PEDIATRICS Vol. 106 No. 5 November 2000, pp. 1093-1096

Blood-Brain Phenylalanine Relationships in Persons With Phenylketonuria

Richard Koch, MD^*, Rex Moats, PhD, Flemming Guttler, MD, PhD^§, Per Guldberg, PhD^§, and Marvin Nelson Jr., MD^*

From the ^* Department of Pediatrics and Radiology, Childrens Hospital of Los Angeles and the University of Southern California School of Medicine, Los Angeles, California;  Deparment of Biology and the Beckman Institute of Technology, Pasadena, California and the Division of Neuroradiology, Childrens Hospital of Los Angeles, Los Angeles, California; and the ^§ John F. Kennedy Institute, Glostrup, Denmark.

	ABSTRACT

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Objectives.  Clinicians caring for persons with phenylketonuria (PKU) have been perplexed by the occasional normal individual with the classical biochemical profile consistent with the diagnosis of PKU. Usually untreated subjects with the biochemical profile of blood phenylalanine (Phe) levels >1200 µmol/L are severely mentally retarded and may have neurological findings. Preliminary reports have recently appeared suggesting that low brain Phe levels, in comparison with elevated blood Phe levels, account for the occurrence of these occasional unaffected individuals with the biochemical profile consistent with PKU.

Method.  Magnetic resonance imaging/magnetic resonance spectroscopy was used to measure brain Phe content compared with simultaneously obtained blood Phe levels determined on the amino acid analyzer. This comparison was obtained in 5 normal non-PKU persons, 4 carriers of the gene causing PKU, and in 29 individuals with the proven form of the disorder.

Results.  Blood-brain measurements in 5 normal persons ranged from .051 to .081 mmol/L, with a mean of .058 mmol/L. Their simultaneously measured brain levels of Phe ranged from .002 to .15 mmol/L, with a mean of .09 mmol/L. Similar measurements were obtained in 4 carriers of the gene causing PKU. Their blood levels varied between .068 and .109 mmol/L, with a mean of .091 mmol/L and simultaneously obtained brain levels of Phe varied between .06 and .21 mmol/L, with a mean of .11 mmol/L. Twenty subjects with a mean IQ of 104 exhibited a mean blood level of 1.428 mmol/L and a simultaneous mean brain level of .23 mmol/L, whereas 9 persons with a mean IQ of 98.7 exhibited a mean blood Phe level of 1.424 and a mean brain Phe level of .64 mmol/L. The correlation between blood and brain levels was not significant.

Conclusion.  In usual cases, intellectually normal persons who have never been treated but who have a biochemical profile consistent with classical PKU exhibit lower brain levels of Phe. Such individuals are exceptional and may not need the vigorous restriction of their blood Phe levels that is required by the majority of persons with PKU.  Key words:  phenylalanine, phenylketonuria, blood, brain, and transport.

Magnetic resonance spectroscopy (MRS) has developed over the past 10 years and has been pioneered by Ross and colleagues.¹ With the recent advances, measurement of phenylalanine (Phe) in brain tissue has resulted in several studies associating low brain levels of Phe with unusual intellectual ability in untreated individuals with elevated blood Phe levels, characterized by classic biochemical phenylketonuria (PKU).^2-9 Ordinarily, untreated adults with PKU are profoundly to severely mentally retarded and have required residential care in public facilities.¹⁰ With the development of the Phe-restricted diet by Bickel et al¹¹ in 1953 and with its use in newborns, a generation of normal individuals with classic PKU has matured into adulthood.¹² There is disagreement as to the proper level of blood Phe control that is necessary for children and adults,^13-23 although nearly all clinicians in the United States caring for children with PKU²⁴ recommend levels between 120 and 360 µmol/L (2-6 mg %). The recent publication by Guttler et al²⁵ documenting an adult Wechsler Adult Intelligence Scale-Revised (WAIS-R) IQ decrease to a mean of 83 in the Maternal PKU Study in women with 2 severe mutations or 1 severe and 1 moderate mutation on both Phe hydroxylase alleles is the strongest evidence to date supporting the concept of the diet-for-life philosophy. In that study, 60% of the adults had discontinued dietary treatment after 6 to 8 years of age. If one now accepts the concept of dietary restriction of Phe into adulthood, the question remains as to what Phe levels should be maintained and how long the diet should be continued. The recent studies on MRI/MRS evaluations in adults⁸ have been suggested as another aid in arriving at logical answers to such questions. This report reviews the results in 5 non-PKU persons, 4 carriers, and 29 individuals with PKU who were initially treated and may provide tentative answers to some of these difficult clinical questions.

