Prenatal Diagnosis Essay, Research Paper
Prenatel DianosisHeredity Disorders, Other Biochemical Diseases, and Disfiguring Birth DefectsThere are over 250 recognized sex-linked diseases, impacting every organ system.Of these, 95 % affect males, ( Emery, 1968 ) . Despite these many sex-linked diseases, atpresent antenatal diagnosing can specifically be made in fewer than 40 diseases. ( Emery,1968 ) . These sex-linked diseases are single rare and some are named afterphysicians who described them, for illustration, Hemophilia A and B, Duchenne musculardystrophy, fragile-X syndrome, Fabry disease, Hunter syndrome, Lesch-Nyhan syndrome, and Menkes steely-hair syndrome. The undermentioned discourse considers the grounds for theimportance of antenatal diagnosing, heredity upsets, and defacing birthdefects. ( Nora,1989 ) . Fabry disease is a biochemical upset caused by a missing enzyme. ( Mulinsky,1989 ) . A complex fatso substance accumulates in the organic structure because of the missingenzyme which would normally interrupt this compound into pieces. ( Nora,1989 ) . Thismissing enzyme causes kidney and blood-vessel jobs that lead to high bloodpressure, kidney failure and shots. ( Mulinsky, 1989 ) . After many old ages of symptoms, most patients have died in their mid-thirtiess and mid-fortiess owing to a deficiency specific intervention. A biochemical upset besides caused by a missing enzyme is the Lesch-Nyhansyndrome, an highly unpleasant upset characterized non merely by profound mentalretardation and characteristics of encephalon harm ( stiff limbs with curious motions ) , but alsoself-mutilation, ( Jones, 1988 ) . Given good attention and attending nevertheless, these patientsmay live on many old ages in their deeply retarded province. They frequently require keeping, binding their custodies, to forestall them from mangling themselves. Another Affected kids with Menkes steely-hair syndrome have hair that feelssimilar to steel wool ; in add-on, they are retarded. The basic defect in this conditionconcerns the manner the organic structure handles Cu. Merely a few of these sex-linked upsets can now be diagnosed in the foetus, ( Stein, 1994 ) . At the present clip, the lone resort parents have in the instance of sex-linked diseases that are non prenatally diagnosable is to find the sex of the foetus. Ifa female foetus is found, the parents can be reassured that their kid will non be affected ( a critical exclusion is fragile-X ) . However, if it is determined that there is a male fetuspresent, there is a 50 per centum opportunity that it is affected, ( Milunsky, 1989 ) . Since there isno manner of being certain, the parents must make up one’s mind merely on the footing of high hazard weatherto take a opportunity or end that gestation. There are some unusual sex-linked diseases that are confined to females.Disorders of this sort ( such as incontinentia pigmenti, a skin upset associated withbrain harm ) can be managed by finding weather the foetus is a female. In thisgroup, virtually all females will be affected, and the parents could selective chosen to haveunaffected male childs. Hemophilia A and Duchenne muscular dystrophy are two of the most commonsex-linked diseases that are familiar to most people. But there are so many other diseasesthat great attention must be taken by both the physician and the household in obtaining an accuratefamily history. Renpenning syndrome, in which there is mental deceleration without anyother physical marks, is confined to males. The lone manner to surmise sex-linkedinheritance is for the doctor to carefully analyse the household line of descent. Trials arepreformed to observe female bearers of such diseases. For illustration, about all bearers ofhemophilia and Duchenne muscular dystrophy can now be detected. A musculus enzyme, creatine phosphokinase, which leaks into the blood is besides frequently measured to give ahigher chance of acknowledging a bearer. Unfortunately, because of recombination, thecarrier-detection trials for both haemophilias and muscular dystrophy do non provideanswers in 100 per centum of instances. A negative consequence causes uncertainness and leaves thequestion of bearer sensing fundamentally unreciprocated. Fortunately, carrier-detection testsare steadily going possible in more of the sex-linked and other upsets. Prenatal Studies for Heredity Biochemical Disorders Many 100s of different familial biochemical upsets of metamorphosis areknown. About 1 in every 100 kids born have one of these biochemical upsets. ( Nora, 1989 ) . Many of these upsets do non do mental deceleration, or impair thechild & # 8217 ; s normal development or general wellness to any great extent, if at all. Many others, nevertheless, cause terrible mental deceleration, ictuss, stunting