Mice homozygous for the congenital hydrocephalus (Foxc1ch) spontaneous mutation die at birth, probably from inability to breathe. Homozygous mutant mice have bulging hemorrhagic cerebral hemispheres and open eyelids, urogenital abnormalities, and severely abnormal skull, cervical vertebrae, sternum, laryngeal cartilages, and hyoid bone. The hydrocephalus may trace to lack of formation of subarachnoid space, which is first detectable in 11-day embryos. Most of the defects in the head region are probably secondary to the severe displacements created by the hydrocephalus. Mice homozygous for the muted spontaneous mutation (Bloc1s5mu), maintained in repulsion with congenital hydrocephalus, have light eyes at birth and their fur is a muted brown shade, often with white underfur. Some have a balance defect, similar to that of pallid (Bloc1s6pa). Homozygous mutant mice show head-tilting and loss of postural reflexes, due to absence of otoliths from the sacculus and utriculus of one or both ears. The bony labyrinth is normal; the mice are not deaf and do not circle. Mutant mice have prolonged bleeding times and a platelet storage pool deficiency (SPD) associated with abnormalities of the dense granules of the blood platelets.
