Restriction of arterial blood supply to the brain associated with insufficient oxygenation to support the metabolic requirements of the tissue.

A loss of global cognitive ability of sufficient amount to interfere with normal social or occupational function. Dementia represents a loss of previously present cognitive abilities, generally in adults, and can affect memory, thinking, language, judgment, and behavior.

Homozygous loss-of-function mutations in the HOXA1 gene result in disorders with variable phenotypic expressivity that span a spectrum. Two related, but somewhat distinctive, phenotypes have been described in different populations: the Athabaskan brainstem dysgenesis syndrome (ABDS) in Native Americans, and Bosley-Salih-Alorainy syndrome (BSAS) in individuals from the Middle East, including Turkey and Saudi Arabia. Features common to both disorders include Duane retraction syndrome with variable gaze palsies, sensorineural deafness associated with inner ear abnormalities, and delayed motor development. More variable features, observed in both disorders, include conotruncal cardiac malformations, cerebral vascular malformations, and impaired intellectual development with autism. Unique to ABDS are central hypoventilation, often resulting in early death, facial weakness, and more severe cognitive deficits. These features are thought to be due to a more severe malformation of the hindbrain in ABDS compared to BSAS (summary by Tischfield et al., 2005).