Mutations within the programmed cell death 10 gene cause cerebral cavernous malformations

Large germline deletions and duplication in isolated cerebral cavernous malformation patients

Cerebral cavernous malformations (CCM) are vascular lesions that predispose to headaches, seizures, and hemorrhagic stroke. Hereditary CCMs are usually associated with the occurrence of multiple CCMs and occur with a frequency of 1:2,000 to 1:10,000. In this study, eight isolated cases with multiple CCMs but no CCM1-3 point mutation were analyzed using the multiplex ligation-dependent probe amplification assay. Four genomic rearrangements were identified including a previously unreported large duplication within the CCM1 gene and a novel deletion involving the entire coding region of the CCM2 gene. Consequently, systematic screening for CCM deletions/duplications is recommended.

Two non-homologous brain diseases-related genes, SERPINI1 and PDCD10, are tightly linked by an asymmetric bidirectional promoter in an evolutionarily conserved manner

BACKGROUND

Despite of the fact that mammalian genomes are far more spacious than prokaryotic genomes, recent nucleotide sequencing data have revealed that many mammalian genes are arranged in a head-to-head orientation and separated by a small intergenic sequence. Extensive studies on some of these neighboring genes, in particular homologous gene pairs, have shown that these genes are often co-expressed in a symmetric manner and regulated by a shared promoter region. Here we report the identification of two non-homologous brain disease-related genes, with one coding for a serine protease inhibitor (SERPINI1) and the other for a programmed cell death-related gene (PDCD10), being tightly linked together by an asymmetric bidirectional promoter in an evolutionarily conserved fashion. This asymmetric bidirectional promoter, in cooperation with some cis-acting elements, is responsible for the co-regulation of the gene expression pattern as well as the tissue specificity of SERPINI1 and PDCD10.

RESULTS

While SERPINI1 is predominantly expressed in normal brain and down-regulated in brain tumors, PDCD10 is ubiquitously expressed in all normal tissues but its gene transcription becomes aberrant in different types of cancers. By measuring the luciferase activity in various cell lysates, their 851-bp intergenic sequence was shown to be capable of driving the reporter gene expression in either direction. A 175-bp fragment from nt 1 to 175 in the vicinity of PDCD10 was further determined to function as a minimal bidirectional promoter. A critical regulatory fragment, from nt 176-473 outside the minimal promoter in the intergenic region, was identified to contain a strong repressive element for SERPINI1 and an enhancer for PDCD10. These cis-acting elements may exist to help coordinate the expression and regulation of the two flanking genes.

CONCLUSION

For all non-homologous genes that have been described to be closely adjacent in the mammalian genomes, the intergenic region of the head-to-head PDCD10-SERPINI1 gene pair provides an interesting and informative example of a complex regulatory system that governs the expression of both genes not only through an asymmetric bidirectional promoter, but also through fine-tuned regulations with some cis-acting elements.

Hyperosmotic Induction of Mitogen‐Activated Protein Kinase Scaffolding

Eukaryotic cells respond to hyperosmotic conditions by expunging water from the cell, leading to cell shrinkage. This is counteracted by adaptive responses that restore cell volume and strengthen the cytoskeletal architecture. In the budding yeast Saccharomyces cerevisiae, this response is mediated primarily by the mitogen-activated protein kinase (MAPK) cascade CDC42-STE50-STE11-Pbs2-Hog1. In mammalian cells, MAPK scaffold proteins facilitate the efficiency of signaling within the cascade by placing a kinase near its substrate and also regulate the subcellular localization of the signaling. Our laboratory has discovered a scaffold that coordinates the analogous Hog1 signal in mammalian cells, termed OSM (osmosensing scaffold for MEKK3). OSM organizes a complex consisting of the small GTPase Rac, MEKK3, and MKK3 for the activation of p38 MAPK. Interactions among OSM, Rac, and MEKK3 are augmented in response to sorbitol and are also localized to membrane ruffles, sites of rapid actin turnover. Suppression of the expression of OSM or MEKK3 by RNA interference strongly inhibits the sorbitol-dependent activation of p38. Furthermore, mutations in OSM were concurrently found to cause cerebral cavernous malformations (CCM), a disease of the central nervous system characterized by thin-walled, leaky blood vessels that become hemorrhagic. Our laboratory has also demonstrated that Krit1, another gene harboring mutations that lead to CCM, binds OSM and its interaction is enhanced in response to sorbitol in a similar manner as the MEKK3-OSM interaction. This chapter describes the cell biological and biochemical methods used for assaying protein-protein interactions in live cells using fluorescence resonance energy transfer, in vitro kinase assays for MEKK3-MKK3-p38 pathway members, and gene suppression by RNA interference to study hyperosmotic stress-dependent signaling.

