Congenital disorder of glycosylation

Congenital disorders of glycosylation
Classification and external resources
ICD-10 E77.8
ICD-9 271.8
OMIM 212065 212066
DiseasesDB 2012 31730

A congenital disorder of glycosylation (previously called carbohydrate-deficient glycoprotein syndrome) is one of several rare inborn errors of metabolism in which glycosylation of a variety of tissue proteins and/or lipids is deficient or defective. Congenital disorders of glycosylation are sometimes known as CDG syndromes. They often cause serious, sometimes fatal, malfunction of several different organ systems (especially the nervous system, muscles, and intestines) in affected infants. The most common subtype is CDG-Ia (also referred to as PMM2-CDG) where the genetic defect leads to the loss of phosphomannomutase 2, the enzyme responsible for the conversion of mannose-6-phosphate into mannose-1-phosphate.

History

The first CDG patients (twin sisters) were described in an abstract in the medical journal Pediatric Research in 1980 by Jaeken et al. [1] Their main features were psychomotor retardation, cerebral and cerebellar atrophy and fluctuating hormone levels (e.g.prolactin, FSH and GH). During the next 15 years the underlying defect remained unknown but since the plasmaprotein transferrin was underglycosylated (as shown by e.g. isoelectric focusing), the new syndrome was named carbohydrate-deficient glycoprotein syndrome (CDGS).[2] Its "classical" phenotype included psychomotor retardation, ataxia, strabismus, anomalies (fat pads and inverted nipples) and coagulopathy.

In 1994, a new phenotype was described and named CDGS-II.[3] In 1995, Van Schaftingen and Jaeken showed that CDGS-I (now CDG-Ia or PMM2-CDG) was caused by the deficiency of the enzyme phosphomannomutase. This enzyme is responsible for the interconversion of mannose-6-phosphate and mannose-1-phosphate, and its deficiency leads to a shortage in GDP-mannose and dolichol (Dol)-mannose (Man), two donors required for the synthesis of the lipid-linked oligosaccharide precursor of N-linked glycosylation.

In 1998, Niehues et al. published a new CDG syndrome, CDG-Ib, which is caused by mutations in the enzyme metabolically upstream of PMM2, phosphomannose isomerase (PMI).[4] In this paper, the authors also described a functional therapy for CDG-Ib, alimentary mannose.

The characterization of new defects took up speed and several new Type I and Type II defects were delineated.[5]

In 2012, Need et al. published the first case of a congenital disorder of deglycosylation, which resulted from mutations in the NGLY1 gene.[6] A 2014 study of NGLY1 deficient patients found similarities with traditional congenital disorders of glycosylation.[7]

Classification

Historically, CDGs are classified as Types I and II (CDG-I and CDG-II), depending on the nature and location of the biochemical defect in the metabolic pathway relative to the action of oligosaccharyltransferase. The most commonly used screening method for CDG, analysis of transferrin glycosylation status by isoelectric focusing, ESI-MS, or other techniques, distinguish between these subtypes in so called Type I and Type II patterns.

Currently, twenty-two CDG Type-I and fourteen Type-II subtypes of CDG have been described.[8]

Since 2009, most researchers use a different nomenclature based on the gene defect (e.g. CDG-Ia = PMM2-CDG, CDG-Ib = PMI-CDG, CDG-Ic = ALG6-CDG etc.).[9] The reason for the new nomenclature was the fact that proteins not directly involved in glycan synthesis (such as members of the COG-family[10] and vesicular H+-ATPase [11]) were found to be causing the glycosylation defect in some CDG patients.

Also, defects disturbing other glycosylation pathways than the N-linked one are included in this classification. Examples are the α-dystroglycanopathies (e.g. POMT1/POMT2-CDG (Walker-Warburg syndrome and Muscle-Eye-Brain syndrome)) with deficiencies in O-mannosylation of proteins; O-xylosylglycan synthesis defects (EXT1/EXT2-CDG (hereditary multiple exostoses) and B4GALT7-CDG (Ehlers-Danlos syndrome, progeroid variant)); O-fucosylglycan synthesis (B3GALTL-CDG (Peter’s plus syndrome) and LFNG-CDG (spondylocostal dysostosis III)).

