1
|
Rieger M, Türk M, Kraus C, Uebe S, Ekici AB, Krumbiegel M, Huchzermeyer C, Reis A, Thiel C. SRD5A3-CDG: Twins with an intragenic tandem duplication. Eur J Med Genet 2022; 65:104492. [PMID: 35339718 DOI: 10.1016/j.ejmg.2022.104492] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2022] [Revised: 03/15/2022] [Accepted: 03/20/2022] [Indexed: 11/03/2022]
Abstract
Steroid 5α-reductase type 3 congenital disorder of glycosylation (SRD5A3-CDG) is a rare metabolic disease mainly characterized by psychomotor disability, visual impairment, and variable eye malformations caused by bi-allelic pathogenic variants in SRD5A3. So far, only 23 distinct mutations were described. Exome sequencing in 32-year old monozygotic male twins revealed only the heterozygous splice variant c.562+3delG in SRD5A3, but no second variant. The twins presented with psychomotor deficit and a complex eye disease including retinal dystrophy, pallor of the papilla, nystagmus, and strabismus suggestive of SRD5A3-CDG. Only when applying exome-based copy number analysis, we identified as a second compound heterozygous variant a previously not reported tandem duplication of exons 2-4 in SRD5A3. Next to the typical skeletal anomalies of SRD5A3-CDG such as kyphosis and scoliosis, extension deficits of the proximal interphalangeal (PIP) joints IV were observed. Since similar contractures were described once in a patient with SRD5A3-CDG, we suggest that this rare symptom is possibly associated with SRD5A3-CDG. Our findings further expand the mutational and clinical spectrum of SRD5A3-CDG and emphasize the importance of an intragenic copy number analysis in patients with strong clinical suspicion of SRD5A3-CDG and only one detectable sequence variant.
Collapse
Affiliation(s)
- Melissa Rieger
- Institute of Human Genetics, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91054, Erlangen, Germany
| | - Matthias Türk
- Department of Neurology, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91054, Erlangen, Germany
| | - Cornelia Kraus
- Institute of Human Genetics, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91054, Erlangen, Germany
| | - Steffen Uebe
- Institute of Human Genetics, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91054, Erlangen, Germany
| | - Arif B Ekici
- Institute of Human Genetics, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91054, Erlangen, Germany
| | - Mandy Krumbiegel
- Institute of Human Genetics, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91054, Erlangen, Germany
| | - Cord Huchzermeyer
- Department of Ophthalmology, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91054, Erlangen, Germany
| | - André Reis
- Institute of Human Genetics, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91054, Erlangen, Germany
| | - Christian Thiel
- Institute of Human Genetics, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91054, Erlangen, Germany.
| |
Collapse
|
2
|
SRD5A3 defective congenital disorder of glycosylation: clinical utility gene card. Eur J Hum Genet 2020; 28:1297-1300. [PMID: 32424323 PMCID: PMC7609305 DOI: 10.1038/s41431-020-0647-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2019] [Accepted: 04/28/2020] [Indexed: 12/11/2022] Open
|
3
|
Gupta N, Verma G, Kabra M, Bijarnia-Mahay S, Ganapathy A. Identification of a case of SRD5A3-congenital disorder of glycosylation (CDG1Q) by exome sequencing. Indian J Med Res 2018; 147:422-426. [PMID: 29998879 PMCID: PMC6057243 DOI: 10.4103/ijmr.ijmr_820_16] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Affiliation(s)
- Neerja Gupta
- Department of Pediatrics, Division of Genetics, All India Institute of Medical Sciences, New Delhi, India
| | - Gaurav Verma
- Department of Pediatrics, Division of Genetics, All India Institute of Medical Sciences, New Delhi, India
| | - Madhulika Kabra
- Department of Pediatrics, Division of Genetics, All India Institute of Medical Sciences, New Delhi, India
| | | | | |
Collapse
|
4
|
Khan AO. Early-onset retinal dystrophy and chronic dermatitis in a girl with an undiagnosed congenital disorder of glycosylation (SRD5A3-CDG). Ophthalmic Genet 2018; 39:628-630. [DOI: 10.1080/13816810.2018.1498529] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Affiliation(s)
- Arif O. Khan
- Eye Institute, Cleveland Clinic Abu Dhabi, Abu Dhabi, United Arab Emirates
- Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine of Case Western University, Cleveland, Ohio
| |
Collapse
|
5
|
Wheeler PG, Ng BG, Sanford L, Sutton VR, Bartholomew DW, Pastore MT, Bamshad MJ, Kircher M, Buckingham KJ, Nickerson DA, Shendure J, Freeze HH. SRD5A3-CDG: Expanding the phenotype of a congenital disorder of glycosylation with emphasis on adult onset features. Am J Med Genet A 2016; 170:3165-3171. [PMID: 27480077 DOI: 10.1002/ajmg.a.37875] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Accepted: 07/08/2016] [Indexed: 12/15/2022]
Abstract
Increasing numbers of congenital disorders of glycosylation (CDG) have been reported recently resulting in an expansion of the phenotypes associated with this group of disorders. SRD5A3 codes for polyprenol reductase which converts polyprenol to dolichol. This is a major pathway for dolichol biosynthesis for N-glycosylation, O-mannosylation, C-mannosylation, and GPI anchor synthesis. We present the features of five individuals (three children and two adults) with mutations in SRD5A3 focusing on the variable eye and skin involvement. We compare that to 13 affected individuals from the literature including five adults allowing us to delineate the features that may develop over time with this disorder including kyphosis, retinitis pigmentosa, and cataracts. © 2016 Wiley Periodicals, Inc.
