Along with midline defects such as cleft lip and/or palate, cyclopia, and proboscis, a baby with trisomy 13 may have holoprosencephaly, a condition in which the brain does not form into two complete cerebral hemispheres. Seen here is the "alobar" form of holoprosencephaly in which there is only a single large ventricle. [Image contributed by Jeannette J. Townsend, MD, University of Utah]

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