of growing, and early death.Close to 150 of these biochemical upsets can now be diagnosed in the affected fetusearly in gestation. ( Nora,1989 ) . The first diagnosing of a biochemical upset in thefetus while in the uterus was made in the late 1960 & # 8217 ; s ; the upset was Tay-Sachs disease. ( Emery, 1968 ) . Diagnosis such as this are made by obtaining cells from the amnioticfluid which are placed in little dishes incorporating a alimentary stock, and so kept in aspecial warm, damp brooder. They grow easy. After a period of two to three weeksor, on occasion, every bit long as six hebdomads, there are adequate cells to work on. Each of thecells holding the familial design will demo the specific biochemical defect ( forexample, lacking activity of an enzyme ) thereby enabling a diagnosings to be made. Withdiagnosis, doctors can handle the known upset through the womb.For a few upsets, such as Rh disease, intervention of the foetus straight or throughthe female parent has now succeeded. The first antenatal diagnosing of a biochemical disorderthat was treatable in the uterus was the rare upset methylmalonic aciduria. ( Milunsky,1989 ) . This upset causes failure to boom, purging, lassitude, biochemicaldisturbances, hapless musculus tone, and finally mental and motor deceleration. Treatmentof the foetus through the female parent during gestation is carried out by giving herintramuscular injections of monolithic doses of vitamin B12. This method secures thechild & # 8217 ; s wellness at birth, when a particular low-protein diet is started. In this manner seriousillness, mental deceleration and early decease have been averted. Another well more common upset is inborn adrenal hyperplasia ( CAH ) . This heredity upset is inherited every bit through a cistron from both parents ( autosomal recessive ) . About 1 in 5,000 to 13,000 Whites and 1 in 7550 Nipponese areborn with CAH & # 8211 ; nowhere near the singular 1 in 282 among the Yupik Eskimos. ( Jones, 1988 ) . Assorted signifiers of this upset occur, each due to a deficient, thoughdifferent enzyme along a stepwise tract that eventually consequences in the production of & # 8221 ; Cortone Acetate & # 8221 ; . Symptoms of the most common signifier of CAH are masculinisation of thefemale genitalias, inordinate growing, early visual aspect of pubic hair, and expansion of the
phallus or button. Critically of import in about two-thirds of affected kids is theoccurrence of a dangerous crisis one to four hebdomads after birth, character
ized byvomiting, diarrhea, and salt loss leading to collapse and even death if not diagnosed andtreated with “cortisone”. Where needed, surgical correction of the female genitals ispossible, and normal growth, puberty and fertility can be achieved through lifelongmedical treatment with cortisone like supplements. Today, both carrier detection andprenatal diagnosis are possible for most families, using DNA techniques combined withspecial blood-group linkage studies. The very first inherited biochemical disorder found to cause mental retardationwas phenylketonuria.(Koiata, 1995). Since that description in 1934, it has been learnedthat PKU (phenylketonuria) occurs in about 1 in 14,000 newborns in the United Statesand as frequently as 1 in 4,500 in Northern Ireland.( Nora, 1989). Transmitted by arecessive gene from each parent, all problems are the result of a deficient liver enzyme.An affected untreated child will develop irreversible mental retardation. Therefore, inmost Western countries , blood screening of newborns is done to make an immediatediagnosis and institute the special low-protein diet through which mental retardation canbe avoided. Despite the availability of effective treatment after birth, prenatal diagnosisremains a serious option for parents. This option is valuable because the special lowprotein diet is tasteless and very restrictive.(Mulinsky, 1989). Enforcing the diet in earlychildhood is difficult, and needs to be continued for as long as possible. (Mulinsky,1989). The usual practice has been to discontinue the diet at four to seven years of age.Recent studies show intellectual deterioration, loss of IQ pionts, learning difficulties, andbehavior problems after the diet has been discontinued. (Jones, 1988). A steadilyincreasing number of women with PKU are entering the childbearing years. (Jones,1988). If they become pregnant, the chemical products that accumulate in their blooddamage the fetal brain and other developing organs. Their risk of having a retarded childor one with a heart defect or microcephaly approaches an incredible 100 percent. (Koiata,1995). Only a mere handful of cases are known in which the diet was adhered to strictlybefore conception and a healthy child is born. Today, new DNA techniques have madeboth carrier detection and prenatal diagnosis of PKU possible for most families andtherefore an important decision.