Update on Novel CCM Gene Mutations in Patients with Cerebral Cavernous Malformations

Cerebral cavernous malformations (CCMs) are lesions affecting brain microvessels. The pathogenesis is not clearly understood. Conventional classification criterion is based on genetics, and thus, familial and sporadic forms can be distinguished; however, classification of sporadic cases with multiple lesions still remains uncertain. To date, three CCM causative genes have been identified: CCM1/KRIT1, CCM2/MGC4607 and CCM3/PDCD10. In our previous mutation screening, performed in a cohort of 95 Italian patients, with both sporadic and familial cases, we identified several mutations in CCM genes. This study represents further molecular screening in a cohort of 19 Italian patients enrolled by us in the few last years and classified into familial, sporadic and sporadic with multiple lesions cases. Direct sequencing and multiplex ligation-dependent probe amplification (MLPA) analysis were performed to detect point mutations and large genomic rearrangements, respectively. Effects of detected mutations and single-nucleotide polymorphisms (SNPs) were evaluated by an in silico approach and by western blot analysis. A novel nonsense mutation in CCM1 and a novel missense mutation in CCM2 were detected; moreover, several CCM2 gene polymorphisms in sporadic CCM patients were reported. We believe that these data enrich the mutation spectrum of CCM genes, which is useful for genetic counselling to identify both familial and sporadic CCM cases, as early as possible.     

Familial cerebral cavernous malformation: report of a further Italian family

Cerebral cavernous malformations (CCMs) are vascular abnormalities that may cause seizures, headaches, intracerebral hemorrhages, and focal neurological deficits; they can also be clinically silent and may occur as a sporadic or an autosomal dominant condition. Three genes have been identified as causing familial CCM: KRIT1/CCM1, MGC4607/CCM2, and PDCD10/CCM3, mapping, respectively, on chromosomes 7q, 7p, and 3q. This is a report on an Italian family affected by CCM due to a KRIT1 gene mutation on exon 13. The mother suffered from a cerebellar hematoma and was severely disabled; one son had suffered from intractable seizures and underwent surgery for removal of a cavernous angioma, while another son was asymptomatic. Brain MRI showed CCMs in all patients. This report underlines that a familial form of CCM could be suspected when a patient presents with multiple CCMs; neurologists and neurosurgeons should be aware that genetic testing for these forms is available.     

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.     

Clinical, magnetic resonance imaging, and genetic study of 5 Italian families with cerebral cavernous malformation

BACKGROUND: Cerebral cavernous malformations (CCMs) are congenital vascular anomalies of the central nervous system that can result in seizures, hemorrhage, recurrent headaches, and focal neurologic deficits. These CCMs can occur as sporadic or autosomal dominant conditions, although with incomplete penetrance and variable clinical expression. Three CCM loci have been identified, on chromosomes 7q21-22 (CCM1; Online Mendelian Inheritance in Man [OMIM] 116860), 7p13-15 (CCM2; OMIM 603284), and 3q25.2-27 (CCM3; OMIM 603285), and 3 genes have been cloned, KRIT1 on CCM1, MGC4607 on CCM2, and PDCD10 on CCM3. Mutations in KRIT1 account for more than 40% of CCMs. OBJECTIVE: To describe the results of a comprehensive evaluation of 5 Italian families affected with CCM. DESIGN: Clinical, magnetic resonance imaging, and KRIT1 gene analysis. SETTING: University academic teaching hospitals. PATIENTS: Fifteen patients with CCM diagnosed according to defined criteria and 45 at-risk, symptom-free relatives. RESULTS: Three novel and 2 described mutations were found in KRIT1. The families included 33 KRIT1 mutation carriers, 57.6% of whom had no symptoms. Magnetic resonance imaging revealed CCM lesions in 82.3% of symptom-free mutation carriers. CONCLUSIONS: The data confirm both incomplete clinical and neuroimaging penetrance in families with the KRIT1 mutation. This consideration is important in genetic counseling. Moreover, the data emphasize both the importance of magnetic resonance imaging in the diagnosis of CCM and the potential for DNA-based diagnosis to identify subjects at risk.     