Type I

Types include:

Type OMIM Gene Locus
Ia (PMM2-CDG) 212065 PMM2 16p13.3-p13.2
Ib (MPI-CDG) 602579 MPI 15q22-qter
Ic (ALG6-CDG) 603147 ALG6 1p22.3
Id (ALG3-CDG) 601110 ALG3 3q27
Ie (DPM1-CDG) 608799 DPM1 20q13.13
If (MPDU1-CDG) 609180 MPDU1 17p13.1-p12
Ig (ALG12-CDG) 607143 ALG12 22q13.33
Ih (ALG8-CDG) 608104 ALG8 11pter-p15.5
Ii (ALG2-CDG) 607906 ALG2 9q22
Ij (DPAGT1-CDG) 608093 DPAGT1 11q23.3
Ik (ALG1-CDG) 608540 ALG1 16p13.3
1L (ALG9-CDG) 608776 ALG9 11q23
Im (DOLK-CDG) 610768 DOLK 9q34.11
In (RFT1-CDG) 612015 RFT1 3p21.1
Io (DPM3-CDG) 612937 DPM3 1q12-q21
Ip (ALG11-CDG) 613661 ALG11 13q14.3
Iq (SRD5A3-CDG) 612379 SRD5A3 4q12
Ir (DDOST-CDG) 614507 DDOST 1p36.12
DPM2-CDG n/a DPM2 9q34.13
TUSC3-CDG 611093 TUSC3 8p22
MAGT1-CDG 300716 MAGT1 X21.1
DHDDS-CDG 613861 DHDDS 1p36.11
I/IIx 212067 n/a n/a

Type II

Types include:

Type OMIM Gene Locus
IIa (MGAT2-CDG) 212066 MGAT2 14q21
IIb (GCS1-CDG) 606056 GCS1 2p13-p12
IIc (SLC335C1-CDG; Leukocyte adhesion deficiency II)) 266265 SLC35C1 11p11.2
IId (B4GALT1-CDG) 607091 B4GALT1 9p13
IIe (COG7-CDG) 608779 COG7 16p
IIf (SLC35A1-CDG) 603585 SLC35A1 6q15
IIg (COG1-CDG) 611209 COG1 17q25.1
IIh (COG8-CDG) 611182 COG8 16q22.1
IIi (COG5-CDG) 613612 COG5 7q31
IIj (COG4-CDG) 613489 COG4 16q22.1
IIL (COG6-CDG) n/a COG6 13q14.11
ATP6V0A2-CDG (autosomal recessive cutis laxa type 2a (ARCL-2A)) 219200 ATP6V0A2 12q24.31
MAN1B1-CDG (Mental retardation, autosomal recessive 15) 614202 MAN1B1 9q34.3
ST3GAL3-CDG (Mental retardation, autosomal recessive 12) 611090 ST3GAL3 1p34.1

Disorders of O-mannosylation

Mutations in several genes have been associated with the traditional clinical syndromes, termed muscular dystrophy-dystroglycanopathies (MDDG). A new nomenclature based on clinical severity and genetic cause was recently proposed by OMIM.[12] The severity classifications are A (severe), B (intermediate), and C (mild). The subtypes are numbered one to six according to the genetic cause, in the following order: (1) POMT1, (2) POMT2, (3) POMGNT1, (4) FKTN, (5) FKRP, and (6) LARGE.

Most common severe types include:

Name OMIM Gene Locus
POMT1-CDG (MDDGA1;Walker-Warburg syndrome) 236670 POMT1 9q34.13
POMT2-CDG (MDDGA2;Walker-Warburg syndrome) 613150 POMT2 14q24.3
POMGNT1-CDG (MDDGA3; muscle-eye-brain) 253280 POMGNT1 1p34.1
FKTN-CDG (MDDGA4; Fukuyama congenital muscular dystrophy) 253800 FKTN 9q31.2
FKRP-CDG (MDDGB5; MDC1C) 606612 FKRP 19q13.32
LARGE-CDG (MDDGB6; MDC1D) 608840 LARGE 22q12.3

Presentation

The specific problems produced differ according to the particular abnormal synthesis involved. Common manifestations include ataxia; seizures; retinopathy; liver fibrosis; coagulopathies; failure to thrive; dysmorphic features (e.g., inverted nipples and subcutaneous fat pads; and strabismus. If an MRI is obtained, cerebellar atrophy and hypoplasia is a common finding.

