Counseling in medical genetics / Sheldon Reed.

  • Sheldon Clark Reed
Date:
[1980]
Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Counseling in medical genetics / Sheldon Reed. Source: Wellcome Collection.

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    56 / Treatment for Some Genetic Diseases that of the normal population, they are educable at regular schools and differ strikingly from most untreated phenylketonuria children whose mean IQ is about 50. It is thought that high phenylalanine early in hfe can cause marked changes in the composition of the brain and that it inhibits the transport and concentration of other amino acids in liver and brain. Actually the cause of the mental retarda¬ tion is far from understood. The dietary treatment of a metabolic disorder such as PKU is highly complex and potentially hazardous. Presumably no physician would embark on the care of such patients unless he or she is able to work closely with a dietician experienced in the treatment of the trait. For the best resuhs the babies should be treated in centers designed for the purpose. The length of each admission should be kept short and there should be good cooperation among all concerned. There are two religions in the United States as to how long the patient should be kept on the low phenylalanine diet. One states that females should be kept on the diet until menopause, but the other realizes that some more realistic stopping point must be accepted. Once the child is off the diet and has experienced the joys of ad lib eating, it is difficult for him to get back on the diet. The children born to mothers with untreated phenylketonuria have a very high incidence of congenital abnormalities, including mental retardation. These children are obligate carriers of the gene for PKU, and ordinarily would not be affected. However, the high phenylalanine levels of the mother, to which they are subjected in utero, cause irreversible damage to their brains. The only solution for homozy¬ gous mothers with high phenylalanine levels is planned pregnancy with dietary restriction throughout the pregnancy. The diet during pregnancy presents many problems and is potentially hazardous. The reader is referred to the book edited by Raine [1975] for a more detailed treatment of these problems. Homocystinuria There are two main approaches to treatment for Mendelian recessive gene defects. The first is the restriction of substrate accompanied by product replace¬ ment as in PKU, and the second is by co-enzyme supplementation. In the latter case the defect may be in the vitamin precursor of the co-enzyme. Homocystinuria is an example of a trait which can be influenced by supplementation with vitamin Вб. Pyridoxal phosphate is the most important active form of the vitamin, which as co-enzyme takes part in a variety of enzymatic reactions involving amino acids. There is no evidence of any deleterious effect of high doses of pyridoxine given over prolonged periods, either to children or during pregnancy. Therefore, upon diagnosis of a patient with homocystinuria, a trial of pyridoxine should be given irrespective of age. It should be known within three weeks if the patient is respond¬ ing to the treatment. We cannot go into the details of testing and treatment here, and again refer the reader to the book edited by Raine [1975].
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