<abstract xmlns="http://www.w3.org/1999/xhtml"><p>We studied the scientific literature and disease guidelines to summarize the clinical utility of genetic testing for lymphedema distichiasis (LD) syndrome. LD is inherited in an autosomal dominant manner, and has unknown prevalence. It is caused by variations in the <italic>FOXC2</italic> gene. Clinical diagnosis involves clinical examination, targeted at identifying primary lymphedema (chronic swelling of the extremities) and distichiasis (double row of eyelashes). The genetic test is useful for confirming diagnosis, as well as for differential diagnosis, couple risk assessment and access to clinical trials.</p></abstract>

We studied the scientific literature and disease guidelines to summarize the clinical utility of genetic testing for lymphedema distichiasis (LD) syndrome. LD is inherited in an autosomal dominant manner, and has unknown prevalence. It is caused by variations in the FOXC2 gene. Clinical diagnosis involves clinical examination, targeted at identifying primary lymphedema (chronic swelling of the extremities) and distichiasis (double row of eyelashes). The genetic test is useful for confirming diagnosis, as well as for differential diagnosis, couple risk assessment and access to clinical trials.

<div xmlns="http://www.w3.org/1999/xhtml"><sec id="j_ebtj-2018-0026_s_001_w2aab3b7b3b1b6b1ab1aAa"><div>Lymphedema-distichiasis syndrome</div><p>(Other synonyms: Distichiasis-lymphedema syndrome; lymphedema with distichiasis)</p></sec><sec id="j_ebtj-2018-0026_s_002_w2aab3b7b3b1b6b1ab1b1Aa"><div>General information about the disease</div><p>Lymphedema-distichiasis (LD, OMIM disease 153400) syndrome is a rare genetic disorder that affects the lymphatic system. It combines lymphedema of the lower extremities and double rows of eyelashes (aberrant eyelashes ranging from a full set of extra eyelashes to a single hair) (<a ref-type="bibr" href="#j_ebtj-2018-0026_ref_001_w2aab3b7b3b1b6b1ab1c11b1Aa">1</a>). Affected individuals may also have renal abnormalities (nephritis, duplex kidney, recurrent infections, chronic sclerosing glomerulopathy), diabetes mellitus (<a ref-type="bibr" href="#j_ebtj-2018-0026_ref_002_w2aab3b7b3b1b6b1ab1c11b2Aa">2</a>), varicose veins, cleft palate, extradural cysts, congenital heart defects (tetralogy of Fallot, ventricular septal defects), ocular findings, such as photophobia, exotropia, droopy eyelids (ptosis), ectropion and cataracts (<a ref-type="bibr" href="#j_ebtj-2018-0026_ref_003_w2aab3b7b3b1b6b1ab1c11b3Aa">3</a>, <a ref-type="bibr" href="#j_ebtj-2018-0026_ref_004_w2aab3b7b3b1b6b1ab1c11b4Aa">4</a>).</p><p>The estimated prevalence of LD is currently unknown.</p><p>The clinical diagnosis of LD is based on: primary lymphedema (chronic swelling of the extremities caused by intrinsic dysfunction of the lymphatic vessels); distichiasis (aberrant and/or extra row of eyelashes originating from the tarsal gland) (<a ref-type="bibr" href="#j_ebtj-2018-0026_ref_001_w2aab3b7b3b1b6b1ab1c11b1Aa">1</a>).</p><p>Approximately 80% of individuals with lymphedema-distichiasis syndrome have lymphedema by early adulthood (age 30 years), although a few individuals may develop lymphedema later. Approximately 94% of affected individuals also have distichiasis (<a ref-type="bibr" href="#j_ebtj-2018-0026_ref_005_w2aab3b7b3b1b6b1ab1c11b5Aa">5</a>).</p><p>Differential diagnosis is necessary with respect to other diseases that manifest lymphedema or distichiasis, including Milroy disease, Meige disease microcephaly with/without chorioretinopathy, lymphedema, or mental retardation, Emberger syndrome, hypotrichosis lymphedema telangiectasia syndrome, yellow nail syndrome, blepharocheilodontic syndrome, isolated distichiasis, and trichiasis (<a ref-type="bibr" href="#j_ebtj-2018-0026_ref_001_w2aab3b7b3b1b6b1ab1c11b1Aa">1</a>).</p><p>LD is inherited in an autosomal dominant manner, although approximately one quarter of cases are the result of <italic>de novo</italic> mutations. Fang et al. identified mutations in the <italic>FOXC2</italic> (Forkhead Box C2, OMIM gene 602402) gene as a cause of LD Syndrome. The single exon 1.5 kb <italic>FOXC2</italic> gene is a member of the ‘forkhead’ (or winged helix) gene family, originally identified in Drosophila, which encodes transcription factors with a conserved 100-amino acid DNA binding motif. About 60 different causative <italic>FOXC2</italic> mutations have been reported (<a ref-type="bibr" href="#j_ebtj-2018-0026_ref_002_w2aab3b7b3b1b6b1ab1c11b2Aa">2</a>). The specific function of <italic>FOXC2</italic> has not yet been determined; however, it may play a role in mesenchymal and adipose tissues, and heart development (<a ref-type="bibr" href="#j_ebtj-2018-0026_ref_006_w2aab3b7b3b1b6b1ab1c11b6Aa">6</a>), and has been found to play a role in the Hedgehog (Hh) signaling pathway (<a ref-type="bibr" href="#j_ebtj-2018-0026_ref_007_w2aab3b7b3b1b6b1ab1c11b7Aa">7</a>).</p><p>Pathogenic variants in FOXC2 are identified in 95% of cases with LD (<a ref-type="bibr" href="#j_ebtj-2018-0026_ref_001_w2aab3b7b3b1b6b1ab1c11b1Aa">1</a>). Since 5% of patients with LD does not carry pathogenic variants in FOXC2, genetic heterogeneity can be hypothesized.</p><p>Pathogenic variants are either gain-of-function or loss-of-function and may include missense, nonsense, small insertions and deletions, small indels and gross deletions or duplications.</p></sec><sec id="j_ebtj-2018-0026_s_003_w2aab3b7b3b1b6b1ab1b2Aa"><div>Aims of the test</div><list list-type="bullet"><list-item><p>To determine the gene defect responsible for the disease;</p></list-item><list-item><p>To confirm clinical diagnosis;</p></list-item><list-item><p>To assess the recurrence risk and perform genetic counselling for at-risk/affected individuals.