CCM3 mutations are uncommon in cerebral cavernous malformations

Pediatric Cerebral Cavernous Malformations

Cerebral cavernous malformations are the second most common vascular malformations in the central nervous system, and over one-third are found in children. Lesions may be solitary or multiple, be discovered incidentally, be sporadic, or be secondary to familial cavernomatosis or radiation therapy. Children may present with focal seizures, intracranial hemorrhage, or focal neurological deficits without radiological evidence of recent hemorrhage. We present several children with cerebral cavernous malformations and explore the challenges of their diagnosis in children, their key imaging features, the role of follow-up imaging, and their subsequent management including stereotactic radiosurgery and microsurgical resection. Individual patient risk stratification is advocated for all affected children and their families.

Dual function of programmed cell death 10 (PDCD10) in drug resistance

Drug resistance, a major challenge in cancer chemotherapy, is a result of several mechanistic alterations including resistance to apoptosis. Apoptosis is a well-controlled cell death mechanism which is regulated by several signaling pathways. Alterations in structure, function, and expression pattern of the proteins involved in the regulation of apoptosis have been linked to drug resistance. Programmed Cell Death 10 (PDCD10) protein is recently associated with the regulation of cell survival and apoptosis. However, the role of PDCD10 in drug resistance has not been clearly established. Here, we aimed to figure out the role of PDCD10 in resistance to anti-cancer agents in different cell lines. We found that PDCD10 expression was cell- and anti-cancer agent-specific; down-regulated in doxorubicin- and docetaxel-resistant MCF7 cells while up-regulated in doxorubicin-resistant HeLa cells. Down-regulation of PDCD10 expression by siRNA in parental MCF7 cells increased the resistance while it increased sensitivity in doxorubicin-resistant HeLa cells. Similarly, over-expression of PDCD10 in parental HeLa cells increased the resistance to doxorubicin while it re-sensitized doxorubicin-resistant MCF7 cells. Moreover, the alterations in PDCD10 expression led to changes in caspase 3/7 activity and the levels of apoptosis-related genes. Our results point out a possible dual role of PDCD10 in drug resistance for the first time in the literature and emphasize PDCD10 as a novel target for reversal of drug resistance in cancer.

PDCD10 gene mutations in multiple cerebral cavernous malformations

Cerebral cavernous malformations (CCMs) are vascular abnormalities that may cause seizures, intracerebral haemorrhages, and focal neurological deficits. Familial form shows an autosomal dominant pattern of inheritance with incomplete penetrance and variable clinical expression. Three genes have been identified causing familial CCM: KRIT1/CCM1, MGC4607/CCM2, and PDCD10/CCM3. Aim of this study is to report additional PDCD10/CCM3 families poorly described so far which account for 10-15% of hereditary cerebral cavernous malformations. Our group investigated 87 consecutive Italian affected individuals (i.e. positive Magnetic Resonance Imaging) with multiple/familial CCM through direct sequencing and Multiplex Ligation-Dependent Probe Amplification (MLPA) analysis. We identified mutations in over 97.7% of cases, and PDCD10/CCM3 accounts for 13.1%. PDCD10/CCM3 molecular screening revealed four already known mutations and four novel ones. The mutated patients show an earlier onset of clinical manifestations as compared to CCM1/CCM2 mutated patients. The study of further families carrying mutations in PDCD10/CCM3 may help define a possible correlation between genotype and phenotype; an accurate clinical follow up of the subjects would help define more precisely whether mutations in PDCD10/CCM3 lead to a characteristic phenotype.

