Laboratory mice, for example, have become a powerful tool for the study of human disease. They are expected to prove particularly useful for dissecting the interactions involved in complex genetic traits, where gene action is modified by the behavior of additional genes, and often by environmental factors as well. Such a mouse model system is helping to shed light on human Hirschsprung disease, a congenital impairment of intestinal function in which part of the colon lacks nerve cells and so is unable to relax. The result in chronic constipation and distention of the abdomen. The disorder, which affects about 1 in 5000 U.S. newborns, is usually diagnosed in infancy.
Treatment involves surgical removal of the affected portion of the colon.
One form of human Hirschsprung disease appears to be due to an autosomal dominant gene on chromosome 10. But it probably accounts for fewer than one in five cases of the disorder, so the search continues for additional candidate genes. The gene's product is not yet know, but is effects appear to depend on the presence of modifier genes. Researchers suspect that the human homolog of ls lies on chromosome 20, and may be responsible for at least some cases of Hirschsprung disease. In collaboration with scientists at Philadelphia's Thomas Jefferson University and Mississippi State University, the scientists have zeroed in one the mouse mutation's likely chromosomal location.