Cerebral cavernous malformation: novel mutation in a Chinese family and evidence for heterogeneity

Familial cerebral cavernous malformation (CCM) is an autosomal dominant disorder producing vascular anomalies throughout the central nervous system associated with seizures and hemorrhagic stroke. Linkage analysis has shown evidence for at least three genetic loci underlying this disorder with a founder mutation in the Mexican/Hispanic community. We report the first family of Chinese ethnic origin with CCM having a novel mutation in the CCM1 gene. The mutation in exon 19 causes a premature stop codon (Q698X) predicted to produce a truncated Krev1 interaction-trapped 1 (KRIT1) protein. Members of the family with this mutation have a wide range in age of onset with seizures, ataxia, spinal cord vascular malformation, headaches and skin lesions. An additional unrelated sporadic subject with brain lesions compatible with CCM as well as vascular skin findings suggesting the blue rubber bleb nevus (BRBN) syndrome has no mutation detected in the CCM1 gene. These findings expand the phenotype of and demonstrate further evidence for the heterogeneity in the CCM syndrome.     

Genetic Variations Within KRIT1/CCM1, MGC4607/CCM2 and PDCD10/CCM3 in a Large Italian Family Harbouring a Krit1/CCM1 Mutation

Cerebral cavernous malformations (CCMs) are congenital vascular anomalies of the central nervous system that can result in seizures, haemorrhage, recurrent headaches and focal neurologic deficit. CCMs can occur as an autosomal dominant trait with incomplete penetrance and a wide phenotypic variability. The genes responsible for this disease are KRIT1/CCM1 on chromosome 7q21.2, MGC4607/CCM2 on chromosome 7p15–p13 and PDCD10/CCM3 on chromosome 3q25.2–q27. Mutations in KRIT1/CCM1 account for more than 40% of CCMs. We previously reported a CCM family harbouring the KRIT1/CCM1 1204delAACAA mutation. In order to search for possible explanation of the clinical variability observed, we looked for genetic variation within exons and exon/intron regions in the three genes KRIT1, MGC4607 and PDCD10 associated to the disease within this large family, 23 subjects have been analysed. Identified genetic variations in the three genes are here presented. We believe that genetic variations could interfere with the proper CCM1/CCM2/CCM3 protein complex thus explaining the observed clinical variability.     

Clinical features of cerebral cavernous malformations patients with KRIT1 mutations

Cerebral Cavernous Malformations (CCM/OMIM 604214) are vascular malformations causing seizures and cerebral hemorrhages. They occur as a sporadic and autosomal dominant condition, the latter being characterized by the presence of multiple CCM lesions. Stereotyped truncating mutations of KRIT1, the sole CCM gene identified so far, have been identified in CCM1 linked families but the clinical features associated with KRIT1 mutations have not yet been assessed in a large series of patients. We conducted a detailed clinical, neuroradiological and molecular analysis of 64 consecutively recruited CCM families segregating a KRIT1 mutation. Those families included 202 KRIT1 mutation carriers. Among the 202 KRIT1 mutation carriers, 126 individuals were symptomatic and 76 symptom-free. Mean age at clinical onset was 29.7 years (range, 2-72); initial clinical manifestations were seizures in 55% of the cases and cerebral hemorrhages in 32%. Average number of lesions on T2 weighted MRI was 4.9 (+/-7.2) and on gradient echo sequences 19.8 (+/-33.2). Twenty-six mutation carriers harbored only one lesion on T2-weighted MRI, including 4 mutation carriers, aged from 18 to 55 yr-old, who presented only one CCM lesion both on T2-weighted and on highly sensitive gradient echo MRI sequences. Five symptom free mutation carriers, aged from 27 to 48 yr-old, did not have any detectable lesion both on T2WI and gradient echo MRI sequences. Within KRIT1/CCM1 families, both clinical and radiological penetrance are incomplete and age dependent. Importantly for genetic counseling, nearly half of the KRIT1 mutation carriers aged 50 or more are symptom-free. The presence of only one lesion, even when using gradient echo MRI sequences, can be observed in some patients with an hereditary form of the disease. Incomplete neuroradiological penetrance precludes the use of cerebral MRI to firmly establish a non carrier status, even at an adult age and even when using highly sensitive gradient echo MRI. Altogether these data suggest that the hereditary nature of the disorder may be overlooked in some mutation carriers presenting as sporadic cases with a unique lesion.     