CCM3 Mutations Are Associated with Early-Onset Cerebral Hemorrhage and Multiple Meningiomas

Mutations of CCM3/PDCD10 cause 10-15% of hereditary cerebral cavernous malformations. The phenotypic characterization of CCM3-mutated patients has been hampered by the limited number of patients harboring a mutation in this gene. This is the first report on molecular and clinical features of a large cohort of CCM3 patients. Molecular screening for point mutations and deletions was used to identify 54 CCM3-mutated index patients. Age at referral and clinical onset, type of inaugural events and presence of extra-axial lesions were investigated in these 54 index patients and 22 of their mutated relatives. Mean age at clinical onset was 23.0 ± 16 years. Clinical onset occurred before 10 years in 26% of the patients, and cerebral hemorrhage was the initial presentation in 72% of these patients. Multiple extra-axial, dural-based lesions were detected in 7 unrelated patients. These lesions proved to be meningiomas in 3 patients who underwent neurosurgery and pathological examination. This 'multiple meningiomas' phenotype is not associated with a specific CCM3 mutation. Hence, CCM3 mutations are associated with a high risk of early-onset cerebral hemorrhage and with the presence of multiple meningiomas.

Small deletion at the 7q21.2 locus in a CCM family detected by real-time quantitative PCR

Cerebral cavernous malformations (CCMs) represent a common autosomal dominant disorder that predisposes patients to haemorrhagic strokes and focal neurological signs. About 56% of the hereditary forms of CCMs have been so far associated with mutations in the KRIT1 (Krev Interaction Trapped 1) gene, located at 7q21.2 (CCM1 locus). We described the complete loss of 7q21.2 locus encompassing the KRIT1 gene and 4 flanking genes in a CCM family by using a dense set of 12 microsatellite markers. The complete loss of the maternal copy of KRIT1 gene region was confirmed by Real-Time Quantitative Polymerase Chain Reaction (RT-QPCR) and the same approach was used for expression analysis. Additional RT-QPCR analysis showed the extension of the deletion, for a total of 700 kb, to the adjacent downstream and upstream-located genes, MTERF, AKAP9, CYP51A1, as well as a partial loss of the ANKIB1 gene. Here we report the molecular characterization of an interstitial small genomic deletion of the 7q21.2 region in a CCMs affected family, encompassing the KRIT1 gene. Our findings confirm the loss of function mechanism for the already known CCM1 locus, without any evident involvement of the other deleted genes. Moreover, our investigations highlight the usefulness of the RT-QPCR to the molecular characterization of the breakpoints genomic deletions and to the identification of internal deleted genes involved in the human genetic diseases.

CCM3 signaling through sterile 20-like kinases plays an essential role during zebrafish cardiovascular development and cerebral cavernous malformations

Cerebral cavernous malformation is a common human vascular disease that arises due to loss-of-function mutations in genes encoding three intracellular adaptor proteins, cerebral cavernous malformations 1 protein (CCM1), CCM2, and CCM3. CCM1, CCM2, and CCM3 interact biochemically in a pathway required in endothelial cells during cardiovascular development in mice and zebrafish. The downstream effectors by which this signaling pathway regulates endothelial function have not yet been identified. Here we have shown in zebrafish that expression of mutant ccm3 proteins (ccm3Delta) known to cause cerebral cavernous malformation in humans confers cardiovascular phenotypes identical to those associated with loss of ccm1 and ccm2. CCM3Delta proteins interacted with CCM1 and CCM2, but not with other proteins known to bind wild-type CCM3, serine/threonine protein kinase MST4 (MST4), sterile 20-like serine/threonine kinase 24 (STK24), and STK25, all of which have poorly defined biological functions. Cardiovascular phenotypes characteristic of CCM deficiency arose due to stk deficiency and combined low-level deficiency of stks and ccm3 in zebrafish embryos. In cultured human endothelial cells, CCM3 and STK25 regulated barrier function in a manner similar to CCM2, and STKs negatively regulated Rho by directly activating moesin. These studies identify STKs as essential downstream effectors of CCM signaling in development and disease that may regulate both endothelial and epithelial cell junctions.

