Identification of a Novel Deletion Mutation (c.1780delG) and a Novel Splice-Site Mutation (c.1412-1G>A) in the CCM1/KRIT1 Gene Associated with Familial Cerebral Cavernous Malformation in the Chinese Population

Molecular genetic features and clinical manifestations in Chinese familial cerebral cavernous malformation: from a novel KRIT1/CCM1 mutation (c.1119dupT) to an overall view

Cerebral cavernous malformations (CCMs) are common vascular anomaly diseases in the central nervous system associated with seizures, cerebral microbleeds, or asymptomatic mostly. CCMs can be classified as sporadic or familial, with familial cerebral cavernous malformations (fCCMs) being the autosomal dominant manner with incomplete penetrance. Germline mutations of KRIT1, CCM2, and PDCD10 are associated with the pathogenesis of fCCMs. Till now, little is known about the fCCMs mutation spectrum in the Han Chinese population. In this study, we enrolled a large, aggregated family, 11/26 of the family members were diagnosed with CCMs by pathological or neuroradiological examination, with a high percentage (5/9) of focal spinal cord involvement. Genomic DNA sequencing verified a novel duplication mutation (c.1119dupT, p.L374Sfs*9) in exon 9 of the Krev interaction trapped 1 (KRIT1) gene. The mutation causes a frameshift and is predicted to generate a truncated KRIT1/CCM1 protein of 381 amino acids. All our findings confirm that c.1119dupT mutation of KRIT1 is associated with fCCMs, which enriched the CCM genes' mutational spectrum in the Chinese population and will be beneficial for deep insight into the pathogenesis of Chinese fCCMs. Additionally, with a retrospective study, we analyzed the molecular genetic features of Chinese fCCMs, most of the Chinese fCCMs variants are in the KRIT1 gene, and all these variants result in the functional deletion or insufficiency of the C-terminal FERM domain of the KRIT1 protein.

KRIT1 Gene in Patients with Cerebral Cavernous Malformations: Clinical Features and Molecular Characterization of Novel Variants

Cerebral cavernous malformations (CCMs) are vascular malformations that may result in headaches, seizures, focal neurological deficits, and hemorrhage. CCMs occur sporadically (80%) or in familial form (20%), with autosomal dominant inheritance. Among the three CCM-related genes, mutations in KRIT1 account for 53–65% of familial cases and more than 100 different mutations have been identified so far. In the present work, we describe the clinical, neuroradiological, and genetic findings of sixteen CCM Italian patients, 13 belonging to 4 unrelated families and 3 sporadic cases. Six distinct KRIT1 gene variants, two novel (c.1730+1_1730+3del, c.1664 C>T) and four previously described (c.966G>A, c.1255-1G>A c.1197_1200del, c.1255-1_1256del), were identified, including a possible de novo mutation. All the variants resulted in a premature stop codon. Cerebral 1.5 T magnetic resonance imaging showed multiple CCMs in all the mutation carriers for whom it was available, including sporadic cases. One patient had also cutaneous angiomas. Among the mutation carriers, symptomatic patients constituted 66% and a variable phenotypic expression was observed. Our data confirms phenotypic variability and incomplete penetrance of neurological symptoms in KRIT1-positive families, expands the mutational spectrum of this gene, and highlights how sporadic cases with multiple lesions need an approach similar to individuals with familial CCM.

Improving clinical interpretation of five KRIT1 and PDCD10 intronic variants

Cerebral cavernous malformation (CCM) is a vascular malformation of the central nervous system which may occur sporadically or segregate within families due to heterozygous variants in KRIT1/CCM1, MGC4607/CCM2 or PDCD10/CCM3. Intronic variants are not uncommon in familial CCM, but their clinical interpretation is often hampered by insufficient data supporting in silico predictions. Here, the mRNA analysis for two intronic unpublished variants (KRIT1 c.1147-7 T > G and PDCD10 c.395 + 2 T > G) and three previously published variants in KRIT1 but without data supporting their effects was carried out. This study demonstrated that all variants can induce a frameshift with the lack of residues located in the C-terminal regions and involved in protein-protein complex formation, which is essential for vascular homeostasis. These results support the introduction of mRNA analysis in the diagnostic pathway of familial CCM and expand the knowledge of abnormal splicing patterning in this disorder.

Familial Cerebral Cavernous Malformation Syndrome with Concomitant Fourth Ventricular Ependymoma: True Association or Mere Coincidence?