Ocular abnormalities of CDG-Ia include: myopia, infantile esotropia, delayed visual maturation, low vision, optic disc pallor, and reduced rod function on electroretinography.[13]

Three subtypes of CDG I (a,b,d) can cause congenital hyperinsulinism with hyperinsulinemic hypoglycemia in infancy.[14]

N-Glycosylation and known defects

A biologically very important group of carbohydrates is the asparagine (Asn)-linked, or N-linked, oligosaccharides. Their biosynthetic pathway is very complex and involves a hundred or more glycosyltransferases, glycosidases, transporters and synthases. This plethora allows for the formation of a multitude of different final oligosaccharide structures, involved in protein folding, intracellular transport/localization, protein activity, and degradation/half-life. A vast amount of carbohydrate binding molecules (lectins) depend on correct glycosylation for appropriate binding; the selectins, involved in leukocyte extravasation, is a prime example. Their binding depends on a correct fucosylation of cell surface glycoproteins. Lack thereof leads to leukocytosis and increase sensitivity to infections as seen in SLC35C1-CDG(CDG-IIc); caused by a GDP-fucose (Fuc) transporter deficiency.

All N-linked oligosaccharides originate from a common lipid-linked oligosaccharide (LLO) precursor, synthesized in the ER on a dolichol-phosphate (Dol-P) anchor. The mature LLO is transferred co-translationally to consensus sequence Asn residues in the nascent protein, and is further modified by trimming and re-building in the Golgi.

Deficiencies in the genes involved in N-linked glycosylation constitute the molecular background to most of the CDGs.

