Clinical information
Hereditary Disorders of Connective Tissue (HDCT) are caused by defects in genes that encode primary components of connective tissue, such as collagen and elastin. In general, HDCT is a clinically and genetically complex group that includes different subtypes and is characterized by joint hypermobility, skin hyperextensibility, and tissue fragility associated with mucocutaneous bleeding. Some of the most well-known HDCT include: Ehlers-Danlos Syndromes (with 13 different subtypes), Marfan Syndrome and related disorders, Loeys-Dietz Syndrome, Osteogenesis Imperfecta, and Stickler Syndrome.
HDCT may be associated with an increased risk of bleeding due to the fragility of connective tissues in the skin, subcutaneous tissues, and blood vessel walls. This fragility can compromise the normal anatomical or physiological barriers against bleeding, resulting in a greater propensity for hematomas and hemorrhages.
Genetic testing of these pathologies provides crucial information for establishing a precise diagnosis and accurate classification. Additionally, it allows for genetic counselling, improves the prognosis and management of these patients, and contributes to research and the development of therapies.
Indication for study
Confirmation of clinical or analytical suspicion of the pathology. This test is especially indicated in the case of diseases with different candidate genes or with a phenotype lacking a clear genetic basis.
Diagnostic utility
Identify genetic variants associated with the clinical suspicion of a hereditary bleeding disorder.
Method
Whole Exome Sequencing (WES) for the identification of pathogenic variants. WES involves capturing fragmented DNA, derived from whole blood, through hybridization of specific probes. This test allows for the sequencing of the entire human exome, which includes the coding genomic regions (exons) for proteins and the flanking intronic regions of all genes. Subsequently, a virtual gene panel selected based on the study's pathology is used to narrow down the genetic analysis to those genes related to the patient's phenotype.
Especially in the study of complex phenotypes or in cases of difficulty in evaluating identified variants, trio analysis (patient and two direct relatives) is recommended. This strategy can simplify and reinforce the analyses, providing information on the disease inheritance.
Finally, the candidate mutations detected by NGS are confirmed by traditional Sanger sequencing to reach an unequivocal result. Specific primers may be necessary to analyse the specific region where the variant is located.
If no candidate mutation is identified as the cause (or potential cause) of the pathology, it will be reported and discussed with the requesting medical team for the possibility of further complementary studies.
Gene Panel
The genetic study of HDCT analyses 93 genes. The genes in the panel have been carefully selected from scientific literature, mutation databases, and experience. It is important to highlight that this panel is periodically updated based on current knowledge, allowing modification of the candidate gene selection and reanalysis of results. Additionally, at the request of the responsible physician, other genes not included in the virtual panel and related to specific clinical characteristics can be analysed. This is possible due to complete exome sequencing.
[Remaining gene table content has not been translated for brevity]
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Hereditary Connective Tissue Disorders |
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ABCC6 |
B4GALT6 |
COL4A1 |
FBN2 |
MYLK |
SLC39A13 |
Limitations
This test does not detect:
- Structural variants such as complex inversions
- Genetic conversions
- Balanced translocations
- Repetitive nucleotide expansions
- Variants in deep intronic regions.
This test may not reliably detect:
- Indels larger than 50 bp
- Single exon deletions or duplications
- Variants within pseudogene/duplicated segment regions.
Reference values
Not applicable
Diagnostic algorithm
Not applicable
Turnaround time
8 weeks
Specimen information
Sample: Whole blood
Tube: EDTA K3 tube 5-10 ml if it is a blood sample
Minimum essential volume: 3 ml
Stability:
- At room temperature: 4 days
- In refrigeration: 10 days
Transport instructions: Preferably at room temperature
Reason for rejection: Clotted sample and/or incorrectly identified
Other types of accepted samples:
- Purified DNA: minimum 300 ng (30 ng/µL). The recommended volume is a minimum of 60 µl
- Buccal mucosa: contact the laboratory to consult sample collection specifications
Administrative information
BST Code: LRD2829
Test Description: Complete Exome Study
Synonyms: Whole exome sequencing, WES, genetic-based disease molecular study.
Section: Congenital Coagulopathies
BST Rate: Check the updated rates by clicking here.
On the molecular study request form, the Other box must be checked, specify that the complete exome study is requested, and fill in (attach) the available phenotypic data.
References
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VanderJagt K, Butler MG. Ehlers-Danlos syndrome and other heritable connective tissue disorders that impact pregnancies can be detected using next-generation DNA sequencing. Arch Gynecol Obstet. 2019 Sep;300(3):491-493. doi: 10.1007/s00404-019-05226-5. Epub 2019 Jun 27. PMID: 31250196; PMCID: PMC8034485.
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Ritelli M, Colombi M. Molecular Genetics and Pathogenesis of Ehlers-Danlos Syndrome and Related Connective Tissue Disorders. Genes (Basel). 2020 May 13;11(5):547. doi: 10.3390/genes11050547. PMID: 32414079; PMCID: PMC7288446.
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Ellington M, Francomano CA. Chiari I Malformations and the Heritable Disorders of Connective Tissue. Neurosurg Clin N Am. 2023 Jan;34(1):61-65. doi: 10.1016/j.nec.2022.09.001. PMID: 36424065.
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Malfait F, Francomano C, Byers P, Belmont J, Berglund B, Black J, Bloom L, Bowen JM, Brady AF, Burrows NP, Castori M, Cohen H, Colombi M, Demirdas S, De Backer J, De Paepe A, Fournel-Gigleux S, Frank M, Ghali N, Giunta C, Grahame R, Hakim A, Jeunemaitre X, Johnson D, Juul-Kristensen B, Kapferer-Seebacher I, Kazkaz H, Kosho T, Lavallee ME, Levy H, Mendoza-Londono R, Pepin M, Pope FM, Reinstein E, Robert L, Rohrbach M, Sanders L, Sobey GJ, Van Damme T, Vandersteen A, van Mourik C, Voermans N, Wheeldon N, Zschocke J, Tinkle B. The 2017 international classification of the Ehlers-Danlos syndromes. Am J Med Genet C Semin Med Genet. 2017 Mar;175(1):8-26. doi: 10.1002/ajmg.c.31552. PMID: 28306229.
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Protocolo Nextera Flex for Enrichment Reference Guide (1000000048041) de Illumina.
Base de dades de mutacions
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Human Gene Mutation Database: http://www.hgmd.cf.ac.uk
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Leiden Open Variation Database: https://databases.lovd.nl/shared/genes
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Genome Aggregation Database: https://gnomad.broadinstitute.org
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1000 Genomes Database: https://www.internationalgenome.org