Collapse
Affiliation(s)
| | - Bobby G Ng
- Human Genetics Program, Sanford-Burnham Prebys Medical Discovery Institute, La Jolla, California
| | | | - V Reid Sutton
- Department of Molecular and Human Genetics, Baylor College of Medicine and Texas Children's Hospital, Houston, Texas
| | - Dennis W Bartholomew
- Section of Molecular and Human Genetics, Nationwide Children's Hospital, Department of Pediatrics, Ohio State University, Columbus, Ohio
| | - Matthew T Pastore
- Section of Molecular and Human Genetics, Nationwide Children's Hospital, Department of Pediatrics, Ohio State University, Columbus, Ohio
| | - Michael J Bamshad
- Department of Genome Sciences, University of Washington Center for Mendelian Genomics, University of Washington, Seattle, Washington.,Department of Pediatrics, University of Washington, Seattle, Washington
| | - Martin Kircher
- Department of Pediatrics, University of Washington, Seattle, Washington
| | - Kati J Buckingham
- Department of Pediatrics, University of Washington, Seattle, Washington
| | - Deborah A Nickerson
- Department of Genome Sciences, University of Washington Center for Mendelian Genomics, University of Washington, Seattle, Washington
| | - Jay Shendure
- Department of Genome Sciences, University of Washington Center for Mendelian Genomics, University of Washington, Seattle, Washington.,Howard Hughes Medical Institute, University of Washington, Seattle, Washington
| | - Hudson H Freeze
- Human Genetics Program, Sanford-Burnham Prebys Medical Discovery Institute, La Jolla, California
| |
Collapse
|
6
|
Abstract
We present a boy, admitted at 4 months, with facial dysmorphism, hypertrichosis, loose skin, bilateral inguinal hernia, severe hypotonia, psychomotor disability, seizures with hypsarrhythmia (West syndrome), hepatosplenomegaly, increased serum transaminases, iris coloboma, glaucoma, corneal clouding and bilateral dilated lateral ventricles, and extra-axial post-cerebellar space. Serum transferrin isoelectrofocusing (IEF) showed a type 1 pattern. Whole-exome genotyping showed a previously reported homozygous nonsense mutation c.320G>A; p.Trp107X in SRD5A3. Epilepsy and glaucoma have been reported only once in the 19 described SRD5A3-congenital glycosylation defect patients, and corneal clouding not at all.
Collapse
|
7
|
Kara B, Ayhan Ö, Gökçay G, Başboğaoğlu N, Tolun A. Adult phenotype and further phenotypic variability in SRD5A3-CDG. BMC MEDICAL GENETICS 2014; 15:10. [PMID: 24433453 PMCID: PMC3898029 DOI: 10.1186/1471-2350-15-10] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/12/2013] [Accepted: 01/08/2014] [Indexed: 12/22/2022]
Abstract
Background SRD5A3 is responsible for SRD5A3-CDG, a type of congenital disorder of glycosylation, and mutations have been reported in 15 children. All the mutations are recessive and truncating. Case presentation We present 2 brothers at the age of 38 and 40 years with an initial diagnosis of cerebellar ataxia. We found the candidate disease loci via linkage analysis using data from single nucleotide polymorphism genome scans and homozygous truncating mutation SRD5A3 p.W19X, which was previously reported in 3 unrelated children, by exome sequencing. Clinical investigations included physical and ocular examinations and blood tests. Severe ocular involvement with retinal bone spicule pigmentation and optic atrophy are the most prominent disabling clinical features of the disease. The serum transferrin isoelectric focusing (TIEF) pattern is abnormal in the patient investigated. Conclusion Our patients are older, with later onset and milder clinical phenotypes than all patients with SRD5A3-CDG reported so far. They also have atypical ocular findings and variable phenotypes. Our findings widen the spectrum of phenotypes resulting from SRD5A3 mutations and the clinical variability of SRD5A3-CDG, and suggest screening for SRD5A3 mutations in new patients with at least a few of the clinical symptoms of SRD5A3-CDG.