	METHODS

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The procedure for MRI/MRS has been well-described.^2-9 This study was approved by the investigational review board of the Childrens Hospital of Los Angeles and an informed consent was obtained from each participant. The 5 controls were recruited from friends of the investigators and were outwardly healthy persons with normal intelligence with a mean age of 27 years (range: 13-50 years). The 4 carriers were 2 parents of PKU persons and 2 offspring of a PKU mother with a mean age of 38 years (range: 12-65 years). The 29 treated individuals with PKU consisted of 22 ingesting a restricted Phe product and 7 on a normal diet at the time of the study. Eighteen were diagnosed by newborn screening, and 11 were diagnosed because of mental retardation. Two adolescents 13 and 15 years old were included in this study at the request of their attending physicians. The other 27 were all over 18 years of age and exhibited a mean age of 29 years. The 22 on a Phe-restricted diet largely demonstrated poor quality control with blood Phe levels greater than our recommended range for adults of 120 to 720 µmol/L but usually <1200 µmol/L (<20 mg %). All but 3 were seen regularly in the PKU program at the Childrens Hospital. The psychological testing was blinded, and the genotypes were performed by the John F. Kennedy Institute (Glostrup, Denmark), using published methods.

	RESULTS

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Table 1 delineates the age and blood and brain Phe levels measured in mmol/L in the 5 controls. Note the variation of brain Phe levels ranging from .02 to .15 in comparison to the constancy of blood Phe levels, ranging only from .051 to .066 µmol/L. The carriers (Table 2) show a wider range of both blood (.068-.109) and brain (.06-.21) concentrations. These variations were perhaps caused by the fact that the subjects had consumed an ad lib breakfast between 7:00 AM and 8:00 AM and were examined between 9:00 AM and 11:00 AM. The rapidity of the absorption of Phe from the bowel into the blood and then into the brain was unknown to the investigators, as was the protein content of the breakfast.

Tables 3 and 4 delineate the extensive data available on the PKU subjects, consisting of sex, age, whether they were diagnosed neonatally, whether they were on a restricted or normal diet, genotype, blood and brain Phe level (mmol/L), WAIS-R score, and whether they were employed. Twenty-seven were white and 2 were Oriental. Table 3 includes 20 subjects with brain levels <.41 mmol/L. These 20 persons averaged 28.5 years of age, with a range of 13 to 49. Eleven were diagnosed by newborn screening and 9 others were diagnosed because of mental retardation. Thirteen have remained on a Phe-restricted diet but with generally erratic control of their blood Phe. Eleven have 2 severe mutations, with a resultant mean IQ of 103. Blood Phe concentrations obtained at the time of the MRI/MRS averaged 1.428 mmol/L, with a range of .47 to 1.776. Brain Phe levels averaged .23, with a range of .10 to .36 mmol/L. The average IQ of all 20 on the WAIS-R was 104, with a range of 78 to 129. Nine were employed full-time, 7 were students, and 3 were unemployed and on welfare. Two of these are mentally unstable and the third, with an IQ of 78, is a homemaker with 4 problem children. There were 5 persons with IQ scores over 115. 

Table 4 delineates the information on 9 subjects with brain Phe levels >.41 mmol/L. The remarkable item of interest is that, despite high brain levels, their intellectual achievement is in the normal range, with a mean of 98.7, which compares favorably with that of the 20 with lower brain levels of Phe. There were no gifted persons in this group. All have remained on a Phe-restricted diet for many years, and only one is unemployed. All 9 of them carry at least 1 severe mutation and 6 of them carry 2 severe mutations of the PKU gene.

	DISCUSSION

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The preliminary reports of untreated persons with PKU achieving normal intellect, despite elevated blood Phe but low brain levels, generated great interest worldwide. Case 2 on Table 3 is such a case; he is 44 years old, married, has an executive position with a good income, and has never been treated. His blood Phe levels are consistently between .900 and 1.200 mmol/L and he exhibits a brain level of only .25 mmol/L. He eats a normal diet with meat and does not exhibit eczema or any neurological problems. It is of interest that there are 5 individuals with IQs >115 in the group with low brain levels of Phe and none in the group with levels >.41 mmol/L.

