Although no specific genetic factor has yet been identified, multiple factors are believed to play a role in the expression of autism, given the variability in symptoms seen in children. Evidence for a genetic link is that AS tends to run in families where more family members have limited behavioral symptoms similar to AS (for example, some problems with social interaction, or with language and reading skills). Most behavioral genetic research suggests that all autism spectrum disorders have shared genetic mechanisms, but AS may have a stronger genetic component than autism. There may be shared genes in which particular alleles make an individual vulnerable, and varying combinations result in differing severity and symptoms in each person with AS.A few ASD cases have been linked to exposure to teratogens (agents that cause birth defects) during the first eight weeks from conception. Although this does not exclude the possibility that ASD can be initiated or affected later, it is strong evidence that ASD arises very early in development. Many environmental factors have been hypothesized to act after birth, but none has been confirmed by scientific investigation.
Occasionally, atheroma in the parent artery blocks the orifice of the penetrating artery (luminal atheroma), or atheroma involves the origin of the penetrating artery (junctional atheroma). Alternatively, hypoperfusion is believed to be the mechanism when there is stenosis of the penetrating artery. When no evidence of small vessel disease is found on histologic examination, an embolic cause is assumed, either artery-to-artery embolism or cardioembolism. In one recent series, 25% of patients with clinical radiologically defined lacunes had a potential cardiac cause for their strokes. More recent advances have also suggested these mechanisms may play a combined role in the aetiology of lacunar infarction. The most current theory indicates endothelial dysfunction and increased permeability of the blood-brain barrier first allow leakage of blood contents, promoting gliosis and white matter hyper-intensities on magnetic resonance imaging. Moreover, focal narrowing of brain vessels and impairment of their ability to dilate in response to various stimuli may lead to a decreased cerebral blood flow and ultimately lacunar stroke.Advanced age, chronic hypertension, smoking and diabetes mellitus are risk factors. It is unclear whether there is an association with alcohol consumption, elevated cholesterol, or history of prior stroke. Lacunar strokes may result from carotid artery pathology or microemboli from the heart as in atrial fibrillation. Patients often recover well, but if there is enough white matter disease from lacunar pathology, one can see a subcortical dementia such as Binswanger disease.