Frontonasal dysplasia (also known as the Burmese head defect) is a hereditary disease in Burmese cats caused by a mutation in the ALX1 gene. Cats with two copies of the variant (homozygous) are born with severe craniofacial defects, including missing midline facial structures, duplicated teeth and whisker fields, brain protrusion (meningoencephalocele), and eye degeneration; affected kittens cannot survive and require euthanasia. Cats with one copy (heterozygous) show a brachycephalic head type.
