Novel CCM2 missense variants abrogating the CCM1-CCM2 interaction cause cerebral cavernous malformations.

BACKGROUND: Cerebral cavernous malformations (CCMs) are vascular malformations mostly located within the central nervous system. Most deleterious variants are loss of function mutations in one of the three CCM genes. These genes code for proteins that form a ternary cytosolic complex with CCM2 as a hub. Very few CCM2 missense variants have been shown to be deleterious by modifying the ternary CCM complex stability. OBJECTIVES: To investigate the causality of novel missense CCM2 variants detected in patients with CCM. METHODS: The three CCM genes were screened in 984 patients referred for CCM molecular screening. Interaction between CCM1 and CCM2 proteins was tested using co-immunoprecipitation experiments for the CCM2 missense variants located in the phosphotyrosine binding (PTB) domain. RESULTS: 11 distinct CCM2 rare missense variants were found. Six variants predicted to be damaging were located in the PTB domain, four of them were novel. When co-transfected with CCM1 in HEK293T cells, a loss of interaction between CCM1 and CCM2 was observed for all six variants. CONCLUSION: We showed, using co-immunoprecipitation experiments, that CCM2 missense variants located in the PTB domain were actually damaging by preventing the normal interaction between CCM1 and CCM2. These data are important for diagnosis and genetic counselling, which are challenging in patients harbouring such variants.

Clinical and Molecular Features of 5 European Multigenerational Families With Moyamoya Angiopathy.

Background and Purpose Moyamoya angiopathy (MMA) is a rare cerebral vasculopathy outside of Asia. In Japanese patients, a vast majority of patients carry the founder p.R4810K variant in the RNF213 gene, and familial cases are around 10%. In European patients, data about familial occurrence are limited. The aim of this study was to characterize the clinical and molecular features of several European families with a parent-to-child transmission of MMA. Methods Out of 126 MMA probands referred, we identified 113 sporadic probands and 13 familial probands. Segregation analysis showed a vertical parent-to-child pattern of inheritance in the families of 5 of these probands. All 5 families were of German or Dutch ancestry. We investigated the clinical features of affected members and used whole-exome sequencing to screen RNF213 and 13 genes involved in Mendelian MMA and to identify genes recurrently mutated in these families. Results Twelve affected MMA patients were identified, including 9 females and 3 males. Age at clinical onset ranged from 11 to 65 years. In 3 of 5 families, associated livedo racemosa was found. We did not detect any deleterious variants in the 13 known MMA genes. RNF213 rare missense variants predicted to be pathogenic were detected in all affected members of 2 of these families, as well as 2 candidate variants of the PALD1 gene. Conclusions Nonsyndromic MMA was identified in 5 European families, including 2 to 3 clinically affected cases segregating with a parent-to-child pattern of inheritance in each family. Molecular screening detected rare deleterious variants within RNF213 and PALD1 in all affected members of 2 of these 5 families, as well as in some clinically unaffected members. Altogether these data raise the difficult and, to date unanswered, question of the medical indication of presymptomatic screening.

Rare RNF213 variants in the C-terminal region encompassing the RING-finger domain are associated with moyamoya angiopathy in Caucasians.

Moyamoya angiopathy (MMA) is a cerebral angiopathy affecting the terminal part of internal carotid arteries. Its prevalence is 10 times higher in Japan and Korea than in Europe. In East Asian countries, moyamoya is strongly associated to the R4810K variant in the RNF213 gene that encodes for a protein containing a RING-finger and two AAA+ domains. This variant has never been detected in Caucasian MMA patients, but several rare RNF213 variants have been reported in Caucasian cases. Using a collapsing test based on exome data from 68 European MMA probands and 573 ethnically matched controls, we showed a significant association between rare missense RNF213 variants and MMA in European patients (odds ratio (OR)=2.24, 95% confidence interval (CI)=(1.19-4.11), P=0.01). Variants specific to cases had higher pathogenicity predictive scores (median of 24.2 in cases versus 9.4 in controls, P=0.029) and preferentially clustered in a C-terminal hotspot encompassing the RING-finger domain of RNF213 (P<10-3). This association was even stronger when restricting the analysis to childhood-onset and familial cases (OR=4.54, 95% CI=(1.80-11.34), P=1.1 × 10-3). All clinically affected relatives who were genotyped were carriers. However, the need for additional factors to develop MMA is strongly suggested by the fact that only 25% of mutation carrier relatives were clinically affected.