CCM1 gene mutations in families segregating cerebral cavernous malformations

Cerebral cavernous malformations (CCM) are vascular anomalies, sometimes inherited as an autosomal dominant trait, which can cause strokes and seizures. Recently, mutations of the CCM1 gene (chromosome 7q) have been found in a subset of families. The authors found 10 new mutations by screening 29 families and five seemingly sporadic cases of CCM. The mutations predicted truncation of the Krit1 mRNA encoded by CCM1, supporting the contention that CCM result from loss of Krit1 protein function and the possibility that this protein acts as a tumor suppressor.     

Vascular permeability in cerebral cavernous malformations

Patients with the familial form of cerebral cavernous malformations (CCMs) are haploinsufficient for the CCM1, CCM2, or CCM3 gene. Loss of corresponding CCM proteins increases RhoA kinase-mediated endothelial permeability in vitro, and in mouse brains in vivo. A prospective case-controlled observational study investigated whether the brains of human subjects with familial CCM show vascular hyperpermeability by dynamic contrast-enhanced quantitative perfusion magnetic resonance imaging, in comparison with CCM cases without familial disease, and whether lesional or brain vascular permeability correlates with CCM disease activity. Permeability in white matter far (WMF) from lesions was significantly greater in familial than in sporadic cases, but was similar in CCM lesions. Permeability in WMF increased with age in sporadic patients, but not in familial cases. Patients with more aggressive familial CCM disease had greater WMF permeability compared to those with milder disease phenotype, but similar lesion permeability. Subjects receiving statin medications for routine cardiovascular indications had a trend of lower WMF, but not lesion, permeability. This is the first demonstration of brain vascular hyperpermeability in humans with an autosomal dominant disease, as predicted mechanistically. Brain permeability, more than lesion permeability, may serve as a biomarker of CCM disease activity, and help calibrate potential drug therapy.     

Characterization of ataxias with magnetic resonance imaging and spectroscopy

A wide variety of autosomal transmitted ataxias exist and their ultimate characterization requires genetic testing. Common clinical characteristics among different ataxia types complicate the choice of the appropriate genetic test. Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) generally show cerebellar or cerebral atrophy and perturbed metabolite levels which differ between ataxias. In order to help the clinician accurately identify the ataxia type, reported MRI and MRS data in different brain regions are summarized for more than 60 different types of autosomal inherited and sporadic ataxias.     

中国汉族家族性脑海绵状血管瘤：1家系谱回顾分析

目的　探讨汉族人家族性脑海绵状血管瘤的临床、影像学及病理特点。方法 对1家族性脑海绵状血管瘤家系进行临床、影像学和病理分析,并绘制家系遗传图谱。结果 该家系16人共4人发病,符合常染色体显性不完全外显遗传,临床以头痛、出血、局灶性神经功能障碍为主要表现,头颅MRITlWI多呈混杂信号,T2WI多为不均匀高信号为主的混杂信号,内部可见夹杂低信号,边缘为低信号环。镜下脑海绵状血管瘤由缺乏肌层和弹力纤维的大小不等的海绵状血管窦组成,病灶内可见玻璃样变、钙化或不同阶段的出血,病灶周围可有胶质增生带,病灶内部或周围含有含铁血黄素。结论 家族性脑海绵状血管瘤是常染色体不完全显性遗传病。头颅MRIT2加权像病灶周围含铁血黄素沉积的“铁环征”,是脑海绵状血管瘤的特征性MRI表现。其病理结构是其易反复少量出血及MRI影像表现复杂多样的主要原因。     

