Aprosencephaly with otocephaly in a lamb (Ovis aries).

Aprosencephaly is a rare condition in veterinary and human medicine characterized by the complete absence of telencephalon and diencephalon. Some cases are accompanied by a facial dysmorphism designated as otocephaly. A stillborn lamb had splanchnocranial anomalies that were classified by computed tomography, magnetic resonance imaging, and pathologic examination as aprosencephaly and otocephaly. The brain included parts of the cerebellum and brainstem but no telencephalon, diencephalon, or mesencephalon. The cerebellum had a structurally normal cortex with expression of neuronal nuclear antigen in the inner and doublecortin in the outer granular cell layers, as well as an irregularly situated nucleus dentatus. Aprosencephaly with otocephaly has been described in mice with heterozygous mutations in the Otx2 gene; however, no causative polymorphisms were detected in the Otx2 gene region of this lamb.