Angiotensin-converting enzyme insertion/deletion gene polymorphism in patients with familial multiple cerebral cavernous malformations

Cavernous malformations can occur in both sporadic and autosomal dominant forms. The aim of this study was to investigate the potential role of insertion/deletion (I/D) polymorphisms of the angiotensin-converting enzyme (ACE) gene in the development of cerebral cavernous malformations (CCM). Forty-one members of two families affected by familial CCM were included in this study. DNA was isolated from peripheral venous blood, and polymerase chain reaction analysis was used to detect I/D polymorphisms of the ACE gene, using HACE3s and HACE3as as primers. Only 10 participants had MRI-confirmed CCM. Of these 10 subjects, seven had the I/D, two had the D/D, and one had the I/I genotype. Of the remaining 31 subjects, 14 had the I/I, 13 had the I/D, and four had the D/D genotype. There was a greater proportion of subjects with the D allele among those with MRI-confirmed CCM than among those without (p<0.05). These results suggest that the D polymorphism of the ACE gene may be involved in the pathogenesis of familial CCM.

Paediatric presentation of familial cerebral cavernoma

We report the case of a 13-year-old male who presented with headaches and was presumed to have a brain tumour. He was subsequently found to have multiple cerebral cavernomas with haemorrhage and positive family history. We review the literature on familial cavernomas. Cerebral cavernous malformations (CCMs) are characterized by abnormally enlarged capillary cavities without intervening brain parenchyma [Verlaan et al. Neurology 2005; 65:1982-1983] that may involve any part of the central nervous system. Focal neurologic deficit and haemorrhage occur in 45% of children, higher than in adults [Stoeter. Neurosurg Rev 2001; 24]. Paediatric patients with symptomatic cavernous malformations should be treated surgically because of the risk of haemorrhage [Lee et al. Child's Nervous Syst 2008; 24:321-327].

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.

Cerebral cavernous malformations: somatic mutations in vascular endothelial cells

OBJECTIVE

Germline mutations in 3 genes have been found in familial cases of cerebral cavernous malformations (CCMs). We previously discovered somatic and germline truncating mutations in the KRIT1 gene, supporting the "2-hit" mechanism of CCM lesion formation in a single lesion. The purpose of this study was to screen for somatic, nonheritable mutations in 3 more lesions from different patients and identify the cell type(s) in which somatic mutations occur.

METHODS

Somatic mutations were sought in DNA from 3 surgically excised, fresh-frozen CCM lesions by cloning and screening polymerase chain reaction products generated from KRIT1 or PDCD10 coding regions. Laser capture microdissection was used on isolated endothelial and nonendothelial cells to determine whether somatic mutations were found in endothelial cells.

RESULTS

CCM lesions harbor somatic and germline KRIT1 mutations on different chromosomes and are therefore biallelic. Both mutations are predicted to truncate the protein. The KRIT1 somatic mutations (novel c.1800delG mutation and previously identified 34 nucleotide deletion) in CCMs from 2 different patients were found only in the vascular endothelial cells lining caverns. No obvious somatic mutations were identified in the 2 other lesions; however, the results were inconclusive, possibly owing to the technical limitations or the fact that these specimens had a small proportion of vascular endothelial cells lining pristine caverns.

CONCLUSION

The "2-hit" mechanism occurs in vascular endothelial cells lining CCM caverns from 2 patients with somatic and Hispanic-American KRIT1 germline mutations. Methods for somatic mutation detection should focus on vascular endothelial cells lining pristine caverns.

c-Myc regulates the coordinated transcription of brain disease-related PDCD10-SERPINI1 bidirectional gene pair

Two brain disease-related genes, one coding for the protease inhibitor SERPINI1 which is down-regulated in brain tumors, and the other for the PDCD10 programmed cell death gene which is often mutated in cerebral cavernous malformation, are closely adjacent in a head-to-head configuration and separated by only 851 bp on human chromosome 3q26. The 851-bp intergenic region contains a GC-rich 175-bp minimal bidirectional promoter which is essential for transcriptional activation of the two flanking genes. The oncogenic c-Myc transcription factor was identified to bind to a non-canonical E-box element (5'-CATGCG-3') of the minimal bidirectional promoter to drive both gene expressions. Methylation at the specific C nucleotide within the E-box sequence (5'-CATG(m)CG-3'), however, would severely interfere with the binding of c-Myc to the E-box. These results suggest that c-Myc plays an important role in regulating the coordinated transcription of the PDCD10-SERPINI1 bidirectional gene pair, and is possibly involved in differential expressions of these two neighboring genes in central nervous system diseases such as brain cancer.

