Test Catalog

Test ID: CDGN    
Congenital Disorders of N-Glycosylation, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Screening for N-linked congenital disorders of glycosylation


Providing information on specific structural oligosaccharide abnormalities to potentially direct further genetic testing

Genetics Test Information Provides information that may help with selection of the correct genetic test or proper submission of the test request

Congenital disorders of glycosylation (CDG) comprise a large group of inborn errors of metabolism affecting predominantly N- and O-glycosylation of proteins.


N-linked CDG commonly present as clinical syndromes with multisystemic involvement and a broad clinical spectrum.


In addition to transferrin and apolipoprotein CIII isoform analysis, this test also detects and analyzes N-linked oligosaccharides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS) for a more comprehensive evaluation of CDG.

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

When this test is ordered, carbohydrate deficient transferrin for congenital disorders will always be performed at an additional charge.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Congenital disorders of glycosylation (CDG) are a group of over 100 inherited metabolic disorders affecting largely N- and O-glycosylation of proteins. Almost 50 inborn errors of metabolism are attributed to congenital defects in N-glycosylation, which takes place primarily in the cytoplasm and in the membranes of the endoplasmic reticulum. O-glycosylation defects are commonly tissue specific and present differently than classic N-linked defects. CDG are currently classified into 2 main groups. Type I CDG is characterized by defects in the assembly or transfer of the dolichol-linked glycan (sugar chain), while type II involves processing defects of the glycan. Depending on the specific defect, an N-glycosylation disorder can be either a type I or type II CDG.


N-linked CDG are phenotypically diverse, commonly presenting as clinical syndromes with multisystemic involvement and a broad clinical spectrum. There is considerable variation in the severity of this group of diseases ranging from a mild presentation in adults to severe multi-organ dysfunction causing infantile lethality. Intellectual disability is common, although in some subtypes, phosphomannose isomerase (MPI)-CDG (CDG-Ib) in particular, this is not observed. CDG should be considered in all patients with multisystem disease and in those with neurologic abnormalities including developmental delay and seizures, brain abnormalities such as cerebellar atrophy or hypoplasia as well as unexplained liver dysfunction. Additional common symptoms that may or may not be present include abnormal subcutaneous fat distribution, gastrointestinal issues such as vomiting, chronic diarrhea, and protein-losing enteropathy, eye abnormalities including retinal degeneration and strabismus, and cardiomyopathy.


Matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) analysis of released N-linked oligosaccharides, as is performed in this assay, is a global assessment of N-linked glycosylation. This complements the also performed transferrin and apolipoprotein CIII isoform analysis (see CDG / Carbohydrate Deficient Transferrin for Congenital Disorders of Glycosylation, Serum) by providing additional information on specific structural oligosaccharide abnormalities that can in turn guide molecular testing.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Interpretative comment only.

Interpretation Provides information to assist in interpretation of the test results

The results of the transferrin and apolipoprotein CIII isoform analysis are followed up with matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) analysis of released N-linked oligosaccharides to assess N-linked glycosylation. Reports of abnormal results will include recommendations for additional biochemical and molecular genetic studies to more precisely identify the specific congenital disorder of glycosylation (CDG). Treatment options, the name and telephone number of contacts who may provide studies, and a telephone number for one of the laboratory directors (if the referring physician has additional questions) will be provided.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

No significant cautionary statements

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Freeze HH: Congenital disorders of glycosylation: CDG-I, CDG II, and beyond. Curr Mol Med. 2007;7:389-396. doi: 10.2174/156652407780831548

2. Freeze HH, Eklund EA, Ng BG, Patterson MC: Neurology of inherited glycosylation disorders. Lancet Neurol. 2012;11:453- 466. doi: 10.1016/S1474-4422(12)70040-6

3. Hennet T, Cabalzar J: Congenital disorders of glycosylation: a concise chart of glycocalyx dysfunction. Trends Biochem Sci. 2015 Jul;40(7):377-384. doi: 10.1016/j.tibs.2015.03.002

4. Freeze HH, Chong JX, Bamshad MJ, Ng BG: Solving glycosylation disorders: fundamental approaches reveal complicated pathways. Am J Hum Genet. 2014 Feb 6;94(2):161-175. doi: 10.1016/j.ajhg.2013.10.024

5. Scott K, Gadomski T, Kozicz, Morava E: Congenital disorders of glycosylation: new defects and still counting. J Inherit Metab Dis. 2014;37:609-617. doi: 10.1007/s10545-014-9720-9

Special Instructions Library of PDFs including pertinent information and forms related to the test