High mutation detection rates in cerebral cavernous malformation upon stringent inclusion criteria: one-third of probands are minors.

Cerebral cavernous malformations (CCM) are prevalent vascular malformations occurring in familial autosomal dominantly inherited or isolated forms. Once CCM are diagnosed by magnetic resonance imaging, the indication for genetic testing requires either a positive family history of cavernous lesions or clinical symptoms such as chronic headaches, epilepsy, neurological deficits, and hemorrhagic stroke or the occurrence of multiple lesions in an isolated case. Following these inclusion criteria, the mutation detection rates in a consecutive series of 105 probands were 87% for familial and 57% for isolated cases. Thirty-one novel mutations were identified with a slight shift towards proportionally more CCM3 mutations carriers than previously published (CCM1: 60%, CCM2: 18%, CCM3: 22%). In-frame deletions and exonic missense variants requiring functional analyses to establish their pathogenicity were rare: An in-frame deletion within the C-terminal FERM domain of CCM1 resulted in decreased protein expression and impaired binding to the transmembrane protein heart of glass (HEG1). Notably, 20% of index cases carrying a CCM mutation were below age 10 and 33% below age 18 when referred for genetic testing. Since fulminant disease courses during the first years of life were observed in CCM1 and CCM3 mutation carriers, predictive testing of minor siblings became an issue.

Predictive genetic testing of at-risk relatives requires analysis of all CCM genes after identification of an unclassified CCM1 variant in an individual affected with cerebral cavernous malformations.

The mutation detection rate for familial cerebral cavernous malformations (CCM) is extremely high, being about 90 % if direct sequencing of the three genes, CCM1, CCM2, and CCM3, is used in conjunction with quantitative analyses to detect larger CCM1-3 deletions/duplications. We here report on an individual who had presented with more than 30 cerebral and spinal cavernous malformations, two intracranial meningiomas, and disease manifestation only in the mid-forties. A CCM1 missense variant of unclear relevance was found during the first sequencing step. Thereafter, direct sequencing of all three CCM genes revealed the typical pathogenic loss-of-function mutation c.598C > T/p.Q200* in the CCM3 gene. Our results demonstrate that mutation analyses of all three CCM genes in the index patient regardless of previous identification of an unclassified CCM1 variant is crucial for reliable predictive testing of at-risk relatives.