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Prenatal Diagnosis: Heredity Disorders, Other Biochemical Diseases, and Disfiguring Birth Defects

There are over 250 recognized sex-linked diseases, affecting every organ system. Of these, 95% affect males, (Emery, 1968). Despite these many sex- linked diseases, at present prenatal diagnosis can specifically be made in fewer than 40 diseases. (Emery, 1968). These sex-linked diseases are individual rare and some are named after physicians who described them, for example, Hemophilia A and B, Duchenne muscular dystrophy, fragile-X syndrome, Fabry disease, Hunter syndrome, Lesch-Nyhan syndrome, and Menkes steely-hair syndrome.

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The following iscourse considers the reasons for the importance of prenatal diagnosis, heredity disorders, and disfiguring birth defects. (Nora,1989). Fabry disease is a biochemical disorder caused by a missing enzyme. (Mulinsky, 1989). A complex fatty substance accumulates in the body because of the missing enzyme which would ordinarily break this compound into pieces. (Nora,1989). This missing enzyme causes kidney and blood-vessel problems that lead to high blood pressure, kidney failure and strokes. (Mulinsky, 1989).

After many years of symptoms, most patients have died in their thirties and orties owing to a lack specific treatment. A biochemical disorder also caused by a missing enzyme is the Lesch- Nyhan syndrome, an extremely unpleasant disorder characterized not only by profound mental retardation and features of brain damage (stiff limbs with peculiar movements), but also self-mutilation, (Jones, 1988). Given good care and attention however, these patients may live on many years in their profoundly retarded state. They often require restraining, tying their hands, to prevent them from mutilating themselves.

Another Affected children with Menkes steely-hair syndrome have hair hat feels similar to steel wool; in addition, they are retarded. The basic defect in this condition concerns the way the body handles copper. Only a few of these sex-linked disorders can now be diagnosed in the fetus, (Stein, 1994). At the present time, the only recourse parents have in the case of sex-linked diseases that are not prenatally diagnosable is to determine the sex of the fetus. If a female fetus is found, the parents can be reassured that their child will not be affected (a critical exception is fragile-X).

However, if it is determined that there is a male fetus present, here is a fifty percent chance that it is affected, (Milunsky, 1989). Since there is no way of being certain, the parents must decide simply on the basis of high risk weather to take a chance or terminate that pregnancy. There are some unusual sex-linked diseases that are confined to females. Disorders of this kind (such as incontinentia pigmenti, a skin disorder associated with brain damage) can be managed by determining weather the fetus is a female. In this group, virtually all females will be affected, and the parents could selective elect to have unaffected boys.

Hemophilia A and Duchenne muscular dystrophy are two of the most common sex-linked diseases that are familiar to most people. But there are so many other diseases that great care must be taken by both the doctor and the family in obtaining an accurate family history. Renpenning syndrome, in which there is mental retardation without any other physical signs, is confined to males. The only way to suspect sex-linked inheritance is for the physician to carefully analyze the family lineage. Tests are preformed to detect female carriers of such diseases.

For example, almost all carriers of hemophilia and Duchenne uscular dystrophy can now be detected. A muscle enzyme, creatine phosphokinase, which leaks into the blood is also often measured to give a higher probability of recognizing a carrier. Unfortunately, because of recombination, the carrier-detection tests for both hemophilia and muscular dystrophy do not provide answers in 100 percent of cases. A negative result causes uncertainty and leaves the question of carrier detection basically unanswered. Fortunately, carrier-detection tests are steadily becoming possible in more of the sex-linked and other disorders.

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