Characteristics of cavernomas of the brain and spine

The incidence of cavernomas in the general population ranges from 0.3% to 0.5%. They frequently occur in young adults, usually being detected between the second and fifth decade of life, in both sporadic and familial forms. Patients with inherited cavernomas are typically affected by multiple lesions, whereas sporadic forms mostly present with a single lesion. Three genes responsible for development of cavernomas identified to date include CCM1, CCM2, and CCM3. The natural history of brain cavernomas is relatively benign and up to 21% of patients are asymptomatic. The most frequent manifestations of the disease are seizures, focal neurological deficits, and hemorrhage. We review the current literature data on the characteristics of brain and spinal cavernomas.     

Epileptogenic brain malformations: clinical presentation, malformative patterns and indications for genetic testing.

We review here those malformations of the cerebral cortex which are most often observed in epilepsy patients, for which a genetic basis has been elucidated or is suspected and give indications for genetic testing. There are three forms of lissencephaly (agyria-pachygyria) resulting from mutations of known genes, which can be distinguished because of their distinctive imaging features. They account for about 85% of all lissencephalies. Lissencephaly with posteriorly predominant gyral abnormality is caused by mutations of the LIS1 gene on chromosome 17. Anteriorly predominant lissencephaly in hemizygous males and subcortical band heterotopia (SBH) in heterozygous females are caused by mutations of the XLIS(or DCX) gene. Mutations of the coding region of XLIS were found in all reported pedigrees, and in most sporadic female patients with SBH. Missense mutations of both LIS1 and XLIS genes have been observed in some of the rare male patients with SBH. Autosomal recessive lissencephaly with cerebellar hypoplasia has been associated with mutations of the reelin gene. With few exceptions, children with lissencephaly have severe developmental delay and infantile spasms early in life. Patients with SBH have a mild to severe mental retardation with epilepsy of variable severity and type. X-linked bilateral periventricular nodular heterotopia (BPNH) consists of typical BPNH with focal epilepsy in females and prenatal lethality in males. About 88% of patients have focal epilepsy. Filamin A (FLNA) mutations have been reported in some families and in sporadic patients. Additional, possibly autosomal recessive gene(s) are likely to be involved in causing BPNH non-linked to FLN1. Tuberous sclerosis (TS) is a dominant disorder caused by mutations in at lest two genes, TSC1 and TSC2. 75% of cases are sporadic. Most patients with TS have epilepsy. Infantile spasms are a frequent early manifestation of TS. Schizencephaly (cleft brain) has a wide anatomo-clinical spectrum, including focal epilepsy in most patients. Familial occurrence is rare. Heterozygous mutations in the EMX2 gene have been reported in some patients. However, at present, there is no clear indication on the possible pattern of inheritance and on the practical usefulness that mutation detection in an individual with schizencephaly would carry in terms of genetic counselling. Amongst several syndromes featuring polymicrogyria, bilateral perisylvian polymicrogyria had familial occurrence on several occasions. Genetic heterogeneity is likely, including autosomal recessive, X-linked dominant, X-linked recessive inheritance and association to 22q11.2 deletions. FISH analysis for 22q11.2 is advisable in all patients with perisylvian polymicrogyria. Parents of an affected child with normal karyotype should be given up to a 25% recurrence risk.     

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.     

