Subcortical ischemic
vascular dementia (SIVD) is a main subgroup of
vascular dementia related to
cerebral small vessel disease. Risk factors for SIVD include
hypertension, ageing, and
diabetes mellitus, but the specific contribution of each factor to the development of
cerebral small vessel disease remains obscure. This is mainly because SIVD in the elderly might be affected by many factors related to the ageing process. Hereditary
cerebral small vessel diseases, including cerebral autosomal-dominant or autosomal recessive arteriopathy with subcortical
infarcts and
leukoencephalopathy (
CADASIL or
CARASIL) and
cerebral amyloid angiopathy, are affected by different pathomechanisms, but these diseases indicate a clear a role of the cerebral small vessel on subcortical
dementia.
CADASIL is caused by a
cysteine residue-related mutation in the
EGF-like repeat on the extracellular domain of Notch3. Pathological examination of a
CADASIL brain indicated abnormal accumulation of the extracellular domain of Notch3 with
extracellular matrix proteins, including
tissue inhibitor of metalloproteinase 3 and
vitronectin, around vascular smooth muscle cells.
CARASIL is caused by a mutation in HTAR1, a
serine protease that regulates
transforming growth factor (
TGF)-beta signaling. The mutation in HTAR1 related to
CARASIL fails to repress
TGF-beta signaling and induces the accumulation of extracellular matrix, including the extra domain-A region of
fibronectin and
versican. The individual and common pathomechanisms of hereditary
cerebral small vessel disease are discussed in this review.