49

Clinica Chimica Acta, 63 (1975) 49-54 0 Elsevier Scientific Publishing Company,

Amsterdam

- Printed in The Netherlands

CCA 7217

INTERPRETATION IN CHILDREN

OF ELEVATED BLOOD GLYCINE LEVELS

DEREK A. APPLECARTS

and STELLA POON

Department of Paediatrics, University of British Columbia and Children’s Hospital, Vancouver, B.C. (Canada) (Received

March 15, 1975)

Summary Recent experience with three children who had non-ketotic hyperglycinemia suggested that interpretation of blood glycine levels in children is complex. The elevations of blood glycine in these children were quite modest, and comparable to those of other children admitted to hospital with other diseases. Often we find elevations of blood glycine in children who have had some degree of starvation before blood was taken for amino acid analysis. In a “typical” patient, valine, leucine, isoleucine and occasionally threonine are depressed, while the glycine level is raised. As nutrition improves all of these amino acids return to normal. Our data suggest that blood glycine levels in children with an acute episode of a debilitating disease need to be interpreted with respect to the immediate state of nutrition of the children. Introduction Interpretation of blood glycine levels in children can be difficult. When patients with non-ketotic hyperglycinemia are investigated in the newborn period, the plasma glycine levels are often hard to interpret. In two of three patients that we examined, the presenting plasma glycine levels were no higher than levels we have found in other children, although in both patients the plasma glycine levels did become much more abnormal later, Two other patients, one of whom presented with an undiagnosed encephalopathy at 1 year of age and the other of whom presented with fever, a convulsive disorder, gastroenteritis and shock at 5 months of age were investigated co-incidentally and had higher glycine levels than the patient with proven non-ketotic hyperglycinemia. These two other children also had low levels of valine, leucine and isoleucine. As they were followed over a period of three to four weeks, the clinical condition of both children slowly improved and the amino acid values slowly returned to normal until at the time of discharge of the children, after

50

about one month, they were entirely normal. Both of these children had had a period of several weeks starvation and considerable weight loss before being admitted to hospital and both required therapy with intravenous solutions for approximately the first week of their admission. As their diet improved so did their plasma aminograms. These findings directed our attention to elevations of blood glycine in other children who had periods of poor diet prior to investigation. Elevation of plasma glycine levels and depression of branched chain amino acid levels seems to be a characteristic finding in starving children who may be admitted to hospital for investigation. This communication reports our findings in such children. Methods Amino acids were measured using a Beckman 120C amino acid analyser (Beckman Spinco Instruments, Palo Alto, California). Fasting blood samples were taken, after a six hour fast from children who were on four hourly feedings and after a twelve hour fast for older children. Heparinized blood was collected, the plasma separated from the samples immediately. The plasma was then deproteinized, using 30 mg of sulfosalicylic acid per ml of plasma. The diagnosis of non-ketotic hyperglycinemia was made by measuring labelled expired carbon dioxide, following injection of glycine labelled with 14C in the carboxyl group [l]. In two of the three cases confirmation of the diagnosis was made by enzymatic assay of the glycine cleavage enzyme system in post-mortem tissue samples [Z] . Urinary organic acids were examined by Mrs S. Hansen [ 21.

.=JTQ

n =M.T.? A=D.L.B.~

Fig. 1. Initial amino acid levels in 3 patients

with non-ketotic

hyperglycinemia.

51

m =

Normalrange

Fig. 2. Amino acid levels in patient R.J.

Results The initial amino acid values on three patients with non-ketotic hyperglycinemia are shown in Fig. 1. At the time the blood samples were taken J.T. was age 7 weeks, M.T. was age 5 days and 16 days respectively, and D.L.B. was aged 4 weeks. J.T. and M.T. were sisters. The ammo acid values of patient R.J. who presented with an undiagnosed encephalopathy at 1 year of age are shown in Fig. 2. The amino acid levels of patient SC. who presented with fever, a

Normal range Fig. 3. Amino acid levels in patient SC.

m Fig.

4. Amino

acid

levels

in patient

= Normal

range

C.D.

convulsive disorder, gastroenteritis and shock at 5 months of age are shown in Fig. 3. Fig. 4 shows the amino acid values of patient C.D. who had cystic fibrosis and whose clinical history is described in the discussion. Discussion Patients J.T. and D.L.B. were diagnosed in the newborn period as a result of a urine screening program. The amino acid values illustrated in Fig. 1, show the presenting blood glycine levels were not remarkably elevated. Later blood glycine levels were much higher and it was then possible to confirm the diagnosis of non-ketotic hyperglycinemia by injection of labelled glycine. However, the presenting blood glycine levels of two children who were also being investigated at the same time, patients R.J. and S.C., were of the same order of magnitude or even higher than those of our three patients. Both of these patients were admitted to hospital at the same time with illnesses that needed extensive investigations. The three patients with non-ketotic hyperglycinemia had clinical courses that did not improve whereas the other two patients did return to normal during the period of their hospitalization. However, they had both presented as diagnostic problems for laboratory evaluation and the interpretation of their initial blood glycine levels was of some concern to us. In searching for a cause for the abnormalities in blood ammo acid levels, it seemed appropriate to look at the effects of starvation on blood amino acid levels. R.J. had a period of several weeks starvation with considerable weight loss before being admitted to hospital. SC. was starved for many days prior to admission. Both required therapy with intravenous solutions for approximateiy the first week of their admission. As their diet improved so did their aminograms. Neither SC. nor R.J. had any metabolic acidosis and we do not believe that either chiId had ketotic hyperglycinemia. The urine of S.C. was checked

