Background Capillary malformation-arteriovenous malformation is an autosomal dominant disorder, characterised by capillary malformations and increased risk of fast-flow vascular malformations, caused by loss-of-function mutations in the RASA1 or EPHB4 genes. Around 25% of the patients do not seem to carry a germline mutation in either one of these two genes. Even if other genes could be involved, some individuals may have mutations in the known genes that escaped detection by less sensitive techniques. We tested the hypothesis that mosaic mutations could explain some of previously negative cases.
Methods DNA was extracted from peripheral blood lymphocytes, saliva or vascular malformation tissues from four patients. RASA1 and EPHB4 coding regions and exon/intron boundaries were analysed by targeted custom gene panel sequencing. A second panel and/or Sanger sequencing were used to confirm the identified mutations.
Results Four distinct mosaic RASA1 mutations, with an allele frequency ranging from 3% to 25%, were identified in four index patients with classical capillary malformation-arteriovenous malformation phenotype. Three mutations were known, one was novel. In one patient, a somatic second hit was also identified. One index case had three affected children, illustrating that the mosaicism was also present in the germline.
Conclusion This study shows that RASA1 mosaic mutations can cause capillary malformation-arteriovenous malformation. Thus, highly sensitive sequencing techniques should be considered as diagnostic tools, especially for patients with no family history. Even low-level mosaicism can cause the classical phenotype and increased risk for offspring. In addition, our study further supports the second-hit pathophysiological mechanism to explain the multifocality of vascular lesions in this disorder.
- capillary malformation-arteriovenous malformation
- mosaic mutation
- second hit
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Contributors NR and MV designed and directed the project. EF, MR and PB performed the interpretation of the molecular data. PB directed the cDNA analysis. RH provided bioinformatics support for the use of Highlander. NR, ABB, CWTC, MG, VD, ADI, LMB and MV provided clinical expertise, patient recruitment and collection of samples. NR wrote the manuscript and all authors commented on the manuscript.
Funding This study was financially supported by the Fonds de la Recherche Scientifique (FNRS Grant T.0026.14 to MV and Grant T.0146.16 to LMB), and the Generet Prize, Fondation Roi Baudouin, Belgium (to MV).
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval Ethics Committee of the Medical Faculty of Université Catholique de Louvain (2016/10OCT/438) updated on 15 January 2018.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement All data relevant to the study are included in the article or uploaded as supplementary information.