Volume 121
`Number 2
`
`Clinical and laboratory observations
`
`259
`
`Plasma glutamine concentration: A guide in the
`management of urea cycle disorders
`
`NancyE. Maestri, PhD, Kathryn D. McGowan, mpD,* and SaulW. Brusilow, MD
`From the Department of Pediatrics, Jonns Hopkins School of Medicine, Baltimore, Maryland
`
`Becauseincreasesin plasma giutamine concentrations are almost always as-
`sociated with hyperammonemia in patients with urea cycle disorders, we deter-
`mined the correlation between these two variables for 2 years in a child with or-
`nithine transcarbamylase deficiency. Acorrelation coefficient of 0.77 (p <0.0004)
`was found. Hyperammonemia was rarely observed when plasma glutamine
`levels were near normal. These data suggest that one goal of therapyis the
`maintenance of plasma glutamine levels at or near normal values. (J PEDIATR
`1992;424:259-64)
`
`
`
`The presence of hyperglutaminemia in hyperammonemic
`patients with urea cycle disorders has been knownsince the
`earliest case reports! and is another manifestation of the
`disorder of nitrogen homeostasis.*? Moreover,
`in two
`patients with ornithine transcarbamylasedeficiency, plasma
`glutamine levels increased before the onset of hyperam-
`monemia.* Hyperglutaminemiais also associated with the
`hyperammonemia of severe liver disease’ and Reye syn-
`drome.® On the basis of these observations,
`this study
`examined the relationship between the plasma glutamine
`and ammonium concentrations during a 24-month period in
`one patient with the neonatal form of OTC deficiency.
`CASE REPORT
`
`The patient was the younger brother of a boy with OTC
`deficiency who, after rescue from neonatal hyperammonemic
`coma, was profoundly developmentally delayed and died in hyper-
`ammonemic comaat age 16 months of age. The mother was iden-
`tified as a carrier of the mutation at the OTC locus on the basis of
`
`the diagnosis of the proband and a positive protein tolerancetest
`result. More recently, the mutation in this pedigree has been iden-
`tified as a T—Csubstitution in theinitial dinucleotide ofintron 7,
`resulting in a deletion of exon 7.’ The family waslost to follow-up
`until the mother was 26 weeks’ pregnant with a fetus of unknown
`
`Supported by National Institutes of Health grants HD 11134, HD
`26358, and RR 00052, U.S. Food and Drug Administration grant
`No. FD-R-000198, the T. D. and M. A. O’Malley Foundation, and
`the Kettering Family Foundation.
`Submitted for publication Nov. 15, 1991; accepted Feb. 25, 1992.
`Reprint requests: Saul W. Brusilow, MD, Department of Pediat-
`rics, Johns Hopkins School of Medicine, 600 N. Wolfe St., Park
`Building Room 336, Baltimore, MD 21205.
`*Now at the Department of Obstetrics and Gynecology, Johns
`Hopkins School of Medicine, Baltimore, MD 21205.
`9/22/37448
`
`gender. After genetic counseling, during which the options for di-
`agnosis and treatment weredescribed,* the family chose delivery
`at their local community hospital and declined to enter the infant
`into an experimental diagnostic and treatment protocol. After de-
`livery, notwithstanding the earlier decision, the apparently healthy
`term male neonate was not fed enterally but was given only intra-
`venousfluids including 10% glucose solution. On discharge from
`the community hospital when the infant was 48 hoursof age, the
`parents chose to seek therapy and the patient was broughtdirectly
`to Johns Hopkins Hospital. On arrival he was lethargic and had
`plasma ammonium and glutaminelevels, respectively, of 117 and
`2074 wmol/L (normal values <30 and 613 + 15)%; plasmacitrul-
`line was undetectable. He also had a plasmaorotate level of 2:13
`
`OTC Ornithine transcarbamylase
`
`pmol/L (undetectable in normal neonates [Brusilow SW: unpub-
`lished observations]) and a respiratory alkalosis. After. further
`counseling, the parents gave informed consent for the patient’s en-
`try into a study evaluating the intravenous dosage form of benzoate
`and phenylacetate, and long-term therapy with the oral dosage
`form of sodium phenylbutyrate. At 24 and 48 hours after intrave-
`nous therapy,!° the patient’s plasma ammonium levels were,
`respectively, 31 and 24 pmol/L.
