Hereditary Disease
If the mistake can be corrected by a drug or a change in a diet-the person with an inborn defect of metabolism, for example can lead a normal life. Diabetes mellitus is a condition I which the body does not utilize carbohydrates normally. It can be controlled by giving insulin, a hormone that the diabetic does not produce in sufficient quantity.
Phenylketonuria (PKU) is a hereditary disease in which the newborn child cannot properly use part of the protein in milk. If this abnormality goes unchecked, it eventually causes mental retardation. A blood test or a test of a diaper wet by urine shows the doctor whether the disease is present. If it is, the doctor immediately prescribes a special diet to help the child develop normally.
Another important area of genetic research is the detection of carriers of hereditary diseases. The carrier of a recessive gene that causes a hereditary disease is apparently different from the normal person. In the case of phenylketonuria gene, a blood test indicates the individuals with one gene for the disease can be identified, even though they are not sick in any way. Scientists are searching for tests to detect carriers of bad genes, because if one carrier marries another, the chances are one out of four that any child of theirs will have the disease in question.
Marriage between cousins is more likely to produce a child with a hereditary disease. If one partner carries a recessive gene, a member of the same family is more likely than usual to carry it, too. Because the field of hereditary disease is changing so rapidly, parents should discuss any questions with their doctor.
MUTATIONS AND ABNORMALITIES
Occasionally, changes take place spontaneously in genes. This gene is called mutation. A mutant gene is transmitted in the same way that normal genes are. All the bad genes mentioned (those that cause such diseases are haemophilia and diabetes mellitus) arose from mutations.
Radiation from x rays, ultraviolet light and fallout may also cause mutations.
Besides mutations, there are chromosomal abnormalities consisting of too many, too few or altered chromosomes.
Down’s syndrome (Mongolism), a form of mental retardation, is characterized by an extra chromosome or an altered chromosome.
