CADASIL and CARASIL

Abstract

CADASIL and CARASIL are hereditary small vessel diseases leading to vascular dementia. CADASIL commonly begins with migraine followed by minor strokes in mid-adulthood. Dominantly inherited CADASIL is caused by mutations (n > 230) in NOTCH3 gene, which encodes Notch3 receptor expressed in vascular smooth muscle cells (VSMC). Notch3 extracellular domain (N3ECD) accumulates in arterial walls followed by VSMC degeneration and subsequent fibrosis and stenosis of arterioles, predominantly in cerebral white matter, where characteristic ischemic MRI changes and lacunar infarcts emerge. The likely pathogenesis of CADASIL is toxic gain of function related to mutation-induced unpaired cysteine in N3ECD. Definite diagnosis is made by molecular genetics but is also possible by electron microscopic demonstration of pathognomonic granular osmiophilic material at VSMCs or by positive immunohistochemistry for N3ECD in dermal arteries. In rare, recessively inherited CARASIL the clinical picture and white matter changes are similar as in CADASIL, but cognitive decline begins earlier. In addition, gait disturbance, low back pain and alopecia are characteristic features. CARASIL is caused by mutations (presently n = 10) in high-temperature requirement. A serine peptidase 1 (HTRA1) gene, which result in reduced function of HTRA1 as repressor of transforming growth factor-β (TGF β) -signaling. Cerebral arteries show loss of VSMCs and marked hyalinosis, but not stenosis.

Keywords: CADASIL; CARASIL.

Figure 1

A schematic presentation of Notch signaling. Notch3 is constitutively cleaved by furin (S1) and the bipartite molecule is inserted to the plasma membrane (PM). The extracellular domain (N3ECD) consists of 34 epidermal growth factor (EGF)‐like repeats, followed by three notch/lin‐12 repeats, a transmembrane domain and an intracellular domain (NICD), which contains seven ankyrin repeats. The binding site of the ligand (in human Delta or Jagged) is at EGF repeats 10–11. Upon binding, N3ECD is cleaved external to the intramembranous domain (S2). Thereafter occurs the intramembranous S3 cleavage and NICD enters the nucleus to release the repressor molecules CoR and HDAc, and it binds to a transcription regulator of CSL family, RBP‐Jκ, and activates transcription. CADASIL mutations are in EGF repeats 1–32 (exons 2–23) between the asterisks. EC = extracellular space, IC = intracellular space, NM = nuclear membrane, N = nucleus, TACE = tumor necrosis factor α‐converting enzyme, HD = heterodimerization domain, CoR and HDAc = repressors, HAc and MAML1 = components of an activation complex.

Figure 2

A schematic presentation of HTRA 1 mutations. The mutations reported in Far‐Eastern patients are presented below the gene and those in Caucasian patients are presented above the gene. Missense mutations are presented in black, nonsense mutations in red and the compound heterozygous mutation in green. [Domains of HTRA1. Red: Insulin‐like growth factor binding protein domain. Green: Kazai‐type serine protease inhibitor domain. Blue: Trypsin‐like serine protease domain. Yellow: PDZ domain. Scheme modified after Hara et al 45; for details see Table 1].

Figure 3

Loss of hair is clearly noticeable already at the age of 34 years in this male CARASIL patient (A). At the age of 33 years, T2‐weighted MRI disclosed diffuse leukoencephalopathy and lacunes (B and C).

Figure 4

Three old infarcts of moderate size in cerebral white matter (open arrows) and smaller lacunar infarcts in putamen bilaterally (arrows) in a 65‐year‐old female CADASIL patient with p.Arg133Cys Notch3 mutation. Note the relatively spared cortex except for the ischemic lesion in temporal cortex (arrowhead) because of atherosclerotic occlusion of a middle cerebral artery branch [black triangle; (A)]. In this same patient's caudate nucleus, the lesions are more severe than in putamen. In the WM of the centrum semiovale, there is another small cystic infarct [open arrow; (B)]. Lateral ventricles in both (A) and (B) are widened because of ischemic tissue loss.

Figure 5

Compared with a control person's cerebral WM arteriole (A), the wall of a CADASIL patient's arteriole (B) is markedly thickened and fibrotic, and its rigidity renders the arteriole exceptionally circular (C). Tunica media is slightly basophilic in hematoxylin and eosin (H&E) (B) and prominently positive in periodic acid Schiff (PAS) staining (C). In advanced disease, the fibrosis has almost completely obliterated the lumen (D). Similarly, as in dermal arteries, NOTCH3 extracellular domain (N3ECD) immunopositivity accumulates in the tunica media of the thickened WM arterioles (E). The irregularly decreased immunoreactivity for α‐smooth muscle actin (α‐SMA) in the wall of a WM arteriole reflects the degeneration of VSMCs (G). The thickened adventitia harbors extracellular matrix proteins, here shown by collagen type I immunohistochemistry (F). vG = van Gieson.