Apoptotic functions of PDCD10/CCM3, the gene mutated in cerebral cavernous malformation 3

BACKGROUND AND PURPOSE

Mutations in the Programmed Cell Death 10 (PDCD10) gene cause autosomal dominant familial cerebral cavernous malformations (CCM3). To date, little is known about the function of this gene and its role in disease pathogenesis.

METHODS

We examined the effects of overexpression of wild-type and 2 human disease-causing variants of PDCD10 on cell death using 3 different methods (TUNEL and MTT assays and caspase-3 activation). We analyzed expression of CCM3, activated caspase-3, and p38 in endothelial cell lines using the serum deprivation model of apoptosis induction. Finally, we assayed the effects of siRNA-mediated inhibition of endogenous PDCD10 expression on cell death in endothelial cell cultures.

RESULTS

Overexpression of wild-type CCM3, but not disease-linked mutant forms, induced apoptosis as confirmed by TUNEL and increased levels of activated caspase-3. Serum starvation of endothelial cells, an inducer of apoptosis, led to increased expression of CCM3 and activation of p38 and ultimately activated caspase-3. siRNA-mediated inhibition of CCM3 expression resulted in decreased levels of p38 and activated caspase-3, and decreased cell death.

CONCLUSIONS

CCM3 is both necessary and sufficient to induce apoptosis in vitro in well-defined cell culture systems. Even though it is currently unclear whether this effect on apoptosis is direct or indirect through modulation of cell cycle, these results led to the novel hypothesis that CCM lesions may form as a consequence of aberrant apoptosis, potentially altering the balance between the endothelium and neural cells within the neurovascular unit.

Identification of an Arg35X mutation in the PDCD10 gene in a patient with cerebral and multiple spinal cavernous malformations

Although cerebral cavernous malformations (CCMs) are not uncommon, the concurrent finding of cavernous malformations (CMs) both in the brain and spinal cord is quite rare. Furthermore, multiple spinal cord CMs are extremely rare with only a few cases being reported thus far. Recently, we encountered a 33-year-old Korean male with both CCM and multiple spinal intramedullary CMs. The patient complained of seizure and right chest paresthesia. The lesions were located throughout the neuraxis including the cerebral hemisphere, brain stem, and cervical and thoracic spinal cords. Molecular analysis of the KRIT1 (CCM1), CCM2, and PDCD10 (CCM3) genes identified a heterozygous nonsense mutation (c.103C>T; Arg35X) in the PDCD10 gene, which was reported previously in a CCM family. The patient denied a family history, however, his daughter had an identical mutation, but was asymptomatic. Three months later, after identifying the mutation in the father and the daughter, the daughter presented with seizure. To the best of our knowledge, this is the first report of an association between a mutation in the PDCD10 gene and spinal CMs.

[Contribution of molecular genetics in cavernous angiomas]

In 20% of cases, central nervous system cavernomas are an autosomal dominant familial disease. In these cases, lesions are multiple and one or more parents suffer of the same affection. Three genes (CCM 1, 2 and 3) have been identified since 1999, two on chromosome 7 (one on each arm) and one on the short arm of chromosome 3. The role of these genes in normal cerebral angiogenesis is unknown today. In clinical practice, molecular tests may be useful in some situations: 1) in sporadic cases with a unique lesion, molecular test should not be performed since these cases are not genetic; 2) in patients with multiple lesions who have an affected relative, the genetic nature of the disease is obvious and molecular tests are useful only for genetic counseling; 3) in sporadic cases with multiple lesions and no known affected relative, molecular tests can establish the genetic nature of the disease and be useful for genetic counseling.