`In the subsequent 2 years the patient has been treated with a low
`protein diet (at times supplemented with essential amino acids),
`L-citrulline, 175 mg/kg per day, and sodium phenylbutyrate, 500
`to 600 mg/kg per day. The details and variations of this protocol
`are described elsewhere.!° On the Cattell Infant Intelligence Scale
`his development quotient was 80 at 19 months of age. The patient
`is at the 25th percentile for weight and below the 3rd percentile for
`height. He has been admitted to the hospital three times because
`of symptomatic hyperammonemia.
`
`METHODS
`
`During the 2-year follow-up period, 57 measurements
`were madeof plasma ammonium and aminoacid levels. In-
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`

`260
`
`Clinical and laboratory observations
`
`The Journal of Pediatrics
`August 1992
`
`
`
`
`
`PlasmaGlutamine(uM)
`
`2400
`
`2100
`
`1800
`
`1500
`
`1200
`
`900
`
`600
`
`300
`
`
`
`60
`
`90
`
`120
`
`150
`
`Piasma Ammonium (uM)
`
`
`
`The findings of a weaker correlation between plasma
`ammonium and glutamine levels when plasma ammonium
`levels are normal are consistent with the hypothesis that in-
`creased plasma glutamine levels are forerunners of in-
`creased plasma ammoniumlevels.* These data, in conjunc-
`tion with the reports cited earlier, suggest that glutamine
`may represent a storagesite for nitrogen accumulation. The
`precise capacity of glutamine to serve this function is
`unknown,but it appears that as plasma glutaminelevels in-
`crease to greater’than normal, there is a greaterlikelihood
`of hyperammonemia. Although the plasma level of glu-
`tamine above which ammonium accumulatedin this patient
`was approximately 1000 umol/L, our random observations
`of other patients suggest, as might be expected, that there
`maybe considerable individualvariability of this threshold.
`These data have potentially useful monitoring and ther-
`apeutic implications. They suggest that increasing plasma
`glutamine levels may indicate that dietary or drug therapy
`requires modification. Such modifications include an in-
`creased dose of phenylbutyrate, an increased calorie intake,
`a reduction of total nitrogen intake, and redistribution of
`nitrogen intake between natural protein and essential amino
`acids to take advantageof the lower nitrogen density of es-
`sential amino acids.
`
`Figure. Relationship between plasma glutamine and ammonium concentrations. For all values the Pearson correlation
`coefficient is 0.77 (p <0.0001). For plasma ammonium valuesless than 30 wmol/L (p = 0.436; p <0.0001).
`
`high. Furthermore, the height of the plasma ammonium
`. level was strongly correlated with the height of the plasma
`glutamine concentration.
`
`DISCUSSION
`
`cluded in this study are those values obtained during all
`outpatient visits. Plasma ammonium levels were measured
`by a cation exchange-visible spectrophotometric tech-
`nique,!! and plasma amino acids were measured by auto-
`mated column chromatography using a Beckman model
`6300 amino acid analyzer (Beckman Instruments, Inc.,
`Brea, Calif.). Apart from the initial sample, blood wascol-
`lected from the patient during daytime hours (plasma glu-
`tamine levels are lowest then in patients treated with this
`protocol!?), Blood was placed in heparinized tubes and im-
`mediately chilled on ice, and the plasma was promptly sep-
`arated in a refrigerated centrifuge and analyzed immedi-
`ately or frozen for analysis within 24 hours.
`
`RESULTS
`
`The relationship between plasma levels of ammonium
`and glutamine in this patient is shown in the Figure. The
`Pearson correlation coefficient for all values of glutamine
`and ammonium wascalculated as 0.77 (p <0.0001), When
`plasma ammonium levels were within the normal range
`(<30 pmol/L), glutamine levels varied between 145 and
`1090 pmol/L and were more weakly correlated with plasma
`ammonium levels (o = 0.436; p <0.0001).