Figure 6

The lumina of a WM (A) and a cortical (B) arteriole are approximately as wide and approximately similar amount of N3ECD is deposited in their tunica media, but the wall of the WM arteriole is almost fourfold thicker than that of the cortical arteriole because of the marked fibrosis. N3ECD is also deposited in the wall of a probable vein beside the arteriole (B). Delicate N3ECD immunopositivity is already present in the wall of a markedly thickened arteriole in the cerebral WM of an only 32‐year‐old male CADASIL patient (C). In an elderly patient, N3ECD immunopositivity is seen on capillaries in both cerebral WM (D) and cortex (E), as well as in the walls of larger leptomeningeal arteries (F).

Figure 7

An electron micrograph (EM) of a small dermal artery from a 28‐year‐old male CADASIL patient with p.Arg133Cys NOTCH3 mutation. Three small deposits of GOM (arrows) are detectable (already at this age) on a few vascular smooth muscle cells (VSMC). The subendothelial space is widened with accumulation of extracellular matrix proteins (asterisks). E = endothelium, N = nucleus (A). An EM of a dermal arteriole from a 19‐year‐old CADASIL patient [younger brother of the patient in (A), both sons of a male patient homozygous for p.Arg133Cys mutation] shows the paucity of GOMs (arrowhead) and the inset shows that true GOMs do occur already at this young age (B). A higher magnification EM of a dermal arteriole from an elderly patient at a more advanced stage of the disease. GOMs are present both in indentations on a VSMC (black asterisks) and in the intercellular space apparently disconnected to the VSMC (white asterisk) (C). Note the pinocytotic vesicles in the VSMC beneath the GOM (B and C insets). N = nucleus. [Fig. 7A is reproduced from article (62) with permission]

Figure 8

Immunohistochemical visualization of N3ECD deposition in the walls of dermal arteries (asterisks). The granular immunoreactivity is visualized either by using immunoperoxidase method (A) or—at a higher resolution—using confocal immunofluorescence, the punctate pattern being consistent with scattered distribution of GOMs (B). N = nerve.

Figure 9

The cerebral white matter of a CARASIL patient who died at the age of 54 years shows diffuse widespread loss of myelin with preservation of U‐fibers (A). A small artery from a cerebral white matter shows irregular structure with double barreling of the thickened wall. Internal elastic lamina is multiplied (B). The wall of a medium‐sized leptomeningeal artery is markedly thickened with replacement of tunica muscularis by fibrous tissue, intimal proliferation and splitting of the internal elastic lamina. The smaller arteries beside show loose double barreling (C).

Figure 10

Occasionally microbleeds (arrows) in cerebral cortex may be visible already during brain cutting (A). An accumulation of hemosiderin around a cortical arteriole stains strongly positively for iron (B). The breached BBB at the microbleed leaks plasma fibrinogen (brown; C). The wall of a cortical arteriole (D) is markedly thinner than that of a WM arteriole (E; blue bars in D vs. E), while their outer diameters (red bars) are of approximately the same magnitude. This is a likely explanation for the predominant location of microbleeds in cortical and deep GM. The thick wall of a WM arteriole from a CADASIL patient at a quiescent stage of the disease has not allowed virtually any leakage of fibrinogen (E). Extravasated fibrinogen is normally taken up by Purkinje cells (PCs) from cerebrospinal fluid 51. Thus, negative fibrinogen staining of cerebellar PCs (arrows; F) verifies that significant leakage has not occurred in this patient at a quiescent stage, whereas in another CADASIL patient, who had suffered an infarct just before death, PCs (arrows) are strongly immunopositive for fibrinogen reflecting the breakdown of BBB (G).

Figure 11

(A) Representative electron micrographs of the corpus callosum from a TgPAC‐Notch3^{R 169 C} showing multiple membrane‐bound vacuoles (colored in pink) including numerous inframicrometric vacuoles (white arrows). O = oligodendrocytes (colored in green); A = astrocyte (colored in purple); C = capillary (colored in yellow). (B) Typical large vacuole (asterisk) in the innermost layer of the myelin sheath. The vacuole separates the axon from its myelin sheath (black arrowheads) and contains multiple aberrant myelin sheets (arrows). Notice the thin myelin sheet (open arrowhead) at the interface between the axon and the vacuole. Scale bar represents 5 μm in (A) and 1 μm in (B).