53

for propionic and methylmalonic acid and neither was detected [2 1. In retrospect the cause of hospitahsation in SC. was probably gastroenteritis leading to hypoglycemia, shock and a left-sided infarction in the brain. R.J. is now well and her illness remains undiagnosed. It had none of the criteria for Reye’s syndrome . Table I shows the effect of both protein-calorie malnutrition and total calorie restriction on blood amino acid levels in adults. This table is compiled from Adibi et al. [3,4] and Felig et al. [5]. These figures are on adults but similar results have been reported in articles in which children suffering from severe malnutrition have been investigated [6-81. It seems likely that the blood glycine levels that we obtained on the two patients R.J. and S.C. were caused by the immediately preceding period of starvation prior to the amino acid measurements. The problem of interpretation was compounded for these two children by the scarcity of information on normal values in the age period between 6 months and 6 years. The normal values quoted in Figs 2 and 3, come from the work of Ghadimi and Pecora [9] and Soupart [lo]. These two articles contain values for children in this age group which encompass only twenty-nine subjects. There are excellent normal values to be found in the literature for values of free amino acids in newborn subjects [ll],subjects up to 3 months of age [ 121, and for children who are aged 6 to 18 years [13], but it is very hard to find in the literature, or indeed to find in one’s every day work experience, normal values on children aged between 3 months to 6 years of age. The upper and lower limits of normal values shown in Figs 2 and 3, are therefore not clearcut. Since we investigated these children, we have investigated similar examples in our laboratory. As a further illustration of this Fig. 4 shows blood amino acid values on an adult patient aged 20 years, who had cystic fibrosis and in whom esophageal surgery had been performed. An esophageal stricture made it difficult for the patient to eat and led to a period of semi-starvation. His

TABLE I EFFECTS OF TOTAL CALORIE MALNUTRITION DEPRIVATION ON BLOOD AMINO ACID LEVELS

(STARVATION)

AND ISOCALORIC

PROTEIN

For the source of these comments see the text. Amino acid

Starvation Days 7-21

Days l-6

Days 7-21

t t t t

-Normal -Normal -Normal -Normal

Sl. Sl. Sl. Sl.

j. J -1 J

-Normal -Normal -Normal -Normal

f

Sl. t t t I Sl. t

Sl. f -Normal f t Sl. t

Sl. f -Normal f f Sl. 1

Days l-6 Valine Leucine Isoleucine o!-Amino-n Butyrate Methionine Threonine Glycine Alanine Serine

Sl.

Iso-caloric protein deprivation

Sl. J -Normal 4 -Normal

54

plasma aminogram shows elevations of blood glycine and decreases in valine, leucine and isoleucine. We have noticed similar findings in patients with other debilating diseases such as the Jansky-Bielschowsky syndrome in which no disorders of glycine metabolism can be implicated. We also notice elevations of blood glycine in renal patients being peritoneally dialysed. In renal patients, however, the elevation of blood glycine is also linked to an elevation of citrulline and is not usually associated with a depression of the branched chain amino acids. The point that we make here is that diseases other than those of primary glycine metabolism can be associated with high glycine levels. It does seem possible to predict in children suffering from an acute illness, whether an elevation of glycine is caused by starvation or by a disorder of glycine metabolism. This can be done by assessing the level of glycine relative to the levels of valine, leucine and isoleucine. In the three patients with nonketotic hyperglycinemia, whose results are shown in Fig. 1, the elevations of blood glycine are not associated with decreases in the levels of branched chain amino acids as was seen in the others. It seems clear that blood glycine levels obtained in children need to be interpreted with respect to the immediate state of nutrition of the child. It is possible to rule out the presence of non-ketotic hyperglycinemia in children by measuring spinal fluid amino acids. In our experience with the three cases described spinal fluid glycine levels were excessively elevated, often to a level at least ten times that of the upper limit of normal. We now use this as a means of assisting in the diagnosis of non-ketotic hyperglycinemia in such children [ 21. The patients with non-ketotic hyperglycinemia were all investigated as a collaborative project with Dr T.L. Perry, Dr A.G.F. Davidson and Dr P.M. MacLeod.

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Interpretation of elevated blood glycine levels in children.

49 Clinica Chimica Acta, 63 (1975) 49-54 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands CCA 7217 INTERPRETATION...
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