`Plasma glutamine measurements were grouped into six
`strata, and the mean glutamine and‘4rimoniumlevels were
`calculated. As shown in the Table, the mean ammonium
`level was normalfor glutamine values less than 800 umol/L;
`however, when plasma glutaminelevels increased above this
`level, an increasing percentage of ammonium levels. were
`
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`

`Volume 121
`Number 2
`
`Clinical and laboratory observations
`
`261
`
`Table. Number of high (>30 wmol/L) plasma ammonium levels for specified plasma glutamine levels
`
`Mean Gin
`Range of Gin
`(umol/L)*
`fn
`«amot/L)
`295 + 62.8
`12
`200-400
`8
`L
`21.8 + 7.0
`6
`1
`21.3 4 4.8
`503 + 61.3
`16
`401-600
`690 + 51.8
`13
`601-800
`0
`0
`21.5 441
`40
`2
`34.8 + 15.4
`892 + 66.8
`5
`801-1000
`1190 + 84.0
`7
`1001-1400
`86
`6
`55.0 + 36.3
`
`
`
`4 1829 + 302.8>1400 100 110.8 + 40.4 4
`
`
`
`Mean NH,+
`(umol/L)*
`
`No.
`
`%
`
`NH,* >30 uwmol/L
`
`
`
`cirrhosis: relation to other manifestations of liver disease.
`Gastroenterology 1978;75:570-9.
`. Romshe CA, Hilty MD, McClung J, Kerzner B, Reiner CB.
`Amino acid pattern in Reye’s syndrome: comparison with
`clinically similar entities. J PEDIATR 1981;98:788-90.
`. Carstens RP, Fenton WP, Rosenberg LF. Identification of
`RNAsplicing errors resulting in ornithine transcarbamylase
`deficiency. Am J Hum Genet 1991;48:1105-14.
`. Maestri NE, Hauser ER, Bartholomew D, Brusilow SW.Pro-
`spective treatment of urea cycle disorders. J PEDIATR 1991;
`119:923-8.
`. Batshaw ML,Brusilow SW. Asymptomatic hyperammonemia
`in low birth weight infants. Pediatr Res 1978;12:221-4,
`Brusilow SW. Treatment of urea cycle disorders. In: Desnick
`R, ed. Treatment of genetic diseases. New York: Churchill
`Livingstone 1991:79-94,
`Brusilow SW. Determination of urine orotate and orotidine
`and plasma ammonium. In: Hommes FA, ed. Techniques in
`diagnostic human biochemical genetics. New York: Wiley
`Liss, 1991:345-57.
`Brusilow SW. Phenylacetylglutamine may replace urea as a
`vehicle for waste nitrogen excretion, Pediatr Res 1991;29:147-
`50.
`
`10.
`
`Li.
`
`12.
`
`13.
`
`14.
`
`Hawkins RA,Jessy J. Hyperammonemia does not impair brain
`function in the absence of net glutamine synthesis. Biochem J
`1991;27:697-703.
`Takahashi H, Koehler RC, Brusilow SW, Traystman RJ. In-
`hibition of brain glutamine accumulation prevents cerebral
`edema in hyperammonemic rats. Am J Physiol 1991;
`261:H825-9.
`
`Gin, Glutamine; NH,*, ammonium.
`*Values are mean + SD.
`
`These findings may have broadersignificance in view of
`recent reports suggesting that glutamine may be more
`closely related to the pathophysiology of the encephalopa-
`thy of hyperammonemia than is ammonium.!*!4
`
`Wethank the nursingstaff of the pediatric clinical research unit
`for their help in obtaining plasma specimens. Wealso thank Mrs.
`Ellen Gordes for her expert technical assistance in performing
`measurements of plasma ammonium.
`
`REFERENCES
`
`L.
`
`2.
`
`Levin B, Oberholzer VG, Sinclair L. Biochemical investiga-
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`. Arn PH, Hauser ER, Thomas GH, Herman G,HessD,Brusi-
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`. Ansley JD, Isaacs JW, Rikkers LF, Kutner MH, Nordlinger
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