De novo mutations in CBL causing early-onset paediatric moyamoya angiopathy.

BACKGROUND: Moyamoya angiopathy (MMA) is characterised by a progressive stenosis of the terminal part of the internal carotid arteries and the development of abnormal collateral deep vessels. Its pathophysiology is unknown. MMA can be the sole manifestation of the disease (moyamoya disease) or be associated with various conditions (moyamoya syndrome) including some Mendelian diseases. We aimed to investigate the genetic basis of moyamoya using a whole exome sequencing (WES) approach conducted in sporadic cases without any overt symptom suggestive of a known Mendelian moyamoya syndrome. METHODS: A WES was performed in four unrelated early-onset moyamoya sporadic cases and their parents (trios). Exome data were analysed under dominant de novo, autosomal recessive and X-linked hypotheses. A panel of 17 additional sporadic cases with early-onset moyamoya was available for mutation recurrence analysis. RESULTS: We identified two germline de novo mutations in CBL in two out of the four trio probands, two girls presenting with an infancy-onset severe MMA. Both mutations were predicted to alter the ubiquitin ligase activity of the CBL protein that acts as a negative regulator of the RAS pathway. These two germline CBL mutations have previously been described in association with a developmental Noonan-like syndrome and susceptibility to juvenile myelomonocytic leukaemia (JMML). Notably, the two mutated girls never developed JMML and presented only subtle signs of RASopathy that did not lead to evoke this diagnosis during follow-up. CONCLUSIONS: These data suggest that CBL gene screening should be considered in early-onset moyamoya, even in the absence of obvious signs of RASopathy.

Cerebral cavernous malformations arise independent of the heart of glass receptor.

BACKGROUND AND PURPOSE: The Heart of Glass (HEG) receptor binds KRIT1 and functions with KRIT1, CCM2, and PDCD10 in a common signaling pathway required for heart and vascular development. Mutations in KRIT1, CCM2, and PDCD10 also underlie human cerebral cavernous malformation (CCM) and postnatal loss of these genes in the mouse endothelium results in rapid CCM formation. Here, we test the role of HEG in CCM formation in mice and in humans. METHODS: We constitutively or conditionally deleted Heg and Ccm2 genes in genetically modified mice. Mouse embryos, brain, and retina tissues were analyzed to assess CCM lesion formation. RESULTS: In postnatal mice, CCMs form with Ccm2-/- but not with Heg-/- or Heg-/-;Ccm2+/- endothelial cells. Consistent with these findings, human patients with CCM who lack exonic mutations in KRIT1, CCM2, or PDCD10 do not have mutations in HEG. CONCLUSIONS: These findings suggest that the HEG-CCM signaling functions during cardiovascular development and growth, whereas CCMs arise because of loss of HEG-independent CCM signaling in the endothelium of the central nervous system after birth.

Loss of BRCC3 deubiquitinating enzyme leads to abnormal angiogenesis and is associated with syndromic moyamoya.

Moyamoya is a cerebrovascular angiopathy characterized by a progressive stenosis of the terminal part of the intracranial carotid arteries and the compensatory development of abnormal and fragile collateral vessels, also called moyamoya vessels, leading to ischemic and hemorrhagic stroke. Moyamoya angiopathy can either be the sole manifestation of the disease (moyamoya disease) or be associated with various conditions, including neurofibromatosis, Down syndrome, TAAD (autosomal-dominant thoracic aortic aneurysm), and radiotherapy of head tumors (moyamoya syndromes). Its prevalence is ten times higher in Japan than in Europe, and an estimated 6%-12% of moyamoya disease is familial in Japan. The pathophysiological mechanisms of this condition remain obscure. Here, we report on three unrelated families affected with an X-linked moyamoya syndrome characterized by the association of a moyamoya angiopathy, short stature, and a stereotyped facial dysmorphism. Other symptoms include an hypergonadotropic hypogonadism, hypertension, dilated cardiomyopathy, premature coronary heart disease, premature hair graying, and early bilateral acquired cataract. We show that this syndromic moyamoya is caused by Xq28 deletions removing MTCP1/MTCP1NB and BRCC3. We also show that brcc3 morphant zebrafish display angiogenesis defects that are rescued by endothelium-specific expression of brcc3. Altogether, these data strongly suggest that BRCC3, a deubiquitinating enzyme that is part of the cellular BRCA1 and BRISC complexes, is an important player in angiogenesis and that BRCC3 loss-of-function mutations are associated with moyamoya angiopathy.

