Biomedical subjects
H A Simmonds
Publications and source records attributed to H A Simmonds.
First trimester diagnosis of adenosine deaminase deficiency.
Adenosine deaminase deficiency has been detected in the first trimester by direct analysis of enzyme activity in chorionic villi in a pregnancy at risk. Data for purine nucleoside phosphorylase activity in chorionic villi from healthy controls in the first trimester are also presented and should allow equally rapid diagnosis of this disorder.
Purine metabolites in uraemia.
Explore the source record for details and available documents.
Use of intact erythrocytes in the diagnosis of inherited purine and pyrimidine disorders.
This paper reports the detection of five inherited disorders of purine and one of pyrimidine metabolism using intact red blood cells (RBCs) and compares the findings with those from RBC lysate activity. Two different phosphate levels (1 and 18 mmol L-1 Pi) were used to evaluate endogenous PP-ribose-P levels and their generation by PP-ribose-P synthetase. The importance of this dual approach is demonstrated by the following evidence: (a) Six out of eight patients with no detectable hypoxanthine-guanine phosphoribosyltransferase (HGPRT) RBC lysate activity had up to 25% of normal activity in their intact RBCs. Two Lesch-Nyhan patients showed no detectable activity in intact or lysed RBCs. (b) RBC lysates from two heterozygotes for adenosine deaminase (ADA) deficiency also showed no detectable activity, but up to 60% of normal activity using intact RBCs. (c) The existence of an aberrant enzyme in a kindred with a superactive PP-ribose-P synthetase was evident from the fact that intact RBCs failed to respond normally to phosphate activation, despite normal HGPRT and adenine phosphoribosyltransferase (APRT) RBC lysate activity. (d) Raised endogenous PP-ribose-P levels in intact RBCs were demonstrable only in purine nucleoside phosphorylase (PNP) and HGPRT deficiency; levels were normal in APRT deficiency and hereditary oroticaciduria (OPRT/ODC) deficiency. The results indicate that diagnosis from RBC lysate activity alone may be misleading. Intact RBC studies clearly provide a better indication of the functional capacity of the enzyme in vivo. They also show a closer correlation with the clinical phenotype and allow further insight into the associated biochemical abnormalities in some cases.
Urinary oxalate levels are not affected by dietary purine intake or allopurinol.
We showed previously that ingestion of a non-specific high purine diet by healthy subjects increased not only urinary uric acid levels but urinary oxalate as well. Both increments were reduced significantly during concomitant allopurinol therapy. The present study was undertaken to investigate these findings in more detail under carefully controlled dietary conditions where a single specific purine, guanosine, was used as an additive and several different methods for oxalate determination (GLC, HPLC, isotacophoresis) were compared with the enzymatic method used previously. Results obtained by two direct techniques of oxalate determination showed no significant alteration in oxalate levels during any dietary regime, suggesting that the earlier results derived from problems inherent in the experimental design and methodology employed. The study confirmed that one of the beneficial effects of allopurinol was to reduce dietary purine absorption. The results may thus provide a logical explanation for the reduced incidence of urolithiasis during allopurinol therapy in some idiopathic oxalate stone formers addicted to purine-rich foods and beverages.
Central nervous system dysfunction and erythrocyte guanosine triphosphate depletion in purine nucleoside phosphorylase deficiency.
Developmental retardation was a prominent clinical feature in six infants from three kindreds deficient in the enzyme purine nucleoside phosphorylase (PNP) and was present before development of T cell immunodeficiency. Guanosine triphosphate (GTP) depletion was noted in the erythrocytes of all surviving homozygotes and was of equivalent magnitude to that found in the Lesch-Nyhan syndrome (complete hypoxanthine-guanine phosphoribosyltransferase (HGPRT) deficiency). The similarity between the neurological complications in both disorders indicates that the two major clinical consequences of complete PNP deficiency have differing aetiologies: neurological effects resulting from deficiency of the PNP enzyme products, which are the substrates for HGPRT, leading to functional deficiency of this enzyme. immunodeficiency caused by accumulation of the PNP enzyme substrates, one of which, deoxyguanosine, is toxic to T cells. These studies show the need to consider PNP deficiency (suggested by the finding of hypouricaemia) in patients with neurological dysfunction, as well as in T cell immunodeficiency. They suggest an important role for GTP in normal central nervous system function.
