congenital absence of parasympathetic ganglion cells.
congenital defect manifested by stenosis, but patency, of the colon, an absence of ganglia of the myenteric plexus and an almost complete absence of skin pigment in white foals resulting from matings between overo horses. The foal develops colic at birth and dies after about 48 hours. See also atresia. Occurs also in some spotted mutant strains of mice. Called also congenital megacolon, aganglionic megacolon.