Guttler et al²⁵ have just published data showing that individuals with 2 severe mutations, who discontinued dietary therapy in childhood, demonstrated a mean IQ of only 83 to 84 and persons with 2 mild mutations demonstrated a mean IQ of 100. The data reported herein do not confirm those findings because the power of dietary therapy obviates the deleterious effects of the 2 severe mutations on the PKU genes.²³ Whether the Phe-restricted diet is sufficient to completely reverse the ill effects of excessive Phe transport into the brain remains to be seen. Most of the PKU persons reported herein are ingesting a Phe-free and tyrosine-enriched product. Because tyrosine competes with Phe transport across the blood-brain barrier, it probably decreases brain content of Phe. Another unanswered question relates to the possibility that Phe transport into the brain may be greater in infancy than in adulthood. It is a well-known fact that a greater degree of mental damage occurs in the first 3 years of life.¹⁶ It is only recently that interest in treating older severely retarded persons with PKU has developed because of the severe behavior disorders that are characteristic of those living in community facilities.^26-28 Preliminary experiences have demonstrated that treatment of even these persons is beneficial. It would be of interest to study brain Phe levels in a group of untreated mentally retarded PKU persons and observe behavioral improvement as brain and blood Phe levels normalize.

	CONCLUSION

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Blood/brain Phe levels are reported in a small number of non-PKU carriers and PKU carriers. Twenty-seven adult persons and 2 children with PKU have also been studied with MRI/MRS and these results compared with achievement in intellect and societal participation. It seems that continued dietary treatment with Phe restriction is beneficial in improving intellectual outcome, particularly in individuals with 2 severe mutations of the Phe hydroxylase gene. Furthermore, MRI/MRS measurements of brain content of Phe seem to be of value in recommending appropriate blood concentrations of Phe for treatment of adults.

	ACKNOWLEDGMENTS

This research was supported by National Institute of Child Health and Human Development Contract NO1-HD-2-3148 to the Childrens Hospital of Los Angeles, the Childrens Hospital Research Institute, and the Danish Medical Research Council, Copenhagen, Denmark.

	FOOTNOTES

Received for publication Jan 26, 2000; accepted Apr 17, 2000.

Reprint requests to (R.K.) Childrens Hospital of Los Angeles, 4650 Sunset Blvd, Los Angeles, CA 90027. E-mail: rkoch8{at}earthlink.net

	ABBREVIATIONS

MRS, magnetic resonance spectroscopy; Phe, phenylalanine; PKU, phenylketonuria; WAIS-R, Wechsler Adult Intelligence Scale-Revised.