Collapse
Affiliation(s)
| | | | | | | | - Aslıhan Tolun
- Department of Molecular Biology and Genetics, Boğaziçi University, Istanbul, Turkey.
| |
Collapse
|
8
|
Gründahl J, Guan Z, Rust S, Reunert J, Müller B, Du Chesne I, Zerres K, Rudnik-Schöneborn S, Ortiz-Brüchle N, Häusler M, Siedlecka J, Swiezewska E, Raetz C, Marquardt T. Life with too much polyprenol: polyprenol reductase deficiency. Mol Genet Metab 2012; 105:642-51. [PMID: 22304929 PMCID: PMC3428379 DOI: 10.1016/j.ymgme.2011.12.017] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/05/2011] [Revised: 12/20/2011] [Accepted: 12/20/2011] [Indexed: 11/27/2022]
Abstract
Congenital disorders of glycosylation (CDG) are caused by a dysfunction of glycosylation, an essential step in the manufacturing process of glycoproteins. This paper focuses on a 6-year-old patient with a new type of CDG-I caused by a defect of the steroid 5α reductase type 3 gene (SRD5A3). The clinical features were psychomotor retardation, pathological nystagmus, slight muscular hypotonia and microcephaly. SRD5A3 was recently identified encoding the polyprenol reductase, an enzyme catalyzing the final step of the biosynthesis of dolichol, which is required for the assembly of the glycans needed for N-glycosylation. Although an early homozygous stop-codon (c.57G>A [W19X]) with no functional protein was found in the patient, about 70% of transferrin (Tf) was correctly glycosylated. Quantification of dolichol and unreduced polyprenol in the patient's fibroblasts demonstrated a high polyprenol/dolichol ratio with normal amounts of dolichol, indicating that high polyprenol levels might compete with dolichol for the initiation of N-glycan assembly but without supporting normal glycosylation and that there must be an alternative pathway for dolichol biosynthesis.
Collapse
Affiliation(s)
- J.E.H. Gründahl
- Universitätsklinikum Münster, Klinik und Poliklinik für Kinder- und Jugendmedizin—Allgemeine Pädiatrie, Münster, Germany
| | - Z. Guan
- Department of Biochemistry, Duke University Medical Center, Durham, NC, USA
| | - S. Rust
- Leibniz-Institut für Arterioskleroseforschung, Münster, Germany
| | - J. Reunert
- Universitätsklinikum Münster, Klinik und Poliklinik für Kinder- und Jugendmedizin—Allgemeine Pädiatrie, Münster, Germany
| | - B. Müller
- Department of Pediatrics, University Hospital RWTH Aachen, Germany
| | - I. Du Chesne
- Universitätsklinikum Münster, Klinik und Poliklinik für Kinder- und Jugendmedizin—Allgemeine Pädiatrie, Münster, Germany
| | - K. Zerres
- Institute of Human Genetics, University Hospital RWTH Aachen, Germany
| | | | - N. Ortiz-Brüchle
- Institute of Human Genetics, University Hospital RWTH Aachen, Germany
| | - M.G. Häusler
- Department of Pediatrics, University Hospital RWTH Aachen, Germany
| | - J. Siedlecka
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
| | - E. Swiezewska
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
| | - C.R.H. Raetz
- Department of Biochemistry, Duke University Medical Center, Durham, NC, USA
| | - T. Marquardt
- Universitätsklinikum Münster, Klinik und Poliklinik für Kinder- und Jugendmedizin—Allgemeine Pädiatrie, Münster, Germany
- Corresponding author at: Klinik für Kinder- und Jugendmedizin, Albert-Schweitzer-Str. 33, 48149 Münster, Germany. Fax: +49 251 835 6085. (T. Marquardt)
| |
Collapse
|
9
|