Type I

Description Disorder Product
The formation of the LLO is initiated by the synthesis of the polyisoprenyl dolichol from farnesyl, a precursor of cholesterol biosynthesis. This step involves at least three genes, DHDDS (encoding dehydrodolichyl diphosphate synthase that is a cis-prenyl transferase), DOLPP1 (a pyrophosphatase) and SRD5A3, encoding a reductase that completes the formation of dolichol. Recently, exome sequencing showed that mutations in DHDDS cause a disorder with a retinal phenotype (retinitis pigmentosa, a common finding in CDG patients.[15] Further, the intermediary reductase in this process (encoded by SRD5A3), is deficient in SRD5A3-CDG (CDG-Iq).[16]
Dol is then activated to Dol-P via the action of Dol kinase in the ER membrane. This process is defective in DOLK-CDG (CDG-Im).[17]
Consecutive N-acetylglucosamine (GlcNAc)- and mannosyltransferases use the nucleotide sugar donors UDP-GlcNAc and GDP-mannose (Man) to form a pyrophosphate-linked seven sugar glycan structure (Man5GlcNAc2-PP-Dol) on the cytoplasmatic side of the ER. Some of these steps have been found deficient in patients.
  • Deficiency in GlcNAc-1-P transferase causes DPAGT1-CDG (CDG-Ij)[18]
  • Loss of the first mannosyltransferase causes ALG1-CDG (CDG-Ik)[19]
  • Loss of the second mannosyltransferase (adds Man II and III) causes ALG2-CDG (CDG-Ii).[20]
  • Loss of the third mannosyltransferase (adds Man IV and V) causes ALG11-CDG (CDG-Ip)[21]
  • Mutations in the other genes involved in these steps (ALG13 and ALG14) are yet to be described.
 Man5GlcNAc2-PP-Dol
The M5GlcNAc2-structure is then flipped to the ER lumen, via the action of a "flippase" This is deficient in RFT1-CDG (CDG-In).[22]
Finally, three mannosyltransferases and three glucosyltransferases complete the LLO structure Glc3Man9GlcNAc2-PP-Dol using Dol-P-Man and Dol-P-glucose (Glc) as donors. There are five known defects:
  • mannosyltransferase VI deficiency causes ALG3-CDG (CDG-Id)[23]
  • mannosyltransferase VII/IX deficiency causes ALG9-CDG (CDG-IL)[24]
  • mannosyltransferase VIII deficiency causes ALG12-CDG (CDG-Ig)[25]
  • glucosyltransferase I deficiency causes ALG6-CDG (CDG-Ic)[26]
  • glucosyltransferase II deficiency causes ALG8-CDG (CDG-Ih).[27]
 Glc3Man9GlcNAc2-PP-Dol
A protein with hitherto unknown activity, MPDU-1, is required for the efficient presentation of Dol-P-Man and Dol-P-Glc. Its deficiency causes MPDU1-CDG (CDG-If).[28]
The synthesis of GDP-Man is crucial for proper N-glycosylation, as it serves as donor substrate for the formation of Dol-P-Man and the initial Man5GlcNAc2-P-Dol structure. GDP-Man synthesis is linked to glycolysis via the interconversion of fructose-6-P and Man-6-P, catalyzed by phosphomannose isomerase (PMI). This step is deficient in MPI-CDG (CDG-Ib),[29] which is the only treatable CDG-I subtype.
Man-1-P is then formed from Man-6-P, catalyzed by phosphomannomutase (PMM2), and Man-1-P serves as substrate in the GDP-Man synthesis. Mutations in PMM2 cause PMM2-CDG (CDG-Ia), the most common CDG subtype.[30]
Dol-P-Man is formed via the action of Dol-P-Man synthase, consisting of three subunits; DPM1, DPM2, and DPM3. Mutations in DPM1 causes DPM1-CDG (CDG-Ie). Interestingly, mutations in DPM2 (DPM2-CDG) and DPM3 (DPM3-CDG (CDG-Io))[31] cause syndromes with a muscle phenotype resembling an a-dystroglycanopathy, possibly due to lack of Dol-P-Man required for O-mannosylation.
The final Dol-PP-bound 14mer oligosaccharides (Glc3Man9GlcNAc2-PP-Dol) are transferred to consensus Asn residues in the acceptor proteins in the ER lumen, catalyzed by the oligosaccharyltransferase(OST). The OST is composed by several subunits, including DDOST, TUSC3, MAGT1, KRTCAP2 and STT3a and -3b. Three of these genes have hithero been shown to be mutated in CDG patients, DDOST (DDOST-CDG (CDG-Ir)), TUSC3 (TUSC3-CDG) and MAGT1 (MAGT1-CDG).

Type II

The mature LLO chain is next transferred to the growing protein chain, a process catalysed by the oligosaccharyl transferase (OST) complex.

Not all structures are fully modified, some remain as high-mannose structures, others as hybrids (one unmodified Man branch and one modified), but the majority become fully modified complex type oligosaccharides.

In addition to glycosidase I, mutations have been found:

However, the use of >100 genes in this process, presumably means that many more defects are to be found.

Treatment

No treatment is available for most of these disorders. Mannose supplementation relieves the symptoms in PMI-CDG (CDG-Ib) for the most part,[32] even though the hepatic fibrosis may persist.[33] Fucose supplementation has had a partial effect on some SLC35C1-CDG (CDG-IIc or LAD-II) patients.[34]

