Test Code: 1120

Congenital Disorders of Glycosylation: Deletion/Duplication Panel
Test Code: 1120
Turnaround time: 3 weeks

CONDITION DESCRIPTION

Congenital disorders of glycosylation (CDG) are a group of autosomal recessive genetic disorders caused by the alteration in synthesis and structure of protein and lipid glycosylation. In the past decade, over 30 genetic diseases have been identified that alter glycan synthesis, structure and ultimately the function of nearly all organ systems.

CDG type I (CDGI) disorders result from impaired synthesis of the incomplete lipid linked oligosaccharide (LLO) and/or its attachment to the growing polypeptide chain. CDG-Ia is the most common form reported, due to phosphomannomutase deficiency, an enzyme that converts mannose-6-phosphate to mannose-1-phosphate. CDG-Ib (phosphomannose isomerase, MPI deficiency) is the only known treatable form, by giving mannose orally. CDG type II (CDGII) includes defects in processing of N-glycans.

Phenotypes of this disorder are extremely variable. Manifestations range from severe developmental delay and hypotonia with multiple organ system involvement beginning in infancy, to hypoglycemia and protein-losing enteropathy with normal development. Most subtypes have been described in only a few individuals, however, thus understanding of the phenotypes is limited.

The current diagnostic test for CDG is analysis of serum transferrin glycoforms, also called “transferrin isoforms analysis”, or “carbohydrate-deficient transferrin analysis.” If positive, this testing can be followed by DNA testing to identify mutations in the gene involved. If a sample is not available for biochemical testing or if biochemical test results are inconclusive, this panel offers next generation sequence of CDG-associated genes.

References:
• Freeze HH. Congenital disorders of glycosylation: CDG-I, CDG-II, and beyond. Curr Mol Med 2007; 7:389-396.
• GeneTests: Congenital Disorders of Glycosylation Overview
• Jaeken J, Matthijs G. Congenital disorders of glycosylation: A rapidly expanding disease family. Annu Rev Genomics Hum Genet 2007;8:261- 278.

GENES

ALG11, ALG12, ALG13, ALG14, ALG2, ALG3, ALG6, ALG8, ALG9, ATP6V0A2, B3GALTL, B3GAT3, B4GALT1, B4GALT7, CHST14, CHST3, CHST6, CHSY1, COG1, COG4, COG5, COG6, COG7, COG8, DDOST, DHDDS, DOLK, DPAGT1, DPM1, DPM3, EXT1, EXT2, FKRP, FKTN, GALNT3, GFPT1, GNE, LARGE, LFNG, MAN1B1, MGAT2, MOGS, MPDU1, MPI, NGLY1, PGM1, PIGA, PIGL, PIGM, PIGO, PIGV, PMM2, POMGNT1, POMT1, POMT2, RFT1, SEC23B, SLC35A1, SLC35C1, SLC35D1, SRD5A3, ST3GAL3, ST3GAL5, TMEM165, TUSC3

INDICATIONS
This test is indicated for:

  • Confirmation of a clinical/biochemical diagnosis of a CDG, or when CDG is suspected and biochemical results are unavailable or inconclusive.
  • Carrier testing in adults with a family history of a CDG.

METHODOLOGY

Deletion/Duplication Analysis: DNA isolated from peripheral blood is hybridized to a gene-targeted CGH array to detect deletions and duplications. The targeted CGH array has overlapping probes that cover the entire genomic region.

Please note that a “backbone” of probes across the entire genome are included on the array for analytical and quality control purposes. Rarely, off- target copy number variants causative of disease may be identified that may or may not be related to the patient’s phenotype. Only known pathogenic off-target copy number variants will be reported. Off-target copy number variants of unknown clinical significance will not be reported.

DETECTION

Deletion/Duplication Analysis: Detection is limited to duplications and deletions. The CGH array will not detect point or intronic mutations. Results of molecular analysis must be interpreted in the context of the patient’s clinical and/or biochemical phenotype.

SPECIMEN REQUIREMENTS

Submit only 1 of the following specimen types
* Preferred specimen type: Whole Blood

Type: Whole Blood
Specimen Requirements:
In EDTA (purple top) or ACD (yellow top) tube: Infants (2 years): 3-5 ml
Older Children & Adults: 5-10 ml.

Specimen Collection and Shipping: Refrigerate until time of shipment. Ship sample within 5 days of collection at room temperature with overnight delivery.

Type: Isolated DNA
Specimen Requirements: In microtainer: 10 μg
Isolation using the QiagenTM Puregene kit for DNA extraction is recommended.

Specimen Collection and Shipping: Refrigerate until time of shipment in 100 ng/ul of TE buffer. Ship sample at room temperature with overnight delivery.

SPECIAL INSTRUCTIONS
Submit copies of diagnostic biochemical test results with the sample, if appropriate.
Sequence analysis is required before deletion/duplication analysis by targeted CGH array. If sequencing is performed by another third party provider, please submit a copy of the sequencing report with the test requisition.

RELATED TESTS
• Individual sequence analysis and deletion/duplication analysis is available for each of the genes in the panel.
• Congenital Disorders of Glycosylation: Sequencing Panel.
• Custom diagnostic mutation analysis (test code: 6875) is available to family members if mutations are identified by targeted mutation testing or sequencing analysis.