Morava E, Wevers RA, Cantagrel V, Hoefsloot LH, Al-Gazali L, Schoots J, van Rooij A, Huijben K, van Ravenswaaij-Arts CMA, Jongmans MCJ, Sykut-Cegielska J, Hoffmann GF, Bluemel P, Adamowicz M, van Reeuwijk J, Ng BG, Bergman JEH, van Bokhoven H, Körner C, Babovic-Vuksanovic D, Willemsen MA, Gleeson JG, Lehle L, de Brouwer APM, Lefeber DJ. A novel cerebello-ocular syndrome with abnormal glycosylation due to abnormalities in dolichol metabolism. ACTA ACUST UNITED AC 2010; 133:3210-20. [PMID: 20852264 DOI: 10.1093/brain/awq261] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Cerebellar hypoplasia and slowly progressive ophthalmological symptoms are common features in patients with congenital disorders of glycosylation type I. In a group of patients with congenital disorders of glycosylation type I with unknown aetiology, we have previously described a distinct phenotype with severe, early visual impairment and variable eye malformations, including optic nerve hypoplasia, retinal coloboma, congenital cataract and glaucoma. Some of the symptoms overlapped with the phenotype in other congenital disorders of glycosylation type I subtypes, such as vermis hypoplasia, anaemia, ichtyosiform dermatitis, liver dysfunction and coagulation abnormalities. We recently identified pathogenic mutations in the SRD5A3 gene, encoding steroid 5α-reductase type 3, in a group of patients who presented with this particular phenotype and a common metabolic pattern. Here, we report on the clinical, genetic and metabolic features of 12 patients from nine families with cerebellar ataxia and congenital eye malformations diagnosed with SRD5A3-congenital disorders of glycosylation due to steroid 5α-reductase type 3 defect. This enzyme is necessary for the reduction of polyprenol to dolichol, the lipid anchor for N-glycosylation in the endoplasmic reticulum. Dolichol synthesis is an essential metabolic step in protein glycosylation. The current defect leads to a severely abnormal glycosylation state already in the early phase of the N-glycan biosynthesis pathway in the endoplasmic reticulum. We detected high expression of SRD5A3 in foetal brain tissue, especially in the cerebellum, consistent with the finding of the congenital cerebellar malformations. Based on the overlapping clinical, biochemical and genetic data in this large group of patients with congenital disorders of glycosylation, we define a novel syndrome of cerebellar ataxia associated with congenital eye malformations due to a defect in dolichol metabolism.
Collapse
Affiliation(s)
- Eva Morava
- Radboud University Nijmegen Medical Centre, Institute for Genetic and Metabolic Disease, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
10
|
Vleugels W, Schollen E, Foulquier F, Matthijs G. Screening for OST deficiencies in unsolved CDG-I patients. Biochem Biophys Res Commun 2009; 390:769-74. [PMID: 19835842 DOI: 10.1016/j.bbrc.2009.10.047] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2009] [Accepted: 10/09/2009] [Indexed: 10/20/2022]
Abstract
Congenital Disorders of Glycosylation (CDG) are a group of inherited disorders caused by deficiencies in glycosylation. Since 1980, 14 CDG type I (CDG-I) defects have been identified in the endoplasmic reticulum, all affecting the assembly of the oligosaccharide precursor. However, the number of unsolved CDG-I (CDG-Ix) patients displaying protein hypoglycosylation in combination with an apparently normal assembly of the oligosaccharide precursor is currently expanding. We hypothesized that the hypoglycosylation observed in some of these patients could be caused by a deficiency in the transfer of the oligosaccharide precursor onto protein, a reaction catalyzed by the oligosaccharyltransferase (OST) complex. For this purpose, the different subunits of the OST complex were screened in 27 CDG-Ix patients for whom structural analysis of the lipid-linked oligosaccharides revealed a normal level and intact structure of the oligosaccharide precursor. Among these 27 patients, one was identified with a homozygous missense mutation (c.1121G>A; p.G374D) in the ribophorin 2 (RPN2) subunit of the OST complex. The pathogenic nature of this mutation remains unproven due to the complexity of tackling a possible OST defect.