See also

References

  1. ↑ Jaeken, J., Vanderschueren-Lodeweyckx, M., Casaer, P., Snoeck, L., Corbeel, L., Eggermont, E., and Eeckels, R. (1980) Pediatr Res 14, 179
  2. ↑ Jaeken, J., and Carchon, H. (1993) The carbohydrate-deficient glycoprotein syndromes: an overview. J Inherit Metab Dis. 16, 813-20.
  3. ↑ Jaeken, J., Schachter, H., Carchon, H., De Cock, P., Coddeville, B. and Spik, G. (1994) Arch. Dis. Childhood 71, 123-127
  4. ↑ Niehues, R., Hasilik, M., Alton, G., Körner, C., Schiebe-Sukumar, M., Koch, H.G., Zimmer, K.P., Wu, R., Harms, E., Reiter, K., von Figura, K., Freeze, H.H., Harms, H.K., Marquardt, T. Carbohydrate-deficient glycoprotein syndrome type Ib. Phosphomannose isomerase deficiency and mannose therapy. (1998) J. Clin. Invest. 101, 1414-20.
  5. ↑ Haeuptle, M.A., and Hennet, T. Congenital disorders of glycosylation: an update on defects affecting the biosynthesis of dolichol-linked oligosaccharides. (2009) Hum Mutat 30, 1628-41.
  6. ↑ Need AC, Shashi V, Hitomi Y et al. (June 2012). "Clinical application of exome sequencing in undiagnosed genetic conditions". J. Med. Genet. 49 (6): 353–61. doi:10.1136/jmedgenet-2012-100819. PMC 3375064. PMID 22581936.
  7. ↑ Enns GM, Shashi V, Bainbridge M et al. (March 2014). "Mutations in NGLY1 cause an inherited disorder of the endoplasmic reticulum-associated degradation pathway". Genet. Med. 16 (10): 751–8. doi:10.1038/gim.2014.22. PMID 24651605.
  8. ↑ Freeze HH, Eklund EA, Ng BG, Patterson MC (May 2012). "Neurology of inherited glycosylation disorders". Lancet Neurol. 11 (5): 453–66. doi:10.1016/S1474-4422(12)70040-6. PMID 22516080.
  9. ↑ Jaeken, J., Hennet, T., Matthijs, G., and Freeze, H.H. (2009) CDG nomenclature: time for a change! Biochim Biophys Acta. 1792, 825-6.
  10. ↑ Wu, X., Steet, R.A., Bohorov, O., Bakker, J., Newell, J., Krieger, M., Spaapen, L., Kornfeld, S., and Freeze, H.H. Mutation of the COG complex subunit gene COG7 causes a lethal congenital disorder. (2004) Nat. Med. 10, 518-23.
  11. ↑ Kornak U., Reynders E., Dimopoulou A., van Reeuwijk J., Fischer B., Rajab A., Budde B., Nürnberg P., -1#ARCL Debré-type Lefeber et al. (2008). "Impaired glycosylation and cutis laxa caused by mutations in the vesicular H+-ATPase subunit ATP6V0A2". Nat. Genet 40 (1): 32–4. doi:10.1038/ng.2007.45. PMID 18157129.
  12. ↑ Amberger J, Bocchini C, Hamosh A. (2011). "A new face and new challenges for Online Mendelian Inheritance in Man (OMIM®).". Hum Mutat. 32 (5): 564–7. doi:10.1002/humu.21466. PMID 21472891.
  13. ↑ Jensen H, Kjaergaard S, Klie F, Moller HU (2003). "Ophthalmic manifestations of congenital disorder of glycosylation type 1a". Ophthalmic Genet. 24 (2): 81–8. doi:10.1076/opge.24.2.81.13994. PMID 12789572.
  14. ↑ Sun L, Eklund EA, Chung WK, Wang C, Cohen J, Freeze HH (2005). "Congenital disorder of glycosylation id presenting with hyperinsulinemic hypoglycemia and islet cell hyperplasia". J. Clin. Endocrinol. Metab. 90 (7): 4371–5. doi:10.1210/jc.2005-0250. PMID 15840742.
  15. ↑ Züchner S, Dallman J, Wen R, Beecham G, Naj A, Farooq A, Kohli MA, Whitehead PL, Hulme W et al. (2011). "Whole-exome sequencing links a variant in DHDDS to retinitis pigmentosa". Am. J. Hum. Genet 88: 201–6. doi:10.1016/j.ajhg.2011.01.001.