PDCD10 interacts with Ste20-related kinase MST4 to promote cell growth and transformation via modulation of the ERK pathway

PDCD10 (programmed cell death 10, TFAR15), a novel protein associated with cell apoptosis has been recently implicated in mutations associated with Cerebral Cavernous Malformations (CCM). Yeast two-hybrid screening revealed that PDCD10 interacts with MST4, a member of Ste20-related kinases. This interaction was confirmed by coimmunoprecipitation and colocalization assays in mammalian cells. Furthermore, the co-overexpression of PDCD10 and MST4 promoted cell proliferation and transformation via modulation of the extracellular signal-regulated kinase (ERK) pathway. Potent short interfering RNAs (siRNAs) against PDCD10 (siPDCD10) and MST4 (siMST4) were designed to specifically inhibit the expression of PDCD10 and MST4 mRNA, respectively. The induction of siPDCD10 or siMST4 resulted in decreased expression of endogenous PDCD10 or MST4, which was accompanied by reduced ERK activity and attenuated cell growth and anchorage-independent growth. On the other hand, siMST4 had similar effects in PDCD10-overexpressed cells. And more importantly, we confirmed that either overexpressing or endogenous PDCD10 can increase the MST4 kinase activity in vitro. Our results demonstrated that PDCD10 modulation of ERK signaling was mediated by MST4, and PDCD10 could be a regulatory adaptor necessary for MST4 function, suggesting a link between cerebral cavernous malformation pathogenesis and the ERK-MAPK cascade via PDCD10/MST4.

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.

Study of cerebral cavernous malformation in Spain and Portugal: high prevalence of a 14 bp deletion in exon 5 of MGC4607 (CCM2 gene)

OBJECTIVE

We aimed to study clinical, radiological and molecular genetic features of patients with cerebral cavernous malformations (CCMs) from the Iberian Peninsula.

METHODS

We screened Krit1(CCM1), MGC4607(CCM2), and PDCD10(CCM3) by systematic SSCP and direct sequencing of coding exons in 48 nuclear families and 30 sporadic cases of CCM from Spain and Portugal.

RESULTS

Screening of CCM patients detected nine different mutations in 19 families. We found four new mutations in Krit1. Three of them were caused by either a small insertion or deletion, which lead to frameshift and premature termination codons. We also found a missense L308H mutation located in a highly conserved sequence within the ankyrin domain of Krit1. In CCM2, we found a redundant 14 bp deletion in exon 5 of MGC4607 which predicts a truncated protein at residue 230. We did not find mutations in CCM3.

CONCLUSIONS

Finding that the 14 bp deletion was present in eleven families from the Iberian Peninsula indicates a high prevalence of this mutation. This redundant CCM2 mutation is worth considering in molecular diagnosis and genetic counselling of cerebral cavernous malformations.

Spectrum of genotype and clinical manifestations in cerebral cavernous malformations

OBJECTIVE

Cerebral cavernous malformations (CCMs) are focal dysmorphic blood vessel anomalies predisposing individuals to hemorrhagic stroke and epilepsy. CCMs are sporadic or inherited as autosomal dominant disease with three known genes. The hypothesis that genetic heterogeneity would account for the remarkable variability in CCM manifestations was tested.

METHODS

CCM cases were prospectively enrolled. Germline CCM1 gene mutations were sought in 89 CCM samples. Associations with clinical manifestations and lesion characteristics were made among 41 symptomatic familial cases, including one cohort of 26 cases with CCM1 mutations and a second cohort of 15 cases without identifiable CCM1 mutations. The 15 cases were screened for CCM2 and CCM3 mutations.

RESULTS

CCM1 mutations were found in 34 out of 50 subjects with familial disease and in none of 39 sporadic CCM cases. CCM2 and CCM3 mutations were found in three out of 10 families screened without CCM1 mutations. Clinical manifestations in 22 Hispanic-American cases with identical CCM1 mutations were highly variable. Fewer CCM1 patients experienced hemorrhage than others with familial disease (P = 0.0139 for all cases and P = 0.0442 for symptomatic cases). Adjusting for sex and age improved the logistic regression model, suggesting decreased numbers of patients with hemorrhage in CCM1 familial disease (P = 0.003 for all cases and P = 0.014 for symptomatic cases). Hemorrhage differences were not related to size or number of lesions.

