Some congenital defects (defects present at birth), are inherited from the parents, while others are caused by environmental factors in the womb, such as nutritional deficiencies or some viral infections. For many, the cause is unknown.
Kittens are born with a nervous system that is not fully developed, and birth defects may not become apparent until they begin to walk. In some cases, evidence of an inherited disorder may not be seen until the cat has reached adulthood, even though the defect has been present since birth.
Birth defects of the nervous system are categorized according to the primary region of the nervous system affected: forebrain, cerebellum, spinal cord, peripheral nerve and muscle disorders, or multifocal disorders that include signs of more than one area. Many of these inherited disorders are rare or breed-specific, or both. A few of the more common disorders of each area are described below.
Hydranencephaly has been described mainly in kittens who were exposed to feline panleukopenia virus/parvovirus (see Disorders Affecting Multiple Body Systems of Cats: Feline Panleukopenia) while in the womb. This can also cause brain stem malformations and cerebellar hypoplasia.
In cerebellar hypoplasia, the cerebellum does not develop completely. This is caused by exposure of the kitten to feline panleukopenia virus/parvovirus (see Disorders Affecting Multiple Body Systems of Cats: Feline Panleukopenia) while in the womb. The kitten typically has a tremor that does not worsen as the cat matures, and affected animals can be good pets. Hydrocephalus can also be found in animals with cerebellar disorders.
Spinal Cord Disorders
Spina bifida occulta is a condition seen in Manx cats as a result of the spinal changes resulting in the tailless body type.
Peripheral Nerve and Muscle Disorders
Neuropathy of hereditary hyperchylomicronemia (hyperlipidemia) is an inherited disorder that causes peripheral nerve damage in cats. Signs do not develop until the kitten is at least 8 months of age. This condition causes granules of fat to be deposited within nerves, and some studies show that the signs can be controlled by a low-fat diet. Congenital megaesophagus is an enlarged esophagus that is inherited in Siamese cats. Signs include frequent vomiting and pneumonia.
Last full review/revision July 2011 by William B. Thomas, DVM, MS, DACVIM (Neurology); Kyle G. Braund, BVSc, MVSc, PhD, FRCVS, DACVIM (Neurology); Cheryl L. Chrisman, DVM, MS, EDS, DACVIM (Neurology); Caroline N. Hahn, DVM, MSc, PhD, DECEIM, DECVN, MRCVS; Charles M. Hendrix, DVM, PhD; Karen R. Munana, DVM, MS, DACVIM (Neurology); T. Mark Neer, DVM, DACVIM; Charles E. Rupprecht, VMD, MS, PhD; Robert Wylie, BVSc, QDA