Genetic testing for vascular Ehlers-Danlos syndrome and other variants with fragility of the middle arteries
Article Category: Technical Report
Published Online: Sep 19, 2018
Page range: 42 - 44
DOI: https://doi.org/10.2478/ebtj-2018-0034
Keywords
© 2018 Yeltay Rakhmanov, Paolo Enrico Maltese, Alice Bruson, Marco Castori, Tommaso Beccari, Munis Dundar, Matteo Bertelli, published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.
(Other synonyms: classical Ehlers-Danlos syndrome with vascular fragility, vascular-like Ehlers-Danlos syndrome, kyphoscoliotic Ehlers-Danlos syndrome)
Ehlers-Danlos syndrome (EDS) is of a group of inherited connective tissue disorders caused by mutations in genes involved in extracellular matrix formation. The mutations cause a loss of structural integrity in different organ systems. Different types of EDS exist, distinguishable on the basis of the gene(s) involved, clinical manifestations and prognosis. The present module considers forms of EDS with vascular involvement. Among the various forms of EDS, vascular EDS (vEDS; OMIM 130050) is the most common among variants with a major risk of middle artery ruptures and fragility (e.g. spontaneous ruptures) of hollow organs. In most patients vEDS is defined by typical facial features (e.g. large eyes, small chin, sunken cheeks, thin nose and lips, lobeless ears), acrogeria, translucent skin with evident subcutaneous vessels on the trunk and lower back, easy bruising and severe arterial, digestive and uterine complications. Complications are vascular and include arterial and venous abnormalities with arterial rupture (1-3). vEDS is always caused by heterozygous mutations in the
Prevalence of EDS as a whole is estimated between 1/10,000 and 1/25,000, without significant ethnic variations. The “2017 International Classification of Ehlers-Danlos Syndromes and related disorders” identifies 13 clinical subtypes (4), among which vEDS probably accounts for about 5 to 10% of cases (5). The combination of two major criteria such as arterial rupture, intestinal rupture or uterine rupture during pregnancy and positive family history is strong diagnostic evidence of vEDS.
In cases who meet the clinical diagnostic criteria, genetic testing should be done to identify variations in
Differential diagnosis of vEDS should consider other forms of EDS, isolated arterial aneurysm, Loeys-Dietz syndromes, autosomal dominant polycystic kidney disease, Marfan syndrome, pseudoxanthoma elasticum and hereditary hemorrhagic telangiectasia (9).
vEDS regularly associates with mutations in
Pathogenic variants may include missense, nonsense, splicing, small insertions, small deletions, small indels, gross insertions, gross deletions and complex rearrangements.
To determine the gene defect responsible for the disease;
To confirm clinical diagnosis;
To assess the recurrence risk and perform genetic counselling for at-risk/affected individuals.
The test is listed in the Orphanet database and is offered by 23 accredited medical genetic laboratories in the EU, and in the GTR database, offered by 2 accredited medical genetic laboratories in the US.
Guidelines for clinical use of the test are described in Genetics Home Reference (
In clear-cut phenotypes, targeted Sanger sequencing of
Potentially causative variants and regions with low coverage are Sanger-sequenced. Sanger sequencing is also used for family segregation studies.
Multiplex Ligation Probe Amplification (MLPA) is used to detect duplications and deletions in the
To perform molecular diagnosis, a single sample of biological material is normally sufficient. This may be 1 ml peripheral blood in a sterile tube with 0.5 ml K3EDTA or 1 ml saliva in a sterile tube with 0.5 ml ethanol 95%. Sampling rarely has to be repeated.
Gene-disease associations and the interpretation of genetic variants are rapidly developing fields. It is therefore possible that the genes mentioned in this note may change as new scientific data is acquired. It is also possible that genetic variants today defined as of “unknown or uncertain significance” may acquire clinical importance.
Identification of pathogenic variants in the above genes confirms the clinical diagnosis and is an indication for family studies.
A pathogenic variant is known to be causative for a given genetic disorder based on previous reports, or predicted to be causative based on loss of protein function or expected significant damage to proteins or protein/protein interactions. In this way it is possible to obtain a molecular diagnosis in new/other subjects, establish the risk of recurrence in family members and plan preventive and/or therapeutic measures.
Detection of a variant of unknown or uncertain significance (
The absence of variations in the genomic regions investigated does not exclude a clinical diagnosis but suggests the possibility of:
alterations that cannot be identified by sequencing, such as large rearrangements that cause loss (deletion) or gain (duplication) of extended gene fragments;
sequence variations in gene regions not investigated by this test, such as regulatory regions (5’ and 3’ UTR) and deep intronic regions;
variations in other genes not investigated by the present test.
Unexpected results may emerge from the test, for example information regarding consanguinity, absence of family correlation or other genetically-based diseases.
If the identified pathogenic variant has autosomal dominant transmission, the probability that an affected carrier transmit the disease variant to his/her children is 50% in any pregnancy, irrespective of the sex of the child conceived.
In autosomal recessive mutations, both parents are usually healthy carriers. In this case, the probability of transmitting the disorder to the offspring is 25% in any pregnancy of the couple, irrespective of the sex of the child. An affected individual generates healthy carrier sons and daughters in all cases, except in pregnancies with a healthy carrier partner. In these cases, the risk of an affected son or daughter is 50%.
The test is limited by current scientific knowledge regarding the gene and disease.
NGS Analytical sensitivity >99.99%, with a minimum coverage of 10X; Analytical specificity 99.99%.
SANGER Analytical sensitivity >99.99%; Analytical specificity 99.99%.
MLPA Analytical sensitivity >99.99%; Analytical specificity 99.99%.
Clinical sensitivity: 95% for vEDS (10).
Clinical specificity: nearly 100% (10).
The genetic test is appropriate when:
the patient meets the diagnostic criteria for EDS with vascular involvement;
the sensitivity of the test is greater than or equal to that of tests described in the literature.
| Clinical management | Utility |
|---|---|
| Confirmation of clinical diagnosis | Yes |
| Differential diagnosis | Yes |
| Couple risk assessment | Yes |
| Availability of clinical trials can be checked on-line at | |