Cat Genetic Disease

The Austrian empire in the mid-1800s was the important center of the arts, literature, and music. At the same time that Brahms produced his brilliant Variations ona Theme by Handel (1861), another genius, an Austrian monk named Gregor Men-del, was making one of the most important biological discoveries ever made: anorganism's traits, such as height, are regulated by two particles we now know asgenes (Greek for "to give birth to"), one particle contributed by the female and theother by the male. Mendel performed his experiments on garden pea plants. Henoticed that when he bred tall pea plants to short pea plants, all the offspring weretall. Mendel called this characteristic the dominant trait, and the characteristic that"seemed to disappear," to termed recessive.

When Mendel bred the offspring to each other, the result was three tall peaplants for every short pea plant a ratio of three to one. Mendel surmised thateach offspring of the first breeding carried one dominant and one recessive particleand that in the breeding of the offspring, one short pea should be produced forevery three tall pea plants.

Unfortunately, Vienna and the rest of the world neither understood nor caredabout the biological sciences, which were considered antireligious. Gregor Men-del's papers were burned after his death in 1884, and his great findings were not"rediscovered" until the beginning of the twentieth century.

What is this genetic material, which determines that like shall beget like?Genes are composed of deoxyribonucleic acid (DNA). This DNA is found in longstrands called chromosomes in the nucleus of the billions of cells in your pet'sbody. Every cell of your cat contains nineteen pairs of chromosomes.

Each gene controls the synthesis of one protein. Protein makes up aboutthree-fourths of the body solids and is the building block of life. The majority ofproteins are enzymes that regulate the chemical reactions in the cells. Blood, bone,hair, and muscle are primarily protein. Hormones such as insulin are also proteins.Structural protein called connective tissue gives the skin its elasticity and the hairits form.

Throughout a lifetime there is a constant turnover of cells - daily wear andtear destroy skin, hair, and blood cells, but they are constantly being replaced,thanks to the cells' ability to duplicate themselves. Before the cell divides, thechromosome forms a replica of itself (a process called replication). Each new cellhas the exact number and order of genes as the original cell. Thousands uponthousands of activities occur and renew themselves daily in your pet's body, thanksto a biological "blueprint," called the genetic code, in the chromosomes.

Every part of your pet's body (and even its temperament, to a large extent)is dependent on the chromosomes that were combined when its parents mated.The fertilized egg is a complete cell containing all the information that determineshereditary makeup. That cell divides in the mother cat's uterus, and the developingembryo contains the identical genetic makeup.

Let's suppose you bred your pure tabby to a pure black cat. What color wouldyou expect in the kittens? Tabby is dominant, and black is recessive. If a creaturehas two dominant genes for a trait, such as tabby. it is called homozygote. Let'suse the letters TT for our homorygote female's genes, and tt for the male's reces-sive black-coat genes. The kittens will all have one gene from each parent (Tt); thispairing of dominant and recessive genes is called heterozygote. Because tabbygenes are dominant, all the kittens will be tabby. What if you bred one of thesekittens to another heterozygote just like it?

Mendel's Checkerboard Mother's eggs

In the next generation, one of four kittens will have dominant tabby genes,two will be tabby heterorygotes like their parents. and one will have a pair of theparents' recessive black-coat genes. In other words, two tabby parents can producea black cat!

By now, you're probably wondering what all this has to do with your cat'shealth. It has a lot to do with it! As you already know, one gene carries the messagefor the production of one protein. But if the DNA gets mixed up. the gene carriesan abnormality known as a mutation, a change from the normal pattern of inheri-tance that appears as a new or altered characteristic.

Inbreeding (mating closely related individuals, such as mother to son, fatherto daughter, or brother to sister) or linebreeding (mating more-distant relativessuch as cousins) increases the chance of defects that require two recessive genesto come together or defects that require a polygenic union. Before breeding, themale and female should be checked by a veterinarian for defects or diseases thathave a hereditary basis.

A disease called globoid cell leukodystrophy has been seen in a few kittens inwhich a genetic enzyme deficiency causes progressive degeneration of the nervoussystem and death in kittens between two and six months of age. It has a recessivepattern of inheritance: i.e., a kitten must receive two abnormal genes to producethe disease. A cat that has one normal gene and one abnormal gene is called a heterozygote carrier and will appear normal but can pass the abnormal gene to itsoffspring.

At the University of Pennsylvania Veterinary School, Doctors Donald Patter-son and Peter Jezyk and their co-workers are studying the "fading puppy syn-drome: In human neonates and infants, genetic enzyme defects such asphenylketonuria (PKU) have been identified. Newborn infants can be screened forthese hereditary metabolic defects and treated before mental retardation, liver orkidney dysfunction, or death occurs. Neonatal kittens that fail to thrive (they loseweight, have problems moving, and can't maintain body temperature) may havesimilar disorders.

Metabolic screening is a new and important procedure in veterinary medi-cine. Dr. Jezyk points out, "In human medicine, 5 to 10 percent of all admissionsto pediatric hospitals are for disorders which are clearly genetic, while another 10to 15 percent are for conditions with some genetic component." The developmentof veterinary clinical specialties such as neurology, cardiology, dermatology, andophthalmology has increased the accuracy of diagnosis and the recognition of ge-netic diseases. Improved methods of both prevention and treatment of parasitic,nutritional, and infectious diseases have decreased the importance of these ill-nesses and have brought to light diseases that are entirely or partially genetic inorigin.