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

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 an
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