A Novel CCM2 Missense Variant Caused Cerebral Cavernous Malformations in a Chinese Family

Abstract

Cerebral cavernous malformations (CCMs) are common vascular malformations in the central nervous system. Familial CCMs (FCCMs) are autosomal dominant inherited disease with incomplete penetrance and variable symptoms. Mutations in the KRIT1, CCM2, and PDCD10 genes cause the development of FCCM. Approximately 476 mutations of three CCM-related genes have been reported, most of which were case reports, and lack of data in stable inheritance. In addition, only a small number of causative missense mutations had been identified in patients. Here, we reported that 8/20 members of a Chinese family were diagnosed with CCMs. By direct DNA sequencing, we found a novel variant c.331G > C (p.A111P) in exon 4 of the CCM2 gene, which was a heterozygous exonic variant, in 7/20 family members. We consider this variant to be causative of disease due to a weaken the protein-protein interaction between KRIT1 and CCM2. In addition, we also found the exon 13 deletion in KRIT1 coexisting with the CCM2 mutation in patient IV-2, and this was inherited from her father (patient III-1H). This study of a Chinese family with a large number of patients with CCMs and stable inheritance of a CCM2 mutation contributes to better understanding the spectrum of gene mutations in CCMs.

Keywords: CCM2; chinese family; familial cerebral cavernous malformation; missense variant; susceptibility-weighted imaging.

FIGURE 1

Radiological and histopathological information of patient II-1. CT (A,B) and GRE T2-weighted MRI (C,D) showed multiple cavernous malformation lesions across the left lateral ventricle and bilateral cerebral hemisphere in the proband, patient II-1. The red arrows show the location of lesions. Histopathological examination revealed vascular malformation associated with bleeding (→), calcification (↑), and iron deposits (←) in the proband, patient II-1, at (E) ×100, and (F) ×100.

FIGURE 2

Pedigree of a Chinese family. Affected patients were diagnosed with CCMs upon T2-weighted MRI or SWI of the brain.

FIGURE 3

CCM lesions diagnosed through CT, T2-weighted MRI and SWI. (A–C) SWI of patient I-2 showed hundreds of lesions distributed across the cerebral hemisphere and cerebellum. T2-weighted MRI of patient II-4 showed multiple CCMs in the right temporal lobe (D), frontal and parietal lobes (E), and spinal cord (F,G). CT (H), T2-weighted (I), and contrast MRI (J) of patient II-5 showed lesions with a “popcorn” appearance located in the right lateral ventricle and frontal-parietal lobe with asymmetrical ventricles. (K,L) T2-weighted MRI of patient III-1 showed lesions surrounded by a dark rim of hemosiderin on the right frontal and temporal lobes. (M) T2-weighted MRI of patient III-2 showed a lesion located on the left temporal lobe. (N,O) T2-weighted MRI of patient IV-1 showed lesions on the left temporal lobe and triangle area of the lateral ventricle. (P) T2-weighted MRI of patient IV-2 showed a lesion located in the left triangle area of the lateral ventricle. The red arrows show the CCM lesions.

FIGURE 4

Location of the novel missense mutation. (A) Schematic representation of the genetic structure and protein domains of CCM2. The novel missense mutation c.331G > C (p.A111P) is located in the PTB domain of exon 4 in the CCM2 gene. (B) A novel heterozygous missense mutation was detected by Sanger sequencing. (Upper panel) The normal sequences of the CCM2 gene. (Lower panel) The genetic variant of c.331G > C chr7-45104104 (p.A111P). The affected nucleotide is indicated with red arrows. (C) Comparison of the DNA-related content in exon 13 in KRIT1. Data among the standard, patient IV-2, and patient III-1H (father of patient IV-2) were shown.

FIGURE 5

Three-dimensional structure of the PTB domain generated by PyMOL software. The panel shows the overlap between the wild-type (A) and mutated (B) tertiary protein structures. p.A111P: superimposed structures of the malcavernin protein with the native Ala111 residue and Pro111 residue substitution. The yellow arrow indicates the region where the A111P substitution resides, and the dotted red lines indicate the alteration in the intramolecular H bonds in the area of the substitution.