Heterogeneity of biochemical, clinical and immunological parameters in severe combined immunodeficiency due to adenosine deaminase deficiency.
There was considerable heterogeneity of the biochemical, clinical and immunological findings in 12 patients and two fetuses from 16 kindreds affected by severe combined immunodeficiency (SCID) due to a complete deficiency of the enzyme adenosine deaminase (ADA). Despite this heterogeneity a consistent pattern was observed, in which levels of abnormal purine metabolites paralleled the severity of the immunodeficiency. A high level of urinary deoxyadenosine was a universal finding for homozygous ADA deficiency. ATP depletion, in association with raised deoxy-ATP (dATP) levels, was found in the erythrocytes of nine infants with profound cellular and humoral immunodeficiency. There was no erythrocyte ATP depletion in two patients with some residual immunity, who presented later, but adenosine accumulated in their plasma and urine. This finding, together with the presence of some T and normal B-lymphocytes in less severely affected patients, suggests that adenosine is relatively non-toxic. The other results are consistent with the hypothesis that the sequence of deoxyadenosine accumulation, dATP formation and ATP depletion represents the major mechanism of toxicity to the immune system. Low numbers of T lymphocytes and dATP accumulation were also found in the blood of affected fetuses at 18 weeks gestation. Since extreme instability of erythrocyte ADA was demonstrated in some heterozygotes, and heterozygote ADA levels were detected in one infant with SCID, simultaneous immunological and biochemical analysis of fetal blood are important for precise antenatal diagnosis.
2,8-Dihydroxyadenine lithiasis.
2,8-Dihydroxyadenine (2,8-DHA) lithiasis is a form of kidney stone previously mistaken for uric acid because of identical reactivity in non-specific tests used routinely in stone analysis. Unlike uric acid, the stones crush easily and do not react with uricase. The biochemical basis for the defect is a deficiency of the enzyme adenine phosphoribosyltransferase (APRT). A complete deficiency has been reported in 29 patients from 11 countries. The number of stone formers reported in Japan (10 homozygotes, 16 heterozygotes) Austria (3), and Switzerland (2) suggests more efficient diagnosis in those countries. The defective enzyme in heterozygotes in Japan is a kinetic mutant demonstrable in intact not lysed cells. 20% of APRT-deficient subjects have been asymptomatic. An equal number have presented in acute renal failure, three of whom are now on dialysis. Formation of the nephrotoxic 2,8-DHA can be prevented by allopurinol. This underlines the importance of early diagnosis, since such severe renal damage should be avoidable.
Allopurinol in renal failure and the tumour lysis syndrome.
This paper illustrates several important points relating to the use of allopurinol in renal failure, or situations of purine overproduction: It is very easy to give too much allopurinol. Most of the side effects (bone marrow depression, exfoliative dermatitis, etc) are the result of overdosage due to the retention of oxipurinol, an effect exaggerated by thiazide diuretics. Monitoring of plasma oxipurinol levels (ideally less than 100 mumol/l) by high-pressure liquid chromatography is helpful for adjusting dosage in renal failure. Some estimate of the anticipated purine excess is equally vital in deciding dosage during tumour lysis if the risk of urate nephropathy is not to be substituted for the certainty of xanthine nephropathy. In this situation the use of allopurinol may even be questioned. Patients with HGPRT deficiency are exquisitely sensitive to allopurinol, and careful monitoring of the effect on urinary purine levels is essential if xanthine colic is to be avoided.