Recent insights into cerebral cavernous malformations: the molecular genetics of CCM.

Cerebral cavernous malformations (CCM) are vascular lesions which can occur as a sporadic (80% of the cases) or familial autosomal dominant form (20%). Three CCM genes have been identified: CCM1/KRIT1, CCM2/MGC4607 and CCM3/PDCD10. Almost 80% of CCM patients affected with a genetic form of the disease harbor a heterozygous germline mutation in one of these three genes. Recent work has shown that a two-hit mechanism is involved in CCM pathogenesis which is caused by a complete loss of any of the three CCM proteins within endothelial cells lining the cavernous capillary cavities. These data were an important step towards the elucidation of the mechanisms of this condition.

Genetics of cavernous angiomas.

Cerebral cavernous malformations (CCM) are vascular malformations that can occur as a sporadic or a familial autosomal dominant disorder. Clinical and cerebral MRI data on large series of patients with a genetic form of the disease are now available. In addition, three CCM genes have been identified: CCM1/KRIT1, CCM2/MGC4607, and CCM3/PDCD10. These recent developments in clinical and molecular genetics have given us useful information about clinical care and genetic counselling and have broadened our understanding of the mechanisms of this disorder.

Genotype-phenotype correlations in cerebral cavernous malformations patients.

OBJECTIVE: To compare clinical features of CCM1, CCM2, and CCM3 mutation carriers. METHODS: A detailed clinical and molecular analysis of 163 consecutive cerebral cavernous malformation (CCM) families was performed. RESULTS: A deleterious mutation was detected in 128 probands. Three hundred thirty-three mutation carriers were identified (238 CCM1, 67 CCM2, and 28 CCM3). Ninety-four percent of the probands with an affected relative had a mutation compared with 57% of the probands with multiple lesions but no affected relative (p < 0.001). The number of affected individuals per family was lower in CCM3 families (p < 0.05). The proportion of patients with onset of symptoms before 15 years of age was higher in the CCM3 group (p < 0.0025). Cerebral hemorrhage was the most common initial presentation in CCM3 patients. The average number of T2-weighted imaging lesions was similar in the three groups, in contrast with a significantly lower number of gradient-echo sequence lesions in CCM2 patients (p < 0.05). The number of gradient-echo sequence lesions increased more rapidly with age in CCM1 than in CCM2 patients (p < 0.05). INTERPRETATION: Despite similarities among the three groups, there is a significantly lower number of affected individuals in CCM3 pedigrees, CCM3 mutations may confer a higher risk for cerebral hemorrhage, particularly during childhood, and the increment of gradient-echo sequence lesions with age differs between CCM1 and CCM2 patients.

Turnover of hepatitis B virus X protein is regulated by damaged DNA-binding complex.

Mammalian hepatitis B viruses encode an essential regulatory protein, termed X, which may also be implicated in liver cancer development associated with chronic infection. X protein, also referred to as HBx in human virus and WHx in woodchuck virus, has been reported to bind to a number of cellular proteins, including the DDB1 subunit of the damaged DNA-binding (DDB) complex. Our previous work provided genetic evidence for the importance of WHx-DDB1 interaction in both the activity of the X protein and establishment of viral infection in woodchucks. In the present study, a direct action of DDB1 on the X protein is documented. Physical interaction between the two proteins leads to an increase in X protein stability. This effect results from protection of the viral protein from proteasome-mediated degradation. Protection of WHx is overcome in the presence DDB2, the second subunit of the DDB heterodimer. In keeping with observations reported for HBx, DDB2 was found to directly bind to WHx. Nonetheless, the counteracting effect of DDB2 on X stabilization requires DDB2-DDB1 interaction. Taken together, these findings substantiate the physical and functional connection between the X protein and the DDB1-DDB2 heterodimer, leading to the regulation of the pool of the viral protein.