-CDG warrants further study.

Congenital disorders of glycosylation

Congenital disorders of glycosylation are a genetically and clinically heterogeneous group of >130 diseases caused by defects in various steps along glycan modification pathways. The vast majority of these monogenic diseases are autosomal recessive and have multi-systemic manifestations, mainly growth failure, developmental delay, facial dysmorphisms, and variable coagulation and endocrine abnormalities. Carbohydrate deficient transferrin (CDT) and protein-linked glycan analysis with mass spectrometry can diagnose some subtypes of congenital disorders of glycosylation (CDG), while many currently rely on massively parallel genomic sequencing for diagnosis. Early detection is important, as a few of these disorders are treatable. Molecular and biochemical techniques continue to further our understanding of this rapidly expanding group of clinically and genetically diverse disorders.

From gestalt to gene: early predictive dysmorphic features of PMM2-CDG

Introduction

Phosphomannomutase-2 deficiency (PMM2-CDG) is associated with a recognisable facial pattern. There are no early severity predictors for this disorder and no phenotype–genotype correlation. We performed a detailed dysmorphology evaluation to describe facial gestalt and its changes over time, to train digital recognition facial analysis tools and to identify early severity predictors.

Methods

Paediatric PMM2-CDG patients were evaluated and compared with controls. A computer-assisted recognition tool was trained. Through the evaluation of dysmorphic features (DFs), a simple categorisation was created and correlated with clinical and neurological scores, and neuroimaging.

Results

Dysmorphology analysis of 31 patients (4–19 years of age) identified eight major DFs (strabismus, upslanted eyes, long fingers, lipodystrophy, wide mouth, inverted nipples, long philtrum and joint laxity) with predictive value using receiver operating characteristic (ROC) curveanalysis (p<0.001). Dysmorphology categorisation using lipodystrophy and inverted nipples was employed to divide patients into three groups that are correlated with global clinical and neurological scores, and neuroimaging (p=0.005, 0.003 and 0.002, respectively). After Face2Gene training, PMM2-CDG patients were correctly identified at different ages.

Conclusions

PMM2-CDG patients’ DFs are consistent and inform about clinical severity when no clear phenotype–genotype correlation is known. We propose a classification of DFs into major and minor with diagnostic risk implications. At present, Face2Gene is useful to suggest PMM2-CDG. Regarding the prognostic value of DFs, we elaborated a simple severity dysmorphology categorisation with predictive value, and we identified five major DFs associated with clinical severity. Both dysmorphology and digital analysis may help physicians to diagnose PMM2-CDG sooner.

Severe ichthyosis in MPDU1-CDG

Congenital disorders of glycosylation (CDG) have a broad spectrum of clinical manifestations. They can affect multiple organ systems, including skin and subcutaneous tissue. We report on an infant with severe ichthyosis caused by MPDU1 mutations. The case illustrates that skin manifestations are an important feature of CDG syndromes. Therefore, metabolic investigations should be included in the workup of infantile ichthyosis disorders.

Exome sequence identified a c.320A > G ALG13 variant in a female with infantile epileptic encephalopathy with normal glycosylation and random X inactivation: Review of the literature

Congenital Disorders of Glycosylation (CDG) are new and rapidly expanding neurometabolic disorders with multisystem involvements, broad phenotypic manifestations, and variable severity. The majority results from a defect of one of the steps involved with protein or lipid N-glycosylation pathway. Almost all are inherited in autosomal recessive patterns with a few exceptions such as the X-linked ALG13. Mutations of ALG13 are reported, so far in only 10 patients, all were ascertained through exome/genome sequencing. Specifically, the ALG13 c.320A > G (p.Asn107Ser) variant was reported only in females and in all were de novo mutations. These findings may suggest an X-linked dominant inheritance of this mutation with embryonic male lethality. These patients presented with severe infantile epileptic encephalopathy, global developmental delay, and multisystem abnormalities. Only two of these females had glycosylation studies done, and both showed normal pattern of glycosylated serum transferrin isoforms, and none had their X-chromosome inactivation patterns studied. Here, we report on another female patient who is heterozygous for the same ALG13 c.320A > G (p.Asn107Ser) variant. She presented with infantile spasms, epileptic encephalopathy, hypsarrhythmia, hypotonia, developmental delay, intellectual disability, abnormal coagulation profile, feeding problems, hypotonia, and dysmorphic features. The diagnosis of CGD was suspected clinically, but glycosylation studies were done twice and showed normal patterns on both occasions. Her X-inactivation study was also done and, surprisingly, showed a random pattern of X-inactivation, with no evidence of skewness.