(Koiata, 1995). Galactosemia is another treatable hereditary biochemical disease where prenataldiagnosis is possible. If the fetus is affected, special lactose-free dietary treatment of themother started early enough will almost always avert early death or mental retardation,cataracts, and liver damage.(Jones, 1988). There are a few other very rare disorderswhere prenatal diagnosis and early treatment may be critical to save life or preventmental retardation or other consequences. Some of these diseases are: tyrosinemia,homocystinuria, maple-sirup urine disease, and propionicacidemia. (Jones, 1988). A fewother disorders are now being conquered by early diagnosis and treatment in the womb. (Jones, 1988). Continued support for medical research will undoubted provide more andmore opportunities for early treatment or prevention, reducing the need for abortion,which is a major option and issue today. Progress in actual prenatal treatment for geneticdisorders can be anticipated, provided that fetal research is not interdicted by statelegislation. (Nora, 1989). The fact that mental retardation is more common in males has been a known factfor about a century. (Emery, 1968). The major reason for this excess became clear in themid-1970’s, when studies from Australia focused attention on an unexpectedly commondisorder with striking features: the fragile -X syndrome. (Nora, 1989). This disorder,caused by a single defective gene on the X chromosome, has highly variable signs thatusually include mental retardation and distinctive facial features. (Milunsky, 1989).Special studies have revealed the location of the defective gene on the X chromosome: avulnerable spot that tends to break, hence, the term “fragile-X syndrome.” (Milunsky,1989). Because of the remarkable variability of the physical, behavioral, anddevelopmental features of fragile-X syndrome and the delayed appearance of some majorfeatures, definitive recognition of this disorder eluded researchers for many years. (Milunsky, 1989). Confusion was also generated by the fact that although males wereprimarily affected, within the same families mildly affected females were also observed.It is now known that about 1 in 1,060 males are born with fragile-X syndrome, and thatthe disorder accounts for about 25 percent of all male cases of mental retardation andabout 10 percent of mild to moderate mental retardation in females.(Nora,1989). Themain signs of this disorder are on Table 1. Transmission of the fragile-X disorder was initially thought to conform to othersex-linked disorders. Quite unexpectedly, a unique pattern that does not conform exactlyto sex-linked inheritance has been discovered only recently. The current knowledge, asstudied by Dr. Milunsky, allows certain risk predictions:1. An intellectually normal female who inherits the fragile-X gene from hercarrier mother has a 50 percent risk of having an affected son, whose risk of beingretarded is 40 percent . Half her daughters will carry the gene, but only 16 percent willbe retarded. 2. If such a daughter is retarded, her risk of having an affected and retarded son is50 percent. If she has a daughter herself, the risk is 28 percent that the will also bementally impaired. 3. Men who are seemingly entirely normal and do not even show the fragile-Xchromosome when tested may nevertheless transmit the gene to all their daughters.These females are usually intellectually normal. However, when they reproduce, 50percent of their sons will be affected, and 40 percent will be retarded. Half theirdaughters will be carriers, among 16 percent will be retarded. 4. Normal-but-transmitting males may account for 20 percent of all cases of thefragile-X syndrome. Unfortunately, they will remain undetectable until new technologyrevels their ominous burden or until one of their children or grandchildren is diagnosedas having this fateful flaw. 5. Curiously, women carriers who bear a son who is a normal-but- transmittingmale have a 50 percent risk of having an affected male, who has only a 9 percent risk ofbeing retarded. This carrier female also has a 50 percent risk of having carrier daughters,and these girls have only a 5 percent risk of being intellectually impaired. Further research inth this devistating disorder and it’s complex heridaty patternmay significantly reduce the amount of congenital mental retardation. Heredity, biochemical and other disfiguring birth defects must be a top prioritywith expectant parents. A knowledge of these concerns will alolow them to make wisedecisions regarding prenatal diagnosis and decisions and availability of treatment toprevent birth defects, thereby saving lives.