Section 15 — Human Genetics 



avoid or improve phenylketonuria or phenyl- 

 pyruvic idiocy when the children affected with 

 this recessive hereditary disease are fed with a 

 phenylalanine-poor diet from the first months of 

 life. Therefore it is very important to detect this 

 disease at its very beginning by means of a 10 

 per cent ferric chloride solution added to the 

 urine. If there is any phenylpyruvic acid, the 

 yellow color of the urine becomes rapidly and 

 intensively green. 



Moreover, as soon as the disease is discovered 

 in a family, it would be desirable, on the one 

 hand to determine the other diseased persons 

 and, on the other hand the people who are 

 carrying the deleterious gene (heterozygotes) and 

 are likely to pass on the disease to their children 

 if they marry another heterozygote. 



Using the microbiological process, elaborated 

 by Knox and Messinger, to determine the fasting 

 phenylalanine level in blood plasma, the authors 

 were able to find out with sufficient accuracy the 

 gene carriers in the successive generations of 

 three families where a phenylpyruvic idiot was 

 first seen. 



The average fasting level of plasma phenyla- 

 lanine was found to be at 80.33 micromoles per 

 liter, ± 9.67 with normal individuals where as 

 the average level with carrier people amounted 

 to 104.47 micromoles per liter, ± 10.88. 



The meaning of the intermediate values be- 

 tween these two figures can be better estimated by 

 an oral phenylalanine load test on some in- 

 dividuals. 



groups and the influence of sex, age, body weight, 

 etc., upon the segregation between the two 

 groups. 



15.65. Phenylketonuria: Further Studies on the 

 Heterozygous Carrier. William F. Rowley, 

 Margaret E. O'Flynn, and Paul Wong 

 (Chicago, U.S.A.). 



The present paper will describe a series of 

 studies carried out using more sensitive and 

 accurate fluorimetric methods for the assay of 

 phenylalanine and tyrosine in the serum. 

 Phenylalanine levels were determined on 0.05 ml 

 serum using a modification of the fluorimetric 

 method of McCaman and Robbins.f 1 ) Tyrosine 

 values were obtained from 0.02 ml serum from a 

 procedure adapted from that suggested by 

 Waalkes and Udenfriend.( 2 ) 



One hundred parents of phenylketonuric 

 children and an equal number of controls were 

 given 0.1 gm per kg L-phenylalanine by mouth. 

 Blood samples were obtained at 0, 1 , and 2 hours 

 after the load and analyzed for both phenylala- 

 nine and tyrosine. The data are analyzed in terms 

 of the best discriminant for separating the two 



1. J. Lab. & Clin. Med. 59, 885, 1962. 



2. J. Lab. & Clin. Med. 50, 733, 1957. 



15.66. Frequency of Phenylketonuria. 



Robert Guthrie (Buffalo, U.S.A.). 



The principle upon which the "inhibition as- 

 say" is based can be applied to the detection of 

 various "inborn errors of metabolism"^ 1 ) 

 In one application, a microorganism and a 

 specific inhibitor are incorporated in a layer of 

 agar culture medium. Upon the surface are 

 placed rows of paper discs punched from filter 

 paper containing dried blood spots or urine. 

 After incubation, the diameters of the growth 

 zones for the unknowns are compared to dia- 

 meters of zones surrounding "control" discs. 

 For example, azaserine and Bacillus subtilis can 

 be used in this way to detect histidinemia. For 

 phenylketonuria, B-2-thienylalanine and Bacillus 

 subtilis spores are used to test dried spots of 

 blood collected upon filter paper by heel punc- 

 ture of newborn infants before leaving the hos- 

 pital nursery. A brief description of this technic 

 will be presented. 



With the demonstration by the Massachusetts 

 Department of Health that this method is prac- 

 tical for routine screening for phenylketonuria 

 in newborn infantsC 2 ) it will now be possible 

 for the first time to estimate the true frequency 

 of this disease within the populations screened. 

 The first 74,000 tests carried out by forty labora- 

 tories in 29 states (including Massachusetts) 

 have detected seven cases. The Massachusetts 

 Department of Health has detected five of these 

 cases in that State among the first 27,000 new- 

 born infants tested. At the present time (Febru- 

 ary 1963), 25,000 total tests are conducted per 

 month, and the rate of testing is increasing 

 rapidly. A recent progress report of this program 

 will be presented. It appears that the frequency 

 of this disease may be greater in the populations 

 so far screened than the highest frequency 

 usually given, 1/20,000. An estimate of the fre- 

 quency of this disease will be attempted from the 

 latest results available. 



The "inhibition assay" method of testing will 

 detect PKU cases in which the urine does not 

 react to ferric chloride, as in young infants. 

 However, this condition is known to exist 

 also in some adults ("PKU without PKU"), 

 but their frequency is unknown. This type of 



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