CONCLUSION

Factors in addition to CCM1 germline mutation contribute to CCM clinical manifestations. However, this evidence suggests that familial cases with CCM1 mutations may have less severe clinical manifestations than other familial cases.

Deletions in CCM2 are a common cause of cerebral cavernous malformations

Cerebral cavernous malformations (CCMs) are vascular abnormalities of the brain that can result in a variety of neurological disabilities, including hemorrhagic stroke and seizures. Mutations in the gene KRIT1 are responsible for CCM1, mutations in the gene MGC4607 are responsible for CCM2, and mutations in the gene PDCD10 are responsible for CCM3. DNA sequence analysis of the known CCM genes in a cohort of 63 CCM-affected families showed that a high proportion (40%) of these lacked any identifiable mutation. We used multiplex ligation-dependent probe analysis to screen 25 CCM1, -2, and -3 mutation-negative probands for potential deletions or duplications within all three CCM genes. We identified a total of 15 deletions: 1 in the CCM1 gene, 0 in the CCM3 gene, and 14 in the CCM2 gene. In our cohort, mutation screening that included sequence and deletion analyses gave disease-gene frequencies of 40% for CCM1, 38% for CCM2, 6% for CCM3, and 16% with no mutation detected. These data indicate that the prevalence of CCM2 is much higher than previously predicted, nearly equal to CCM1, and that large genomic deletions in the CCM2 gene represent a major component of this disease. A common 77.6-kb deletion spanning CCM2 exons 2-10 was identified, which is present in 13% of our entire CCM cohort. Eight probands exhibit an apparently identical recombination event in the CCM2 gene, involving an AluSx in intron 1 and an AluSg distal to exon 10. Haplotype analysis revealed that this CCM2 deletion occurred independently at least twice in our families. We hypothesize that these deletions occur in a hypermutable region because of surrounding repetitive sequence elements that may catalyze the formation of intragenic deletions.

CCM1 gene deletion identified by MLPA in cerebral cavernous malformation

Familial cerebral cavernous malformations (CCMs) occur with a frequency of 1 in 2000 and may cause recurrent headaches, seizures, and hemorrhagic stroke. Exon-scanning-based methods have identified intragenic mutations in three genes, CCM1, CCM2, and CCM3, in about 70% of familial CCM. To date, only two large CCM2 and a single large CCM3 deletion have been published. In addition to direct sequencing of all three CCM genes, we applied a newly developed multiplex ligation-dependent probe amplification gene dosage assay (MLPA) designed to detect genomic CCM1-3 deletions/duplications. Direct sequencing did not reveal a mutation in the index case who presented with multiple CCMs that had caused a generalized tonic-clonic seizure with Todd's paralysis and headaches at the age of 5. In contrast, MLPA analyses detected a large deletion involving the entire CCM1 coding region in the proband and further affected members of this German CCM family. The MLPA results were corroborated by analyses of single nucleotide polymorphisms (SNPs) within the CCM1 gene. Thus, we here present the first report on a CCM1 gene deletion. Our results confirm a loss-of-function mutation mechanism for CCM1 and demonstrate that the use of MLPA enables a higher CCM mutation detection rate which is crucial for predictive testing of at-risk relatives.

Clinical impact of CCM mutation detection in familial cavernous angioma

INTRODUCTION AND BACKGROUND

A 3-year-old Bosnian girl with a large symptomatic brainstem and multiple supratentorial cavernous angiomas, who underwent neurosurgical treatment, is presented. As multiple cavernomas are more common in familial cases, genetic analyses and neuroradiological imaging were performed in the patient and her parents to see whether there was any evidence for inheritance. This information is important for genetic counseling and provision of medical care for at-risk relatives. Currently, no recommendation is available on how to manage these cases.

RESULTS

Genetic analyses demonstrated a novel CCM1 frameshift mutation (c.1683_1684insA; p.V562SfsX6) in the child and the asymptomatic 27-year-old mother. Sensitive gradient-echo magnetic resonance imaging of the mother revealed multiple supratentorial lesions, whereas analogous imaging of the father showed no pathological findings.