	REFERENCES

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1. Ross BD, Freeman DM, Chan L Phosphorous metabolites by NMR. Adv Exp Med Biol 1984; 178:455-464 [Medline]
2. Kries R, Pietz J, Penzen J, Herschkowitz N, Boesch C Identification and quantitation of phenylalanine in the brain of patients with phenylketonuria by means of localized in vivo H magnetic-resonance spectroscopy. J Magn Reson B 1995; 107:242-251 [CrossRef][Medline]
3. Johannik K, Francois B, Marchal G, Localized brain proton NMR spectroscopy in young adult phenylketonuria patients. Magn Reson Med 1994; 31:53-57 [Medline]
4. Ullrich K, Weglage J, Hahn-Ullrich H, Magnetic resonance imaging and proton spectroscopy in PKU. Inter Pediatr 1995; 10:95-99
5. Moller J, Ullrich K, Weglage J, Koch HG, Peters PE In-Vivo NMR Spectroscopy in patients with phenylketonuria: change of cerebral phenylalanine levels under dietary treatment. Neuropediatrics 1995; 16:199-202
6. Pietz J, Schmidt H, Meyding-Lamade UK, Rupp A, Boesch C Phenylketonuria. Findings at MR imaging and localized in-vivo H-1 MR spectroscopy of the brain in patients with early treatment. Radiology 1996; 201:413-420 [Abstract/Free Full Text]
7. Weglage J, Moller, JE, Wiedermann D, et al In-vivo NMR spectroscopy in patients with phenylketonuria: clinical significance of interindividual differences in brain phenylalanine concentrations. J Inherit Metab Dis 1998; 21:81-82 [CrossRef][Medline]
8. Moller HE, Weglage J, Wiedermann D, Ullrich K Blood-brain barrier phenylalanine transport and individual vulnerability of phenylketonuria. J Cereb Blood Flow Metab 1998; 11:1184-1191
9. 9 Moats RA, Koch R, Moseley K, et al. Brain phenylalanine concentration in the management of adults with phenylketonuria. J Inherit Metab Dis 2000; 23:7-14 [CrossRef][Medline]
10. Schuler A, Sowogyi C, Toros I, Twenty years of experience with phenylketonuria in Hungary. Inter J Pediatr 1996; 11:114-117
11. Bickel H, Gerrard JW, Hickmans EM Influence of phenylalanine intake on phenylketonuria. Lancet 1953; 2:812 [CrossRef]
12. Koch R, Fishler K, Azen C, The relationship of genotype to phenotype in phenylalanine hydroxylase deficiency. Biochem Molec Med 1997; 601:92-101
13. Guttler F Hyperphenylalaninemia: diagnosis and classification of the various types of phenylalanine hydroxylase deficiency in childhood. Acta Paediatr Scand 1980; 280:1-80
14. Waisbren SE, Schnell RR, Levy HL Diet termination in children with phenylketonuria: a review of psychologic assessments used to determine outcome. J Inherit Metab Dis 1980; 3:149-153 [CrossRef][Medline]
15. Holtzman N, Van Doorninck W, Azen C, Koch R Effect of age at loss of dietary control on intellectual performance and behavior of children with phenylketonuria. N Engl J Med 1986; 314:593-608 [Abstract]
16. Koch R, Wenz E Phenylketonuria. Annu Rev Nutr 1987; 7:117-135 [CrossRef][Medline]
17. Smith L, Ades AE Intelligence and quality of dietary treatment in phenylketonuria. Arch Dis Child 1988; 65:472-478 [Abstract/Free Full Text]
18. Azen C, Koch R, Friedman EG, Intellectual development in 12-year-old children treated for phenylketonuria. Am J Dis Child 1991; 145:35-39 [Abstract/Free Full Text]
19. Scriver CR, Kaufman S, Woo SLC, Eisensmith RC. In: Scriver CR, Beaudet AL, Valle D, eds. The Hyperphenylalaninemias in the Metabolic and Molecular Bases of Inherited Disease. New York, NY: McGraw-Hill; 1995:1015-1075
20. Fisch RO, Chang PN, Weisberg S, Phenylketonuria patients decades after diet discontinuation. J Inherit Metab Dis 1995; 18:347-353 [CrossRef][Medline]
21. Burgard P, Rupp A, Schneider W, Bremet HF Intellectual development of the patients of the German Collaborative Study of children treated for phenylketonuria. Eur J Pediatr 1996; 155:33-38
22. Weglage P, Peitsch M, Funders B, Guttler F, Harms E Intellectual, neurologic and neuropsychologic outcome in untreated subjects with nonphenylketonuria hyperphenylalaninemia. Pediatr Res 1997; 42:278-384
23. Koch R, Fishler K, Azen C, Guldberg P, Guttler F The relationship of genotype to phenotype in phenylalanine hydroxylase deficiency. Biochem Molec Med 1997; 601:92-101
24. Schuett VE, Brown ES Diet policies of PKU clinics in the United States. Am J Public Health 1984; 7:501-502
25. Guttler F, Azen C, Guldberg P, Romstad A, Relationship between genotype, biochemical phenotype and cognitive performance in the Maternal PKU Collaborative Study. Pediatrics 1999; 104:258-262 [Abstract/Free Full Text]
26. Yannicelli S, Ryan A Improvements in behavior and physical manifestations in previously untreated adults with phenylketonuria using a phenylalanine restricted diet: a national survey. J Inherit Metab Dis 1995; 18:131-134 [CrossRef][Medline]
27. Koch R, Moseley K, Ning J, Long-term beneficial effects of the phenylalanine restricted diet in late diagnosed individuals with phenylketonuria. Mol Gen Metab 1999; 67:148-155 [CrossRef][Medline]
28. Baumeister A Dietary treatment of destructive behavior associated with hyperphenylalaninemia. Clin Neuropharmacol 1998; 21:18-27 [Medline]