ABSTRACT
In the 28-week female fetus with Trisomy 18 and cyclopia we dissected, there was a single orbit with no metopic suture and no proboscis. The complete absence of a proboscis was peculiar, since most reported cases of cyclopia feature some structure above the eye resembling a nasal region. McGrath (1992) states “in cyclopia the face is as normal as the absence of median structures permits.” The presence of a proboscis above the cyclopic eye is often assumed to be due to epigenetic factors, i.e., the nose cannot descend to its normal position because of the medial position of the eye. McGrath outlined the morphogenesis of the proboscis and how facial development is affected by the absence of median structures, but the complete absence of a proboscis in our case study may support a different model involving some other genetic or epigenetic perturbation, explaining why not all cyclopic cases result in the same morphology. This interpretation is consistent with Shapiro’s theory of homeostasis, or random phenotypic effects (see Chapter 1 and below).