Familial cerebral cavernous malformation syndromes are most commonly caused by mutations in one of three genes. The overlap of these genetic malformations with other acquired neoplastic lesions and congenital malformations is still under investigation. To the best of our knowledge, the concurrent occurrence of familial cavernous malformations and ependymoma has not been previously reported in the literature. Herein, we describe a patient with familial cerebral cavernous malformation syndrome and posterior fossa ependymoma. A 17-year-old asymptomatic male was referred to our outpatient neurosurgery clinic after genetic testing identified a familial KRIT1 (CCM1) mutation. The patient's sister had presented with a seizure disorder previously; multiple cavernous malformations were discovered, and a symptomatic large cavernous malformation required a craniotomy for resection. Two years later, she was diagnosed with follicular thyroid cancer due to HRAS (c.182A>G) mutation. The patient and his sister were found to have a novel germline KRIT1 disease-causing variant (c.1739deletion, p.ASN580Ilefs*2) and a variant of uncertain significance, potentially pathogenic (c.1988 A>G, p.Asn663Ser) in cis in CCM1 (KRIT1), of paternal inheritance. Due to the presence of genetic abnormalities, the patient underwent screening imaging of his neuraxis. Multiple cavernous malformations were identified, as was an incidental fourth ventricular mass. Resection of the fourth ventricular lesion was performed, and histopathological examination was consistent with ependymoma. We report a unique case of posterior fossa ependymoma in an individual with a familial cerebral cavernous malformation syndrome and a novel genetic abnormality in KRIT1. The association of these two findings may be valuable in determining a potential genetic association between the two pathologies and elucidating the pathogenesis of both cavernous malformations and ependymomas.

Genetic and molecular basis of epilepsy-related cognitive dysfunction

Epilepsy is a common neurological disease characterized by recurrent seizures. About 70 million people were affected by epilepsy or epileptic seizures. Epilepsy is a complicated complex or symptomatic syndromes induced by structural, functional, and genetic causes. Meanwhile, several comorbidities are accompanied by epileptic seizures. Cognitive dysfunction is a long-standing complication associated with epileptic seizures, which severely impairs quality of life. Although the definitive pathogenic mechanisms underlying epilepsy-related cognitive dysfunction remain unclear, accumulating evidence indicates that multiple risk factors are probably involved in the development and progression of cognitive dysfunction in patients with epilepsy. These factors include the underlying etiology, recurrent seizures or status epilepticus, structural damage that induced secondary epilepsy, genetic variants, and molecular alterations. In this review, we summarize several theories that may explain the genetic and molecular basis of epilepsy-related cognitive dysfunction.

Alternatively spliced isoforms reveal a novel type of PTB domain in CCM2 protein

Cerebral cavernous malformations (CCMs) is a microvascular disorder in the central nervous system. Despite tremendous efforts, the causal genetic mutation in some CCM patients has not be identified, raising the possibility of an unknown CCM locus. The CCM2/MGC4607 gene has been identified as one of three known genes causing CCMs. In this report, we defined a total of 29 novel exons and 4 novel promoters in CCM2 genomic structure and subsequently identified a total of 50 new alternative spliced isoforms of CCM2 which eventually generated 22 novel protein isoforms. Genetic analysis of CCM2 isoforms revealed that the CCM2 isoforms can be classified into two groups based on their alternative promoters and alternative start codon exons. Our data demonstrated that CCM2 isoforms not only are specific in their subcellular compartmentation but also have distinct cellular expression patterns among various tissues and cells, indicating the pleiotropic cellular roles of CCM2 through their multiple isoforms. In fact, the complexity of the CCM2 genomic structure was reflected by the multiple layers of regulation of CCM2 expression patterns. At the transcriptional level, it is accomplished by alternative promoters, alternative splicing, and multiple transcriptional start sites and termination sites; while at the translational level, it is carried out with various cellular functions with a distinguishable CCM2 protein group pattern, specified abundance and composition of selective isoforms in a cell and tissue specific fashion. Through experimentation, we discovered a unique phosphotyrosine binding (PTB) domain, namely atypical phosphotyrosine binding (aPTB) domain. Some long CCM2 isoform proteins contain both classes of PTB domains, making them a dual PTB domain-containing protein. Both CCM1 and CCM3 can bind competitively to this aPTB domain, indicating CCM2 as the cornerstone for CCM signaling complex (CSC).

CCM1 and CCM2 variants in patients with cerebral cavernous malformation in an ethnically Chinese population in Taiwan

Cerebral cavernous malformation (CCM) is a vascular malformation characterized by clustered enlarged capillary-like channels in the central nervous system. The genes harboring variants in patients with CCM include CCM1/Krev interaction trapped-1, CCM2/MGC4607, and CCM3/programmed cell death protein 10. We aimed to identify pathogenic variants in an ethnic Chinese population in Taiwan. We recruited 95 patients with multiple CCMs or a single lesion with a relevant family history. Sanger sequencing was performed for 41 patients. Variants were identified using sequence alignment tools, and the clinical significance of these variants was determined using American College of Medical Genetics and Genomics standards and guidelines. Several pathogenic variants were found in six patients, including three unrelated patients and three affected members of one family. Two novel pathogenic variants leading to early truncation comprised a deletion variant in exon 18 of CCM1 (c.1846delA; p.Glu617LysfsTer44) and an insertion variant in exon 4 of CCM2 (c.401_402insGCCC; p.Ile136AlafsTer4). One novel pathogenic splice site variant was c.485 + 1G > C at the beginning of intron 8 of CCM1. In this study, we identified novel variants related to CCM in an ethnically Chinese population in Taiwan.