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.

A Novel Splicing Mutation in SLC12A3 Associated With Gitelman Syndrome and Idiopathic Intracranial Hypertension

We report a case of Gitelman syndrome (GS) in a dizygotic twin who presented at 12 years of age with growth delay, metabolic alkalosis, hypomagnesemia and hypokalemia with inappropriate kaliuresis, and idiopathic intracranial hypertension with bilateral papilledema (pseudotumor cerebri). The patient, her twin sister, and her mother also presented with cerebral cavernous malformations. Based on the early onset and normocalciuria, Bartter syndrome was diagnosed first. However, mutation analysis showed that the proband is a compound heterozygote for 2 mutations in SLC12A3: a substitution of serine by leucine at amino acid position 555 (p.Ser555Leu) and a novel guanine to cytosine transition at the 5' splice site of intron 22 (c.2633+1G>C), providing the molecular diagnosis of GS. These mutations were not detected in 200 normal chromosomes and cosegregated within the family. Analysis of complementary DNA showed that the heterozygous nucleotide change c.2633+1G>C caused the appearance of 2 RNA molecules, 1 normal transcript and 1 skipping the entire exon 22 (r.2521_2634del). Supplementation with potassium and magnesium improved clinical symptoms and resulted in catch-up growth, but vision remained impaired. Three similar associations of Bartter syndrome/GS with pseudotumor cerebri were found in the literature, suggesting that electrolyte abnormalities and secondary aldosteronism may have a role in idiopathic intracranial hypertension. This study provides further evidence for the phenotypical heterogeneity of GS and its association with severe manifestations in children. It also shows the independent segregation of familial cavernomatosis and GS.

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.

Molecular genetics of familial cerebral cavernous malformations

Cerebral cavernous malformations (CMs) are angiographically occult neurovascular lesions that consist of enlarged vascular channels without intervening normal parenchyma. Cavernous malformations can occur as sporadic or autosomal- dominant inherited conditions. Approximately 50% of Hispanic patients with cerebral CMs have the familial form, compared with 10 to 20% of Caucasian patients. There is no difference in the pathological findings or presentation in the sporadic and familial forms. To date, familial CMs have been attributed to mutations at three different loci: CCM1 on 7q21.2, CCM2 on 7p15-p13, or CCM3 on 3q25.2-q27. The authors summarize the current understanding of the molecular events underlying familial CMs.

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.

Mutations in apoptosis-related gene, PDCD10, cause cerebral cavernous malformation 3

OBJECTIVE

To identify the CCM3 gene in a population of 61 families with a positive family history of cerebral cavernous malformations (CCM), 8 of which had suggestive linkage to the CCM3 locus.

METHODS

We searched for mutations within the CCM3 interval using a high-throughput screening technique, temperature-gradient capillary electrophoresis. Mutations detected by this device were subsequently sequenced, and the results were analyzed.

RESULTS

A recent study by Bergametti et al. established Programmed Cell Death 10 (PDCD10) as the gene responsible for CCM3. We hereby confirm PDCD10 as the CCM3 gene by reporting four novel mutations in 61 CCM families. Two of these mutations were identical and produced a stop codon in exon 7. Another two resulted in frameshift mutations in exon 6, although the mutations occurred at different points along the exon. The last mutation caused a frameshift in exon 9. Of note, mutations in these families completely cosegregated with the trait. Three of the five families had prior linkage data suggestive of the CCM3 locus, whereas the remaining two were identified in index patients with a positive family history but no linkage data.

CONCLUSION

Our data establish PDCD10 as the gene responsible for CCM in families linking to the CCM3 locus. The discovery of the third gene involved in inherited forms of CCM, after KRIT1 and Malcavernin, is an important step toward dissecting the molecular pathophysiology of this disease.

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.

Update on the molecular genetics of vascular anomalies

Genetic factors play a critical role in the pathogenesis of vascular anomalies. Significant advances have been made in recent years in identifying the genetic and molecular determinants of a variety of vascular anomalies using a molecular genetic approach. Several genes for vascular anomalies have been identified. These genes include AGGF1 for Klippel-Trenaunay syndrome, RASA1 for capillary malformations, KRIT1, MGC4607, PDCD10 for cerebral cavernous malformations, glomulin for glomuvenous malformations, TIE2 for multiple cutaneous and mucosal venous malformations, VEGFR-3, FOXC2, NEMO, SOX18 for lymphedema or related syndromes, ENG, ACVRLK1, MADH4 for HHT or related syndromes, NDP for Coats' disease, Notch3 for CADASIL, and PTEN for Proteus Syndrome. These findings have made genetic testing possible in some clinical cases, and may lead to the development of therapeutic strategies for vascular anomalies. Furthermore, these studies have identified critical genes involved in vascular morphogenesis, and provided fundamental understanding of the molecular mechanisms underlying vasculogenesis and angiogenesis.