  16. ↑ Cantagrel, V., Lefeber, D.J., Ng, B.G., Guan, Z., Silhavy, J.L., Bielas, S.L., Lehle, L., Hombauer, H., Adamowicz, M., Swiezewska, E., De Brouwer, A.P., Blümel, P., Sykut-Cegielska, .J, Houliston, S., Swistun, D., Ali, B.R., Dobyns, W.B., Babovic-Vuksanovic, D., van Bokhoven, H., Wevers, R.A., Raetz, C.R., Freeze, H.H., Morava, E., Al-Gazali, L., and Gleeson, J.G. SRD5A3 is required for converting polyprenol to dolichol and is mutated in a congenital glycosylation disorder. (2010) Cell, 142, 203-17
  17. ↑ Kranz C., Jungeblut C., Denecke J., Erlekotte A., Sohlbach C., Debus V., Kehl , Harms E., Reith A. et al. (2007). "A defect in dolichol phosphate biosynthesis causes a new inherited disorder with death in early infancy". Am. J. Hum. Genet 80: 433–40. doi:10.1086/512130. PMC 1821118. PMID 17273964.
  18. ↑ Wu X., Rush J.S., Karaoglu D., Krasnewich D., Lubinsky M.S., Waechter C.J., Gilmore R., Freeze H.H. (2003). "Deficiency of UDP-GlcNAc:Dolichol Phosphate N-Acetylglucosamine-1 Phosphate Transferase (DPAGT1) causes a novel congenital disorder of Glycosylation Type Ij.". Hum. Mut. 22 (2): 144–50. doi:10.1002/humu.10239. PMID 12872255.
  19. ↑ Grubenmann C.E., Frank C.G., Hülsmeier A.J., Schollen E., Matthijs G., Mayatepek E., Berger E.G., Aebi M., Hennet T. et al. (2004). "Deficiency of the first mannosylation step in the N-glycosylation pathway causes congenital disorder of glycosylation type Ik.". Hum. Mol. Genet 13 (5): 535–42. doi:10.1093/hmg/ddh050. PMID 14709599.
  20. ↑ Thiel C., Schwarz M., Peng J., Grzmil M., Hasilik M., Braulke T., Kohlschütter A., von Figura K., Lehle L. et al. (2003). "A new type of congenital disorders of glycosylation (CDG-Ii) provides new insights into the early steps of dolichol-linked oligosaccharide biosynthesis". J. Biol. Chem 278: 22498–505. doi:10.1074/jbc.m302850200.
  21. ↑ Rind N, Schmeiser V, Thiel C, Absmanner B, Lübbehusen J, Hocks J, Apeshiotis N, Wilichowski E, Lehle L et al. (2010). "A severe human metabolic disease caused by deficiency of the endoplasmatic mannosyltransferase hALG11 leads to congenital disorder of glycosylation-Ip". Hum. Mol. Genet 19 (8): 1413–24. doi:10.1093/hmg/ddq016. PMID 20080937.
  22. ↑ Vleugels W., Haeuptle M.A., Ng B.G., Michalski J.C., Battini R., Dionisi-Vici C., Ludman M.D., Jaeken J., Foulquier F. et al. (2009). "RFT1 deficiency in three novel CDG patients". Hum. Mutat 30: 1428–34. doi:10.1002/humu.21085.
  23. ↑ Körner C., Knauer R., Stephani U., Marquardt T., Lehle L., von Figura K. (1999). "Carbohydrate deficient glycoprotein syndrome type IV: deficiency of dolichyl-P-Man:Man(5)GlcNAc(2)-PP-dolichyl mannosyltransferase". EMBO J 18: 6816–22. doi:10.1093/emboj/18.23.6816.
  24. ↑ Frank C.G., Grubenmann C.E., Eyaid W., Berger E.G., Aebi M., Hennet T. (2004). "Identification and functional analysis of a defect in the human ALG9 gene: definition of congenital disorder of glycosylation type IL.". Am. J. Hum. Genet 75: 146–50. doi:10.1086/422367. PMC 1181998. PMID 15148656.
