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Congenital and Inherited Disorders Affecting Multiple Body Systems of Cats


Dana G. Allen

, DVM, MSc, DACVIM, Ontario Veterinary College

Reviewed/Revised Aug 2018 | Modified Oct 2022
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A variety of structural and functional defects have been described in animals. These defects are usually classified by the body system primarily affected, and many are discussed under the appropriate body system. Defective newborns have survived a disruptive event during embryonic or fetal development. Defective development may also cause embryonic loss, fetal death, mummification, abortion (a loss of pregnancy or a miscarriage), stillbirth, a newborn not capable of living, or birth defects. A congenital condition is an abnormality present at birth. Other developmental defects may not become apparent until later in life, even though the defect occurred before birth.

Susceptibility to environmental agents or genetic abnormalities varies with the stage of development and species, and decreases with fetal age. The fertilized egg is resistant to agents or factors that cause or increase the rate of occurrence of a congenital defect (teratogens), but it is susceptible to genetic mutations and changes in the chromosomes. The embryo is highly susceptible to teratogens, but this susceptibility decreases with age as the critical developmental periods of various organs or organ systems are passed. The fetus becomes increasingly resistant to teratogens except for structures that develop late such as the cerebellum, palate, urinary system, and genitals.

The frequency of individual defects varies with the species, breed, geographic location, season, and other environmental factors. Among domestic animals, cats have the lowest frequency of congenital defects. Some reported congenital and inherited defects in cats include lack of development of the cerebellum (a part of the brain critical for controlling balance), eye and eyelid defects, heart defects, cleft palate, failure of one or both testicles to descend into the scrotum (known as cryptorchidism), more toes than normal (polydactyly), and diaphragmatic and umbilical hernias. Most congenital defects have no clearly established cause; others are caused by genetic or environmental factors or interaction between these factors.

Polydactyly, cat

Polydactyly, cat

Genetic Factors

Inherited defects resulting from mutant genes or chromosome abnormalities tend to occur in patterns of inheritance. Such patterns include dominant (in which the defect will occur if either parent supplies an abnormal gene to its offspring), recessive (in which both parents must supply an abnormal gene) or others, such as sex‑linked (in which the gene is associated with the X chromosome and not the Y chromosome). In cats, for example, the appearance of excess toes follows a dominant pattern of inheritance, while diaphragmatic hernia follows a recessive pattern.

Calico and Black and Orange Tortoiseshell Cats

Calico and tortoiseshell cats are usually female. The reason has to do with genetics. Normal cats have 38 pairs of chromosomes. Half of these pairs of chromosomes are from the father; half are from the mother. Female cats receive an X chromosome from both the mother and father. (Male cats get a Y chromosome from the father and an X chromosome from the mother.)

The gene that determines the color of a cat’s coat is on the X chromosome(s). Calico and tortoiseshell cats receive one X chromosome with the black coat color gene and one X chromosome with the orange coat color gene. The white coat color seen in calicos and tortoiseshells comes from a different gene. Because 2 X chromosomes are required for the calico and tortoiseshell coats, almost all cats showing these coat colorings are female. Thus, calico and tortoise-shell coat colors are considered to be sex-linked traits.

Very rarely, a calico or tortoiseshell cat is male. These cats are born with 2 X chromosomes (only one of which becomes active) and one Y chromosome. In addition to the rare coat color, the XXY gene defect in male cats also causes sterility.

Some common diseases or disorders caused by genetic defects Metabolic Storage Disorders Metabolism refers to all processes in the body that break down and convert ingested substances to provide the energy and nutrients needed to sustain life. Foods, liquids, and drugs all generally... read more include deficiencies of particular enzymes that lead to the body’s inability to perform normal metabolic functions, and chromosome abnormalities that can result in sterility, abnormal growth, increased embryonic mortality, or reduced litter size. Viruses, certain drugs, and radiation are common causes of chromosomal damage.

The complex interaction between genetic and environmental factors is being studied and is slowly becoming better understood. In general, animals with genetic disorders should not be bred.

Environmental Factors

Factors tending to produce abnormalities of formation include toxic plants, viral infections that occur during pregnancy (such as feline panleukopenia), drugs, chemicals (such as certain herbicides and pesticides), trace elements, nutritional deficiencies, and physical agents such as radiation, abnormally high body temperature, and uterine positioning. Defects may be induced by one or several of these factors. These factors may be difficult to identify, but may follow stress or be linked to maternal disease. They do not follow the pattern of family inheritance that is shown by genetic changes.

Infections of a mother cat during pregnancy can result in miscarriage or congenital defects in the kittens. The mother may or may not show signs of the infection. For example, queens infected with feline panleukopenia virus Feline Panleukopenia Feline panleukopenia (also called feline infectious enteritis or feline distemper) is a highly contagious, often fatal, viral disease of cats. Kittens are affected most severely. Feline panleukopenia... read more during pregnancy can give birth to kittens with congenital cerebellar hypoplasia Cerebellar Disorders 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... read more , a neurologic disorder that results from an incompletely developed cerebellum. These kittens typically have a tremor that does not worsen as the cat matures, and affected animals can be good pets.

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