chromosome 4, deletion of short arm
a chromosomal disorder involving absence of a portion of chromosome 4, resulting in microcephaly, delayed growth, visual defects, intellectual disability, and seizures. The size of the deleted genetic material varies, and studies suggest that larger deletions tend to result in more severe intellectual disability and physical abnormalities than do smaller deletions. Although sometimes the disorder is passed on from an unaffected parent, most cases are not inherited. Also called Wolf–Hirschhorn syndrome.