  25. ↑ Chantret I., Dupré T., Delenda C., Bucher S., Dancourt J., Barnier A., Charollais A., Heron D., Bader-Meunier B. et al. (2002). "Congenital disorders of glycosylation type Ig is defined by a deficiency in dolichyl-P-mannose:Man7GlcNAc2-PP-dolichyl mannosyltransferase". J. Biol. Chem 277: 25815–22. doi:10.1074/jbc.m203285200.
  26. ↑ Körner, C., Knauer, R., Holzbach, U., Hanefeld, F., Lehle, L., and von Figura, K. (1998) Carbohydrate-deficient glycoprotein syndrome type V: deficiency of dolichyl-P-Glc:Man9GlcNAc2-PP-dolichyl glucosyltransferase. Proc. Natl. Acad. Sci U S A., 95, 13200-5.
  27. ↑ Chantret I., Dancourt J., Dupré T., Delenda C., Bucher S., Vuillaumier-Barrot S., Ogier , de Baulny H., Peletan C. et al. (2003). "A deficiency in dolichyl-P-glucose:Glc1Man9GlcNAc2-PP-dolichyl alpha3-glucosyltransferase defines a new subtype of congenital disorders of glycosylation". J. Biol. Chem 278: 9962–71. doi:10.1074/jbc.m211950200.
  28. ↑ Kranz C., Denecke J., Lehrman M.A., Ray S., Kienz P., Kreissel G., Sagi D., Peter-Katalinic J., Freeze H.H. et al. (2001). "A mutation in the human MPDU1 gene causes congenital disorder of glycosylation type If (CDG-If)". J. Clin. Invest 108: 1613–9. doi:10.1172/jci200113635.
  29. ↑ Niehues R, Hasilik M, Alton G, Körner C, Schiebe-Sukumar M, Koch HG, Zimmer KP, Wu R, Harms E, Reiter K, von Figura K, Freeze HH, Harms HK, Marquardt T (1998). "Carbohydrate-deficient glycoprotein syndrome type Ib. Phosphomannose isomerase deficiency and mannose therapy". J. Clin. Invest. 101 (7): 1414–20. doi:10.1172/JCI2350. PMC 508719. PMID 9525984.
  30. ↑ Matthijs G, Schollen E, Pardon E, Veiga-Da-Cunha M, Jaeken J, Cassiman JJ, Van Schaftingen E (1997). "Mutations in PMM2, a phosphomannomutase gene on chromosome 16p13, in carbohydrate-deficient glycoprotein type I syndrome (Jaeken syndrome).". Nat. Genet. 16 (1): 88–92. doi:10.1038/ng0597-88. PMID 9140401.
  31. ↑ Lefeber DJ, Schönberger J, Morava E, Guillard M, Huyben KM, Verrijp K, Grafakou O, Evangeliou A, Preijers FW, Manta P, Yildiz J, Grünewald S, Spilioti M, van den Elzen C, Klein D, Hess D, Ashida H, Hofsteenge J, Maeda Y, van den Heuvel L, Lammens M, Lehle L, Wevers RA. (2009). "Deficiency of Dol-P-Man synthase subunit DPM3 bridges the congenital disorders of glycosylation with the dystroglycanopathies.". Am. J. Hum. Genet. 85 (1): 76–86. doi:10.1016/j.ajhg.2009.06.006. PMC 2706967. PMID 19576565.
  32. ↑ Mention, K., Lacaille, F., Valayannopoulos, V., Romano, S., Kuster, A., Cretz, M., Zaidan, H., Galmiche, L., Jaubert, F., de Keyzer, Y., Seta, N., and de Lonlay, P. Development of liver disease despite mannose treatment in two patients with CDG-Ib. (2008) Mol. Genet. Metab. 93, 40-3
  33. ↑ Westphal, V., Kjaergaard, S., Davis, J.A., Peterson, S.M., Skovby, F., and Freeze, H.H. Genetic and metabolic analysis of the first adult with congenital disorder of glycosylation type Ib: long-term outcome and effects of mannose supplementation. (2001) Mol. Genet. Metab. 73, 77-85.
  34. ↑ Eklund, E.A., and Freeze, H.H. The congenital disorders of glycosylation: a multifaceted group of syndromes. (2006) NeuroRx 3, 254-63.

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