Clinical and genetic study of Tunisian families with genetic generalized epilepsy: contribution of <Emphasis Type="Italic">CACNA1H</Emphasis> and <Emphasis Type="Italic">MAST4</Emphasis> genes

Genetic generalized epilepsies (GGE) (childhood absence epilepsy (CAE), juvenile myoclonic epilepsy (JME) and epilepsy with generalized tonic-clonic seizures (GTCS)) are mainly determined by genetic factors. Since few mutations were identified in rare families with autosomal dominant GGE, a polygenic inheritance was suspected in most patients. Recent studies on large American or European cohorts of sporadic cases showed that susceptibility genes were numerous although their variants were rare, making their identification difficult. Here, we reported clinical and genetic characteristics of 30 Tunisian GGE families, including 71 GGE patients. The phenotype was close to that in sporadic cases. Nineteen pedigrees had a homogeneous type of GGE (JME-CAE-CGTS), and 11 combined these epileptic syndromes. Rare non-synonymous variants were selected in probands using a targeted panel of 30 candidate genes and their segregation was determined in families. Molecular studies incriminated different genes, mainly CACNA1H and MAST4. The segregation of at least two variants in different genes in some pedigrees was compatible with the hypothesis of an oligogenic inheritance, which was in accordance with the relatively low frequency of consanguineous probands. Since at least 2 susceptibility genes were likely shared by different populations, genetic factors involved in the majority of Tunisian GGE families remain to be discovered. Their identification should be easier in families with a homogeneous type of GGE, in which an intra-familial genetic homogeneity could be suspected.     

CCM molecular screening in a diagnosis context: novel unclassified variants leading to abnormal splicing and importance of large deletions

Loss of function mutations in CCM1/KRIT1, CCM2/MGC4607, and CCM3/PDCD10 gene are identified in about 95 % of familial cases of cerebral cavernous malformations and 2/3 of sporadic cases with multiple lesions. In this study, 279 consecutive index patients referred for either genetic counseling or for diagnosis of cerebral hemorrhage of unknown etiology were analyzed for the three cerebral cavernous malformations (CCM) genes by direct sequencing and quantitative studies, to characterize in more detail the mutation spectrum associated with cerebral cavernous malformations and to optimize CCM gene screening. Analysis of the cDNA was performed when possible to detect the consequences of the genomic variations. A pathogenic mutation was identified in 122 patients. CCM1 was mutated in 80 patients (65 %), CCM2 in 23 (19 %), and CCM3 in 19 (16 %). One hundred patients harbored a loss of function point mutation (82 %) and 22 had a large deletion (18 %). Novel unclassified variants were detected in the patients among whom six led to a splicing defect. The causality of three missense variants that did not modify the splicing could not be established. These findings expand the CCM mutation spectrum and highlight the importance of screening the three CCM genes with both direct sequencing and a quantitative method. In addition, six new unclassified variants were shown to be deleterious because they led to a splicing defect. This underlines the necessity of the cDNA analysis when an unknown variant is detected.     

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.     

Birth order and the genetics of amyotrophic lateral sclerosis

The cause of ALS remains largely unknown for the 90% with no known family history, but spontaneous mutation to risk alleles of as yet unidentified genes is possible. It has long been recognized that genetic diseases may be more likely to occur in the last born children of a sibship because increased paternal age is associated with an increased spontaneous point mutation rate in sperm. To test the hypothesis that such a mechanism is responsible for sporadic ALS, we have performed a retrospective analysis of birth order position. We have analyzed sibships of size greater than four using a binomial test for birth position. The 478 pedigrees studied show no birth order effect, suggesting that any genetic contributions to sporadic ALS are more likely to be through deletion in large genes or interactions of common polymorphisms, rather than frequent spontaneous point mutation. This is encouraging for the prospect of finding sporadic ALS susceptibility genes using genome-wide association mapping.     

A clinical and genetic study of familial Parkinson's disease

The clinical features of familial Parkinson's disease (PD) were investigated by examining the families of 20 British probands who were selected on the basis of having clinically typical PD and at least one affected relative. Forty-nine secondary cases were identified. These subjects were clinically indistinguishable from sporadic cases of idiopathic PD. If it is assumed that familial PD has a genetic basis, pedigree and segregation analysis suggested autosomal dominant inheritance of a gene or genes with reduced penetrance as the most likely explanation. The data did not support the possibilities of either mitochondrial or polygenic inheritance, although the latter cannot be excluded. The role of genetic factors in sporadic cases of PD remains unclear.