Neuronal expression of the Ccm2 gene in a new mouse model of cerebral cavernous malformations

Cerebral cavernous malformations are vascular defects of the central nervous system consisting of clusters of dilated vessels that are subject to frequent hemorrhaging. The genes mutated in three forms of autosomal dominant cerebral cavernous malformations have been cloned, but it remains unclear which cell type is ultimately responsible for the lesion. In this article we describe mice with a gene trap insertion in the Ccm2 gene. Consistent with the human phenotype, heterozygous animals develop cerebral vascular malformations, although penetrance is low. Beta-galactosidase activity in heterozygous brain and in situ hybridization in wild-type brain revealed Ccm2 expression in neurons and choroid plexus but not in vascular endothelium of small vessels in the brain. The expression pattern of Ccm2 is similar to that of the Ccm1 gene and its interacting protein ICAP1 (Itgb1bp1). These data suggest that cerebral cavernous malformations arise as a result of defects in the neural parenchyma surrounding the vascular endothelial cells in the brain.

Patterns of expression of the three cerebral cavernous malformation (CCM) genes during embryonic and postnatal brain development

Cerebral Cavernous Malformation (CCM) is a disease characterized by capillary-venous lesions mostly located in the central nervous system. It occurs both as a sporadic and hereditary autosomal dominant condition. Three CCM genes have been identified and shown to encode the KRIT1 (CCM1), MGC4607 (CCM2) and PDCD10 (CCM3) proteins whose functions are so far unknown. In an attempt to get some insight into the role of the 3 CCM genes, we used in situ hybridization to conduct a comparative analysis of their expression pattern at several time points during murine embryonic, postnatal and adult stages particularly within the central nervous system. A strong expression of the 3 Ccm genes was detected in the various neuronal cell layers of the brain, cerebellum and spinal cord, from embryonic to adult life. By E14.5 a moderate labelling was observed in the heart, arterial and venous large vessels with all 3 Ccm probes. Ccm2 and Ccm3 mRNAs, but not Ccm1, were clearly detected within meningeal and parenchymal cortical vessels at P8. This expression was no more detected by P19 and in adult murine brain, strongly suggesting a role for these 2 proteins in the intensive angiogenesis process occuring within the central nervous system during this period.

CCM2 Expression Parallels That of CCM1

Background and Purpose— Mutations in CCM2 (MGC4607 or malcavernin) cause familial cerebral cavernous malformation (CCM), an autosomal dominant neurovascular disease. Both the function of this molecule and the pathogenesis of the disease remain elusive.

Methods— We analyzed the mRNA expression of Ccm1 and Ccm2 in the embryonic and postnatal mouse brain by in situ hybridization. Subsequently, we generated CCM2-specific polyclonal antibodies and tested their specificity using transient transfection experiments in various cell lines. We then investigated CCM2 protein expression in cerebral and extracerebral tissues by Western blot analysis as well as immunohistochemistry and compared these results with CCM1 (KRIT1) protein expression.

Results— In situ analysis shows similar temporal and spatial expression patterns for Ccm1 and Ccm2, although Ccm1 expression appears more widespread. Immunohistochemical analysis shows that CCM2 is expressed in various human organs, most noticeably in the arterial vascular endothelium. As is the case with CCM1, CCM2 is not expressed in other vascular wall elements such as smooth muscle cells or the venous circulation. Within cerebral tissue, it is also expressed in pyramidal neurons, astrocytes, and their foot processes. In extracerebral tissues, CCM2 is present in various epithelial cells necessary for blood-organ barrier formation.

Conclusions— CCM1 and CCM2 have similar expression patterns during development and postnatally thereafter. Given the fact that the disease phenotypes caused by mutations in either gene are clinically and pathologically indistinguishable, the significant overlap in expression pattern supports the hypothesis that both molecules are involved in the same pathway important for central nervous system vascular development.

Genetics of cerebral cavernous malformations

The past few years have seen rapid advances in our understanding of the genetics and molecular biology of cerebral cavernous malformations (CCM). This article summarizes the recent cloning of the CCM1, CCM2, and CCM3 genes, which are responsible for autosomal dominant CCM, and also describes current hypotheses for their roles in integrin and p38 mitogen-activated protein kinase- mediated regulation of angiogenesis. A mouse model of CCM has been generated by mutation of the Ccm1 gene, and it indicates a role for that protein in arterial development. Future studies will probably focus on integration of data from each of the three CCM genes into a single model of the pathogenesis of cavernous malformation.