CONCLUSION

This case exemplifies that seemingly sporadic cases with multiple lesions might well be hereditary and that presymptomatic genetic testing of family members may identify relatives for whom clinical and neuroradiological monitoring is indicated.

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.

Identification of two novel mutations and of a novel critical region in the KRIT1 gene

Cerebral cavernous malformations (CCMs) represent a common autosomal dominant disorder that predisposes patients to hemorrhagic strokes and focal neurological signs. Mutations in three genes (KRIT1, MGC4607, and PDCD10) have been associated with CCMs. We investigated the role of two new mutations in the KRIT1 gene in two Italian families affected by CCMs. Whole blood DNA was extracted and the mutations were detected after polymerase chain reaction (PCR), denaturing high-performance liquid chromatography screening, and sequencing of the coding regions of the three CCMs-associated genes. Total RNA was extracted, and the KRIT1 cDNA was sequenced and subsequently subjected to real-time quantitative PCR in order to examine the translational outcome of each genomic mutation. A novel splicing acceptor site deletion of the exon 14 in one family and an intronic nucleotide change close to the exon 19 in the other one were identified, both in the KRIT1 gene. These mutations were proven to alter the correct splicing mechanism, resulting, respectively, in a truncated protein of 432 amino acids and in a protein lacking an internal segment. We report two novel cases of splicing affecting genomic variants, suggesting a careful reanalysis of previously identified splice site variations in KRIT1 to look for their possible causative roles of similar missplicing events and their consequent involvement in the pathogenesis of CCMs. Moreover, our genotype-phenotype functional correlation suggests that the C-terminal portion of the KRIT1 protein is likely to contain a short, previously unrecognized segment necessary for its activity.

Cerebral cavernous malformations: clinical insights from genetic studies

✓ Familial disease is responsible for one third to one half of cerebral cavernous malformation (CCM) cases presenting to clinical attention. Much has been learned in the past decade about the genetics of these cases, which are all inherited in an autosomal dominant pattern, at three known chromosome loci. Unique features of inherited CCMs in Hispanic-Americans of Mexican descent have been described. The respective genes for each locus have been identified and preliminary observations on disease pathways and mechanisms are coming to light, including possible explanations for selectivity of neural milieu and relationships to endothelial layer abnormalities. Mechanisms of lesion genesis in cases of genetic predisposition are being investigated, with evidence to support a two-hit model emerging from somatic mutation screening of the lesions themselves and from lesion formation in transgenic murine models of the disease. Other information on potential inflammatory factors has emerged from differential gene expression studies. Unique phenotypic features of solitary versus familial cases have emerged: different associations with venous developmental anomaly and the exceptionally high penetrance rates that are found in inherited cases when high-sensitivity screening is performed with gradient echo magnetic resonance imaging. This information has changed the landscape of screening and counseling for patients and their families, and promises to lead to the development of new tools for predicting, explaining, and modifying disease behavior.

Cerebral cavernous malformation: new molecular and clinical insights

Cerebral cavernous malformation (CCM) is a vascular malformation causing neurological problems, such as headaches, seizures, focal neurological deficits, and cerebral haemorrhages. CCMs can occur sporadically or as an autosomal dominant condition with variable expression and incomplete penetrance. Familial forms have been linked to three chromosomal loci, and loss of function mutations have been identified in the KRIT1/CCM1, MGC4607/CCM2, and PDCD10/CCM3 genes. Recently, many new pieces of data have been added to the CCM puzzle. It has been shown that the three CCM genes are expressed in neurones rather than in blood vessels. The interaction between CCM1 and CCM2, which was expected on the basis of their structure, has also been proven, suggesting a common functional pathway. Finally, in a large series of KRIT1 mutation carriers, clinical and neuroradiological features have been characterised. These data should lead to more appropriate follow up, treatment, and genetic counselling. The recent developments will also help to elucidate the precise pathogenic mechanisms leading to CCM, contributing to a better understanding of normal and pathological angiogenesis and to the development of targeted treatment.