Collapse
Affiliation(s)
- Wendy Vleugels
- Laboratory for Molecular Diagnosis, Center for Human Genetics, University of Leuven, B-3000 Leuven, Belgium
| | | | | | | |
Collapse
|
11
|
Morava E, Wosik H, Kárteszi J, Guillard M, Adamowicz M, Sykut-Cegielska J, Hadzsiev K, Wevers RA, Lefeber DJ. Congenital disorder of glycosylation type Ix: review of clinical spectrum and diagnostic steps. J Inherit Metab Dis 2008; 31:450-6. [PMID: 18500572 DOI: 10.1007/s10545-008-0822-0] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/26/2007] [Revised: 02/01/2008] [Accepted: 02/20/2008] [Indexed: 10/22/2022]
Abstract
Congenital disorder of glycosylation type I (CDG I) represent a rapidly growing group of inherited multisystem disorders with 13 genetically established subtypes (CDG Ia to CDG Im), and a high number of biochemically unresolved cases (CDG Ix). Further diagnostic effort and prognosis counselling are very challenging in these children. In the current study, we reviewed the clinical records of 10 CDG Ix patients and compared the data with 13 CDG Ix patients published in the literature in search for specific symptoms to create clinical subgroups. The most frequent findings were rather nonspecific, including developmental delay and axial hypotonia. Several features were found that are uncommon in CDG syndrome, such as elevated creatine kinase or arthrogryposis. Distinct ophthalmological abnormalities were observed including optic nerve atrophy, cataract and glaucoma. Two subgroups could be established: one with a pure neurological presentation and the other with a neurological-multivisceral form. The first group had a significantly better prognosis. The unique presentation of microcephaly, seizures, ascites, hepatomegaly, nephrotic syndrome and severe developmental delay was observed in one child diagnosed with CDG Ik. Establishing clinical subgroups and increasing the number of patients within the subgroups may lead the way towards the genetic defect in children with a so far unsolved type of the congenital disorders of glycosylation. Raising awareness for less common, non-CDG specific clinical features such as congenital joint contractures, movement disorders or ophthalmological anomalies will encourage clinicians to think of CDG in its more unusual presentation. Clinical grouping also helps to determine the prognosis and provide better counselling for the families.
Collapse
Affiliation(s)
- E Morava
- Laboratory of Paediatrics and Neurology, Department of Paediatrics, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
| | | | | | | | | | | | | | | | | |
Collapse
|
12
|
Abstract
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.
Collapse
Affiliation(s)
- Jaak Jaeken
- Department of Pediatrics, Center for Metabolic Disease, University of Leuven, Leuven, Belgium.
| | | |
Collapse
|
13
|
Abstract
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.
Collapse
Affiliation(s)
- Marc C Patterson
- Division of Pediatric Neurology, Columbia University Medical Center, Harkness Pavilion, HP-540, 180 Fort Washington Avenue, New York, NY 10032, USA
| |
Collapse
|
14
|
Abstract
Congenital disorders of glycosylation (CDGs) are due to defects in the synthesis of the glycan moiety of glycoproteins or other glycoconjugates. This review is devoted mainly to the clinical aspects of protein glycosylation defects. There are two main types of protein glycosylation: N-glycosylation and O-glycosylation. N-glycosylation generally consists of an assembly pathway (in cytosol and endoplasmic reticulum) and a processing pathway (in endoplasmic reticulum and Golgi). O-glycosylation lacks a processing pathway but is otherwise more complex. Sixteen disease-causing defects are known in protein glycosylation: 12 in N-glycosylation and four in O-glycosylation. The N-glycosylation defects comprise eight assembly defects (CDG-I) designated CDG-Ia to CDG-Ih, and four processing defects (CDG-II) designated CDG-IIa to CDG-IId. By far the most frequent is CDG-Ia (phosphomannomutase-2 deficiency). It affects the nervous system and many other organs. Its clinical expression varies from extremely severe to very mild (and thus probably underdiagnosed). The most interesting disease in this group is CDG-Ib (phosphomannose isomerase deficiency) because it is so far the only efficiently treatable CDG (mannose treatment). It has a hepatic-intestinal presentation. The O-glycosylation defects comprise two O-xylosylglycan defects (a progeroid variant of Ehlers-Danlos syndrome and the multiple exostoses syndrome) and two O-mannosylglycan defects (Walker-Warburg syndrome and muscle-eye-brain disease). All known CDGs have a recessive inheritance except for multiple exostoses syndrome, which is dominantly inherited. There is a rapidly growing group of putative CDGs with a large spectrum of clinical presentations (CDG-x). Serum transferrin iso-electrofocusing remains the cornerstone of the screening for N-glycosylation defects associated with sialic acid deficiency. Abnormal patterns can be grouped in to type 1 and type 2. However, a normal pattern does not exclude these defects. Screening for the other CDGs is much more difficult, particularly when the defect is organ- or system-restricted. The latter group promises to become an important new chapter in CDG. It is concluded that CDGs will eventually cover the whole clinical spectrum of paediatric and adult disease manifestations.
Collapse
Affiliation(s)
- J Jaeken
- Department of Pediatrics, Centre for Metabolic Disease, University Hospital Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium.
| |
Collapse
|