Novel KRIT1/CCM1 and MGC4607/CCM2 Gene Variants in Chinese Families With Cerebral Cavernous Malformations

Familial cerebral cavernous malformations (CCMs) are autosomal dominant disorders characterized by hemorrhagic strokes, recurrent headache, epilepsy, and focal neurological deficits. Genetic variants in KRIT1/CCM1, MGC4607/CCM2, and PDCD10/CCM3 genes contribute to CCMs. The clinical information of two Chinese families with CCMs was collected. MRI and video-electroencephalography were performed. Genetic variants of CCM1, CCM2, and CCM3 genes were investigated by exome sequencing. The patients were presented with recurrent epilepsy or headache. Susceptibility-weighted images of brains showed many dark dots, while video-electroencephalography revealed many spikes from multiple brain regions of patients. Exome sequencing revealed a novel CCM1 genetic variant (c.1599_1601TGAdel, p.Asp533del) and a novel CCM2 genetic variant (c.773delA, p.K258fsX34) in Family one and Family two, respectively; cosegregation existed in these two families. The two family members presented typical CCMs symptoms. These two novel genetic variants in CCM1 and CCM2 genes were the causation of CCM in the two Chinese families, and our data enriched the genetic variant spectrum of CCM genes.

A Novel CCM1/KRIT1 Heterozygous Nonsense Mutation (c.1864C>T) Associated with Familial Cerebral Cavernous Malformation: a Genetic Insight from an 8-Year Continuous Observational Study

Cerebral cavernous malformation (CCM) is a congenital vascular abnormality that predominantly affects the central nervous system, but that sometimes encroaches other vital tissues, including the retina, skin, and even liver. The familial form of CCM (FCCM) is considered to be an autosomal dominant disease with incomplete penetrance and variable expression, which is often attributed to mutations in three genes: CCM1, CCM2, and CCM3. We screened a Chinese family diagnosed with FCCM by using Sanger sequencing. A 29-year-old male proband with cutaneous angiomas was pathologically diagnosed but presented with an atypical form of CCM as revealed by magnetic resonance imaging (MRI) findings, prompting further clinical evaluation and genetic analyses of him and his immediate family. We performed continuous observation over an 8-year period using MRI gradient echo imaging and susceptibility-weighted imaging of these individuals. Sanger sequencing of the CCM1, CCM2, and CCM3 genes identified a novel heterozygous nonsense nucleotide transition (c.1864C>T; p.Gln622X) in exon 17 of the CCM1/KRIT1 gene; this mutation was predicted to cause a premature stop codon (TAG) at nucleotides 1864 to 1866 to generate a truncated Krev interaction trapped 1 (Krit1) protein of 621 amino acids. During this long-term observational study, one of the enrolled family members with neurological deficits progressed to a stage indicative of brain surgery. This study provides a new CCM gene mutation profile, which highlights the significance of genetic counseling for individuals suspected of having this condition.

A Novel KRIT1/CCM1 Gene Insertion Mutation Associated with Cerebral Cavernous Malformations in a Chinese Family

Familial cerebral cavernous malformation (FCCM) is a vascular malformation disorder that closely associated with three identified genes: KRIT1/CCM1, MGC4607/CCM2, and PDCD10/CCM3. Here, we present a Chinese family affected by FCCM due to a novel KRIT1/CCM1 insertion mutation. The proband was hospitalized for sudden unconsciousness and underwent surgical treatment. The section of lesions showed classical cavernous-dilated vessels without intervening brain parenchyma, and hemosiderin-laden macrophages were accumulated in the surrounding tissue. In addition, magnetic resonance imaging (MRI) showed severe multiple cerebral cavernous malformation (CCM) lesions in cerebrum, brainstem, and cerebellum in other affected subjects. Especially, for the proband's mother, hundreds of lesions were presented, and a few lesions were found in the expanded lateral ventricle (Evans' index =0.33). Moreover, she showed the similar symptoms of hydrocephalus, including headache, dizziness, and diplopia. It was extremely rare in previous reports. To date, the genetic alterations leading to FCCM in Chinese population remain largely unknown. We investigated genetic defects of this family. Sequence analyses disclosed a novel heterozygous insertion mutation (c.1896_1897insT; p.Pro633SerfsTer22) in KRIT1/CCM1. Moreover, our real-time PCR results revealed that the mRNA level of KRIT1/CCM1 were significantly decreased in FCCM subjects (CCM family =0.42 ± 0.20 vs. healthy control =1.01 ± 0.16, P = 0.004). It indicated that this mutation could cause KRIT1/CCM1 functional mRNA deficiency. It may be closely related with the pathogenesis of FCCM. Our findings provided a new gene mutation profile which will be of great significance in early diagnosis and appropriate clinical surveillance of FCCM patients.