</p></list-item></list></sec><sec id="j_ebtj-2018-0026_s_004_w2aab3b7b3b1b6b1ab1b3Aa"><div>Test characteristics</div><sec id="j_ebtj-2018-0026_s_004_s_001_w2aab3b7b3b1b6b1ab1b3b1Aa"><div>Specialist centers/ Published Guidelines</div><p>The test is listed in the Orphanet database and is offered by 47 accredited medical genetic laboratories in the EU, and in the GTR database, offered by 14 accredited medical genetic laboratories in the US.</p><p>Guidelines for clinical use of the test are described in Genetics Home Reference (<ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://ghr.nlm.nih.gov">ghr.nlm.nih.gov</ext-link>) and Gene Reviews (<a ref-type="bibr" href="#j_ebtj-2018-0026_ref_001_w2aab3b7b3b1b6b1ab1c11b1Aa">1</a>).</p></sec><sec id="j_ebtj-2018-0026_s_004_s_002_w2aab3b7b3b1b6b1ab1b3b2Aa"><div>Test strategy</div><p>Since it is single gene disorder, we advise Sanger sequencing for the detection of nucleotide variations in coding exons and flanking introns in the <italic>FOXC2</italic> gene. Sanger sequencing is also used for family segregation studies.</p><p>Multiplex Ligation Probe Amplification (MLPA) is used to detect duplications and deletions in <italic>FOXC2</italic>.</p><p>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 K<sub>3</sub>EDTA 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.</p></sec></sec><sec id="j_ebtj-2018-0026_s_005_w2aab3b7b3b1b6b1ab1b4Aa"><div>Genetic test results</div><sec id="j_ebtj-2018-0026_s_005_s_001_w2aab3b7b3b1b6b1ab1b4b1Aa"><div>Positive</div><p>Identification of pathogenic variants in the <italic>FOXC2</italic> confirms the clinical diagnosis and is an indication for family studies.</p><p>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.</p></sec><sec id="j_ebtj-2018-0026_s_005_s_002_w2aab3b7b3b1b6b1ab1b4b2Aa"><div>Inconclusive</div><p>Detection of a variant of unknown or uncertain significance (<italic>VUS</italic>): a new variation without any evident pathogenic significance or a known variation with insufficient evidence (or with conflicting evidence) to indicate it is <italic>likely benign</italic> or <italic>likely pathogenic</italic> for a given genetic disorder. In these cases, it is advisable to extend testing to the patient’s relatives to assess variant segregation and clarify its contribution. In some cases, it could be necessary to perform further examinations/tests or to do a clinical reassessment of pathological signs.</p></sec><sec id="j_ebtj-2018-0026_s_005_s_003_w2aab3b7b3b1b6b1ab1b4b3Aa"><div>Negative</div><p>The absence of variations in the genomic regions investigated does not exclude a clinical diagnosis but suggests the possibility of:</p><list list-type="bullet"><list-item><p>alterations that cannot be identified by sequencing, such as large rearrangements that cause loss (deletion) or gain (duplication) of extended gene fragments;</p></list-item><list-item><p>sequence variations in gene regions not investigated by this test, such as regulatory regions (5’ and 3’ UTR) and deep intronic regions;</p></list-item><list-item><p>variations in other genes not investigated by the present test.</p></list-item></list></sec><sec id="j_ebtj-2018-0026_s_005_s_004_w2aab3b7b3b1b6b1ab1b4b4Aa"><div>Unexpected</div><p>Unexpected results may emerge from the test, for example information regarding consanguinity, absence of family correlation or other genetically based diseases.</p></sec></sec><sec id="j_ebtj-2018-0026_s_006_w2aab3b7b3b1b6b1ab1b5Aa"><div>Risk for progeny</div><p>In autosomal dominant transmission, the probability that an affected carrier transmit the variant to his/her children is 50% in any pregnancy, irrespective of the sex of the child conceived.</p></sec><sec id="j_ebtj-2018-0026_s_007_w2aab3b7b3b1b6b1ab1b6Aa"><div>Limits of the test</div><p>The test is limited by current scientific knowledge regarding the gene and disease.</p></sec><sec id="j_ebtj-2018-0026_s_008_w2aab3b7b3b1b6b1ab1b7Aa"><div>Analytical sensitivity (proportion of positive tests when the genotype is truly present) and specificity (proportion of negative tests when the genotype is not present)</div><p>SANGER Analytical sensitivity >99.99%; Analytical specificity 99.99%.</p><p>MLPA Analytical sensitivity >99.99%; Analytical specificity 99.99%.</p></sec><sec id="j_ebtj-2018-0026_s_009_w2aab3b7b3b1b6b1ab1b8Aa"><div>Clinical sensitivity (proportion of positive tests if the disease is present) and clinical specificity (proportion of negative tests if the disease is not present)</div><p>Clinical sensitivity: Variations in <italic>FOXC2</italic> gene are identified in 95% of LD (<a ref-type="bibr" href="#j_ebtj-2018-0026_ref_001_w2aab3b7b3b1b6b1ab1c11b1Aa">1</a>).</p><p>Clinical specificity is estimated at approximately 99.99% (Author’s laboratory data) (<a ref-type="bibr" href="#j_ebtj-2018-0026_ref_008_w2aab3b7b3b1b6b1ab1c11b8Aa">8</a>).</p></sec><sec id="j_ebtj-2018-0026_s_010_w2aab3b7b3b1b6b1ab1b9Aa"><div>Prescription appropriateness</div><p>The genetic test is appropriate when:</p><list list-type="order"><list-item><label>a)</label><p>the patient meets the diagnostic criteria for LD;</p></list-item><list-item><label>b)</label><p>the sensitivity of the test is greater than or equal to that of tests described in the literature.</p></list-item></list></sec><sec id="j_ebtj-2018-0026_s_011_w2aab3b7b3b1b6b1ab1c10Aa"><div>Clinical utility</div><table-wrap id="j_ebtj-2018-0026_tab_001_w2aab3b7b3b1b6b1ab1c10b1Aa" position="float" orientation="portrait"><table rules="all"><thead><tr><th align="left">Clinical management</th><th align="center">Utility</th></tr></thead><tbody><tr><td align="left">Confirmation of clinical diagnosis</td><td align="center">Yes</td></tr><tr><td align="left">Differential diagnosis</td><td align="center">Yes</td></tr><tr><td align="left">Couple risk assessment</td><td align="center">Yes</td></tr><tr><td align="left" colspan="2">Availability of clinical trials can be checked on-line at <ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://htps://clinicaltrials.gov/">htps://clinicaltrials.gov/</ext-link></td></tr></tbody></table></table-wrap></sec></div>

