DNAH11 is important for developmental control of organ positioning in the left-right axis such that homozygosity for the situs inversus viscerum (iv) mutant allele can result not only in inverse placement of the visceral and thoracic organs, but also in anomalous positioning and interactions of blood vessels (including the hepatic portal, inferior vena cava, and azygos vein) and modified shape of organs and blood vessels, including abnormal lobation of lungs or liver. Approximately 50% of mice homozygous for Dnah11iv have situs inversus, and the likelihood of situs inversus is not impacted by whether the homozygous parent has situs inversus. This indicates that wild type Dnah11 instructs left-right asymmetry, and in the absence of functional Dnah11 the direction of this asymmetry is random. Heterotaxia is found in less than half of homozygotes and occurs equally in those that do and do not have situs inversus. While heterotaxia may be impacted by genetic background, the incidence of situs inversus has not shown this variation. Situs inversus can be identified shortly after birth, until the skin thickens at approximately day 5, by viewing the location of the milk-filled stomach through the skin. Homozygotes are generally viable and do breed, although poorreproductive performance with a high rate of resorption has been reported by Brown et al. (Development 1989). Some premature death has been reported and may be caused by deformities of the cardiac loop. (Hummel and Chapman, 1959; Layton 1976; Brown et al., 1989; Icardo and Colvee, 2001.)