Superactivity of human phosphoribosyl pyrophosphate synthetase due to altered regulation by nucleotide inhibitors and inorganic phosphate.
Phosphoribosyl pyrophosphate (PPRibP) synthetase activity was studied in cultured fibroblasts and lymphoblasts from a male child (patient 2-A) in whom inherited purine nucleotide and uric acid overproduction are accompanied by neurological deficits. Chromatographed or partially purified preparations of the child's enzyme showed 5-6-fold increased inhibitory constants (I0.5) for the noncompetitive inhibitors GDP and 6-methylthioinosine monophosphate but normal responsiveness to the competitive inhibitors ADP and 2,3-diphosphoglycerate. Activation of the PPRibP synthetase of patient 2-A by Pi was also abnormal with 3-4-fold reduced apparent KD values for Pi. Superactivity of the PPRibP synthetase of this child thus appeared to result from a combination of regulatory defects; selective resistance to noncompetitive inhibitors and increased responsiveness to Pi activation. Selective growth of the patient's fibroblasts in medium containing 6-methylthioinosine confirmed the functional significance of the in vitro inhibitor resistance of the aberrant enzyme. Fibroblasts and lymphoblasts derived from patient 2-A showed increased concentrations and rates of generation of PPRibP as well as increased rates of the pathways of purine base salvage and purine nucleotide synthesis de novo. The magnitudes of these increases in the child's cells exceeded those in cells with catalytically superactive PPRibP synthetases. These alterations as well as the in vitro kinetic abnormalities in the patient 2-A enzyme were expressed to a reduced degree in fibroblasts from the child's affected mother, supporting the proposal that this woman is a heterozygous carrier for X-linked enzyme superactivity.
Use of biological fluids for the rapid diagnosis of potentially lethal inherited disorders of human purine and pyrimidine metabolism.
Inherited purine and pyrimidine disorders may be associated with serious, sometimes life-threatening consequences. Early and accurate diagnosis is essential. Difficulties encountered when using existing high pressure liquid chromatographic (HPLC) methods led to the development of an improved method based on prior fractionation of urine. The advantages are as follows. 1. Production of fingerprints demonstrating altered urinary excretion patterns characteristic of any one of ten different disorders, in 30 minutes. 2. Positive identification and quantification by comparison with established methods (using conventional chromatography, electrophoresis and UV spectrophotometry) in addition to specific retention times and characteristic UV absorbance ratios at two separate wavelengths (245 and 280 nm) by HPLC. 3. Direct analysis of all the purines and pyrimidines normally found in human body fluids as well as identification of abnormal compounds. 4. Short time between successive analyses while maintaining excellent resolution between compounds of interest and column longevity. 5. Improved separation of the different adenine-based compounds encountered in some disorders, plus demonstration of potential interference by dietary or drug metabolites. 6. Applicability to the monitoring of therapy involving a variety of different purine and pyrimidine analogues. Particular attention should be paid to sample preparation. Plasma profiles will confirm the diagnosis in some, but not all, of these disorders.
Hereditary orotic aciduria: further biochemistry.
Explore the source record for details and available documents.
Correlations between purine levels, clinical and immunological status in ADA deficiency.
Explore the source record for details and available documents.
Usefulness of intact erythrocyte studies in the diagnosis of inherited purine and pyrimidine defects.
Explore the source record for details and available documents.
Source and fate of circulating pyrimidines.
Explore the source record for details and available documents.
The use and abuse of allopurinol in renal failure, the tumour lysis syndrome and HGPRT deficiency.
Explore the source record for details and available documents.
Erythrocyte GTP depletion in PNP deficiency presenting with haemolytic anaemia and hypouricaemia.
Explore the source record for details and available documents.
B-lymphocytes, thymocytes and platelets accumulate high dATP levels in simulated ADA deficiency.
Explore the source record for details and available documents.