Anatomical observations of holoprosencephaly in swine

In a study of swine congenital anomalies, nine newborn piglets with varying degrees of optic hypotelorism including cyclopia were collected. Nasal and maxillary development were abnormal in all animals regardless of the degree of eye fusion. All animals except one had intact upper lips and hard palates that carried two or three small extopic teeth. The "snout" was only a medial wedge-shaped rudiment projecting from the upper lip. It was distally covered by a typical snout-like glabrous epithelium and carried small vibrissae. Six animals also had a tubular proboscis dorsal to the eye. The distal tip of the proboscis was covered by glabrous epithelium. External nares and nasal passageways, albeit blind-ended, were prominent in the proboscis. The nasofrontal bones projected into the base of the proboscis. Seven piglets were hairless except for fine vibrissae and some eyebrow hairs. All animals had some degree of ear abnormalities, e.g., malposition and absence of external auditory meatus. In all animals the brain was malformed. This abnormality varied from complete absence of the forebrain to an alobar structure with gyri. The remainder of the body of each animal was normal. Developmental anomalies of the nose and eye generally reflect malformations of the forebrain, although the etiology of these defects is unclear. The cyclopia associated with the medial proboscis suggests that both the telencephalon and diencephalon are dysplastic. The presence of glabrous epithelium in two regions on the face suggests that studies of the development of the midline face in the swine will help to elucidate the etiology of the holoprosencephalic series. In this way the pig may prove to be an excellent modeling system for human holoprosencephaly.