What is new in CDG?

Congenital disorders of glycosylation (CDG) are one group among the disorders of glycosylation. The latter comprise defects associated with hypoglycosylation but also defects with hyperglycosylation. Genetic diseases with hypoglycosylation can be divided in primary congenital disorders of glycosylation (CDG) and in genetic diseases causing secondary hypoglycosylation. This review covers the human CDG highlights from the last 3 years (2014-2016) following a summary of the actual status of CDG. It expands on 23 novel CDG namely defects in SLC39A8, CAD, NANS, PGM3, SSR4, POGLUT1, NUS1, GANAB, PIGY, PIGW, PIGC, PIGG, PGAP1, PGAP3, VPS13B, CCDC115, TMEM199, ATP6AP1, ATP6V1A, ATP6V1E1, TRAPPC11, XYLT1 and XYLT2. Besides, it discusses novel phenotypes of known CDG (DHDDS-CDG, ALG9-CDG, EXT2-CDG, PIGA-CDG, PIGN-CDG), the elucidation of putative glycosyltransferase disorders as O-mannosylglycan synthesis disorders (TMEM5-CDG, ISPD-CDG, FKTN-CDG, FKRP-CDG), a novel CDG mechanism, advances in diagnosis, pathogenesis, treatment and finally an updated list of the 104 known CDG.

A Population-Based Study on Congenital Disorders of Protein N- and Combined with O-Glycosylation Experience in Clinical and Genetic Diagnosis

OBJECTIVE

To describe the clinical, biochemical, and genetic features of patients with congenital disorders of glycosylation (CDG) identified in Spain during the last 20 years.

STUDY DESIGN

Patients were selected among those presenting with multisystem disease of unknown etiology. The isoforms of transferrin and of ApoC3 and dolichols were analyzed in serum; phosphomannomutase and mannosephosphate isomerase activities were measured in fibroblasts. Conventional or massive parallel sequencing (customized panel or Illumina Clinical-Exome Sequencing TruSight One Gene Panel) was used to identify genes and mutations.

RESULTS

Ninety-seven patients were diagnosed with 18 different CDG. Eighty-nine patients had a type 1 transferrin profile; 8 patients had a type 2 transferrin profile, with 6 of them showing an alteration in the ApoC3 isoform profile. A total of 75% of the patients had PMM2-CDG presenting with a heterogeneous mutational spectrum. The remaining patients showed mutations in any of the following genes: MPI, PGM1, GFPT1, SRD5A3, DOLK, DPGAT1, ALG1, ALG6, RFT1, SSR4, B4GALT1, DPM1, COG6, COG7, COG8, ATP6V0A2, and CCDC115.

CONCLUSION

Based on literature and on this population-based study of CDG, a comprehensive scheme including reported clinical signs of CDG is offered, which will hopefully reduce the timeframe from clinical suspicion to genetic confirmation. The different defects of CDG identified in Spain have contributed to expand the knowledge of CDG worldwide. A predominance of PMM2 deficiency was detected, with 5 novel PMM2 mutations being described.

Immunological aspects of congenital disorders of glycosylation (CDG): a review

Congenital disorders of glycosylation (CDG) are a rapidly growing family of genetic diseases comprising more than 85 known distinct disorders. They show a great phenotypic variability ranging from multi-organ/system to mono-organ/system involvement with very mild to extremely severe expression. Immunological dysfunction has a significant impact on the phenotype in a minority of CDG. CDG with major immunological involvement are ALG12-CDG, MAGT1-CDG, MOGS-CDG, SLC35C1-CDG and PGM3-CDG. This review discusses the variety of immunological abnormalities reported in human CDG. Understanding the immunological aspects of CDG may contribute to a better management/treatment of these pathologies and possibly of more common diseases, such as inflammatory diseases.

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.