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. The following
discourse 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
forties 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
that 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,
there 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
muscular 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.

Prenatal Studies for Heredity Biochemical Disorders

Many hundreds of different hereditary biochemical disorders of
metabolism are known. About 1 in every 100 children born have one of these
biochemical disorders. (Nora, 1989). Many of these disorders do not cause
mental retardation, or impair the child\'s normal development or general health
to any great extent, if at all. Many others, however, cause severe mental
retardation, seizures, stunting of growth, and early death. Close to 150 of
these biochemical disorders can now be diagnosed in the affected fetus early in
pregnancy. (Nora,1989). The first diagnosis of a biochemical disorder in the
fetus while in the womb was made in the late 1960\'s; the disorder was Tay-Sachs
disease. (Emery, 1968). Diagnosis such as this are made by obtaining cells from
the amniotic fluid which are placed in small dishes containing a nutrient broth,
and then kept in a special warm,