Genetic testing for lymphedema-distichiasis syndrome

The EuroBiotech Journal

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

{"article-title":"Genetic testing for lymphedema-distichiasis syndrome"}

We studied the scientific literature and disease guidelines to summarize the clinical utility of genetic testing for lymphedema distichiasis (LD) syndrome. LD...

Genetic testing for lymphedema-distichiasis syndrome

Article Category: Technical Report

Publié en ligne: 19 sept. 2018

Pages: 13 - 15

DOI: https://doi.org/10.2478/ebtj-2018-0026

Mots clés
Lymphedema-distichiasis syndrome, EBTNA UTILITY GENE TEST

© 2018 Yeltay Rakhmanov, Paolo Enrico Maltese, Stefano Paolacci, Carla Marinelli, Matteo Bertelli, published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Genetic testing for lymphedema-distichiasis syndrome

Article Category: Technical Report

Publié en ligne: 19 sept. 2018

Pages: 13 - 15

DOI: https://doi.org/10.2478/ebtj-2018-0026

Mots clésLymphedema-distichiasis syndrome, EBTNA UTILITY GENE TEST

© 2018 Yeltay Rakhmanov, Paolo Enrico Maltese, Stefano Paolacci, Carla Marinelli, Matteo Bertelli, published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Mots clés
Lymphedema-distichiasis syndrome, EBTNA UTILITY GENE TEST