Cerebral venous malformations have distinct genetic origin from cerebral cavernous malformations

BACKGROUND AND PURPOSE

Pathogenesis of cerebral venous malformation (CVM) is unknown. Because of coexistence of CVM and cerebral cavernous malformations (CCM), some studies have suggested that these 2 entities share a common origin and pathogenetic mechanism.

METHODS

We have identified and ascertained over 200 families with CCM. Among these, 1 unique family was found to have members affected by both disorders. We have performed mutational analysis in all 3 CCM genes, KRIT1, Malcavernin, and PDCD10, to identify the causative gene in the family.

RESULTS

Mutational analysis revealed a frameshift mutation affecting exon 19 of the CCM1 gene (KRIT1) in members with CCM, whereas no such mutation was observed in the member with CVM.

CONCLUSIONS

These findings support the hypothesis that CVM and CCM are 2 distinct entities with different pathogenetic mechanisms. This data further supports the hypothesis that CVM has a distinct biology and clinical behavior when compared to CCM. CVM is a benign developmental anomaly and should be managed separately from CCM.

CCM1 and CCM2 protein interactions in cell signaling: implications for cerebral cavernous malformations pathogenesis

Cerebral cavernous malformations (CCMs) are sporadically acquired or inherited vascular lesions of the central nervous system consisting of clusters of dilated thin-walled blood vessels that predispose individuals to seizures and stroke. Familial CCM is caused by mutations in KRIT1 (CCM1) or in malcavernin (CCM2), the murine ortholog of which was concurrently characterized as osmosensing scaffold for MEKK3 (OSM). The roles of the CCM proteins in the pathogenesis of the disorder remain largely unknown. Here, we use co-immunoprecipitation, fluorescence resonance energy transfer and subcellular localization strategies to show that the CCM1 gene product, KRIT1, interacts with the CCM2 gene product, malcavernin/OSM. Analogous to the established interactions of CCM1 and beta1 integrin with ICAP1, the CCM1/CCM2 association is dependent upon the phosphotyrosine binding (PTB) domain of CCM2. A familial CCM2 missense mutation abrogates the CCM1/CCM2 interaction, suggesting that loss of this interaction may be critical in CCM pathogenesis. CCM2 and ICAP1 bound to CCM1 via their respective PTB domains differentially influence the subcellular localization of CCM1. Furthermore, we expand upon the established involvement of CCM2 in the p38 mitogen-activated protein kinase signaling module by demonstrating that CCM1 associates with CCM2 and MEKK3 in a ternary complex. These data indicate that the genetic heterogeneity observed in familial CCM may reflect mutation of different molecular members of a coordinated signaling complex.

Biomedicine and diseases: the Klippel-Trenaunay syndrome, vascular anomalies and vascular morphogenesis

Vascular morphogenesis is a vital process for embryonic development, normal physiologic conditions (e.g. wound healing) and pathological processes (e.g. atherosclerosis, cancer). Genetic studies of vascular anomalies have led to identification of critical genes involved in vascular morphogenesis. A susceptibility gene, VG5Q (formally named AGGF1), was cloned for Klippel-Trenaunay syndrome (KTS). AGGF1 encodes a potent angiogenic factor, and KTS-associated mutations enhance angiogenic activity of AGGF1, defining 'increased angiogenesis' as one molecular mechanism for the pathogenesis of KTS. Similar studies have identified other genes involved in vascular anomalies as important genes for vascular morphogenesis, including TIE2, VEGFR-3, RASA1, KRIT1, MGC4607, PDCD10, glomulin, FOXC2, NEMO, SOX18, ENG, ACVRLK1, MADH4, NDP, TIMP3, Notch3, COL3A1 and PTEN. Future studies of vascular anomaly genes will provide insights into the molecular mechanisms for vascular morphogenesis, and may lead to the development of therapeutic strategies for treating these and other angiogenesis-related diseases, including coronary artery disease and cancer.

Genes contributing to risk for common forms of stroke

The quest for disease genes that confer risk for stroke is now being undertaken using three complementary approaches. Positional cloning using rare Mendelian phenocopies of stroke has found genes that contribute to rare forms of stroke but, so far, not to the common forms of stroke. Candidate-gene case-control association studies using the common forms of stroke have found suggestive associations of modest effect. However, positional cloning using hundreds of Icelandic families affected by the common forms of stroke has recently found two genes conferring substantial risk for ischemic stroke that have apparently been confirmed in the USA and other European populations. Both genes encode enzymes, phosphodiesterase 4D (PDE4D) and arachidonate 5-lipoxygenase-activating protein (FLAP), which suggest novel treatment strategies for stroke prevention.