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

Abstract

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.

Figure 1

Pedigree of three affected patients with one pathogenic CCM1 variant from one family. A square represents a male patient, whereas a circle represents a female patient. A line across the symbol indicates the patient is deceased.

Figure 2

Brain MRI of patients with CCM variants. (A) Patient 20 with two CCM1 variants: multiple lesions of variable sizes in hemispheres in susceptibility weighted imaging (SWI); (B) Patient 20 with one spinal cord lesion in a T2-weight image; (C) Patient 40 with one CCM1 variant: multiple small lesions in hemispheres in SWI; (D–F) Patients 57 (D), 66 (E), and 67 (F) from one family with one CCM1 variant: multiple hemisphere lesions with variable sizes in SWI; (G,H) Patient 54 with one CCM2 variant: one prominent pontine lesion (G) and small lesions in bilateral hemispheres (H) in SWI; (I) Patient 69 with one CCM2 variant of uncertain significance: one lesion in the right pons and the other in the right basal ganglion (not shown) (arrow indicates the lesion).

Figure 3

Five sequencing chromatograms of patients with variants. Each part includes a chromatogram, an interpreted sequence, reference sequences (human), and an amino acid sequence (left side). The area of intron is marked within a rectangle with a dotted line, and the sites of variants are marked within the rectangle with a solid line. The underlying lines below the sequence indicate reading frames. (A) CCM1 in Patient 20: one missense (G > C) and one deletion (del-A) variant within exon 18, leading to frameshift. (B) CCM1 in Patient 40: one splice site variant (G > C) at the first base pair of intron 8. (C) CCM1 in Patients 57, 66, and 67: one 3-base pair deletion (del-GTA) variant in intron 13, alternating mRNA splicing. (D) CCM2 in Patient 54: one 4-base pair insertion variant (ins-GCCC) within exon 4, causing frameshift. (E) CCM2 in Patient 69: one missense variant (G > A) within exon 9.

Figure 4

Schematic representation of the gene structure and protein domains of (A) CCM1 (KRIT1) and (B) CCM2 in a Chinese population. Each part contained an upper panel and a lower panel. The upper panel contains the genetic structure and exon position and number, and the lower panel contains a corresponding protein product and its specific domain. Each variant is marked with a double-headed arrow, indicating a variant and corresponding amino acid change, respectively. All variants reported previously in the Chinese population are shown, and variants reported in these studies are marked with rectangles.