Alobar Holoprosencephaly in an Aborted American Quarter Horse Fetus.

This research focuses on a case of Holoprosencephaly, a brain malformation, in a fetus of an American Quarter Horse that was aborted at 9 months. Despite analyzing the genetic makeup of the fetus, no gene mutations associated with this disease in humans were found.

About Holoprosencephaly

• Holoprosencephaly is a malformation in the central nervous system. It often involves incomplete or total absence of the division of prosencephalon hemispheres, a portion of the brain.
• This condition is often accompanied by malformations in the facial structure.

Case Study: The Quarter Horse Fetus

• A 9-month gestation Quarter Horse fetus was studied following an abortion. The fetus showed multiple severe abnormalities.
• These included lack of haircoat, marked shortening or absence of several facial bones including the maxillary, incisive, and nasal bones, and bilateral anophthalmia, a condition where one or both eyes are absent.
• The brain was notably small and almost perfectly round, composed of just one lobe with no discernible separation between cerebral hemispheres.
• Important structures in the brain like the olfactory bulbs, piriform lobes, and optic chiasm were completely absent.
• On further analysis, the researchers discovered that the brain’s inner structures were replaced by a monoventricle lined by the remaining compressed cortex. The two thalami, usually separated in a normal brain, were fused in this case.

Genetic Analysis

• As mutations in the Sonic Hedgehog (SHH) gene are associated with human cases of holoprosencephaly, the researchers sequenced the three coding SHH exons present in the liver DNA of the fetus.
• However, they found that the SHH sequence in the horse was similar to the Equus caballus (horse) SHH mRNA sequence already documented in the Genbank gene database.
• As a result, they found no evidence of a polymorphism, or genetic variation, in the coding region of this gene that could explain the observed phenotype, or physical traits.

Conclusion

• This is reportedly the first documented instance of alobar holoprosencephaly, a severe form of holoprosencephaly, in horses.
• Despite thorough genetic analysis, no gene mutations associated with this disease in humans were identified in this case.