Purine synthesis de novo and salvage in Lesch-Nyhan syndrome patients‘ tissues

Abstract

The Lesch-Nyhan syndrome is a rare inborn error of metabolism due to hypoxanthine phosphoribosyltransferase (HPRT; EC 2.4.2.8) deficiency. The patients have neurological and behavioural abnormalities with hypotonia, torsion dystonia, compulsive self-injury, dysarthria and in some cases megaloblastic anaemia, as well as the results of excessive uric acid production (gout and uric acid urinary stones) and growth delay. Prepubertal testicular atrophy and a partial failure of the 1 lphydroxylation of steroids are recently described additional facets of the disease (Watts et a/., 1987). There are no primary structural or ultrastructural alterations except in the testis and sometimes.in the bone marrow. The availability of purine ribonucleotidcs in specific tissues depends on local synthesis de tiovo and on the purine phosphoribosyltransferase-catalysed pyrophosphorylation of the free purine bases (purine salvage) as well as on purines transported in erythrocytes from other biosynthetic sites (Murray, 1971). It has been suggested that the brain, testis and bone marrow are particularly dependent on the purine salvage pathway and that this explains the neurological manifestations, testicular atrophy and megaloblastic anaemia. The rate of purine synthesis de novo in the patients as a whole is accelerated (Seegmiller et al., 1967). This implies increased synthesis de tiovo at the tissue level. However, there has been no direct evidence as to whether this could involve the organs and tissues generally or only some of them. The present communication reports measurements of the activity of the purine synthesis pathway de novo in tissues from two patients with the Lesch-Nyhan syndrome, together with the activities of the purine phosphoribosyltransferase enzymes [HPRT and adenine phosphoribosyltransferase (APRT; EC 2.4.2.7)] in the same tissues. Table 1 shows the results of the purine synthesis de novo activity measurements. This pathway was active in all the tissues studied. As anticipated, there was no HPRT activity (assayed as described by Craft et al., 1970). APRT activity (assayed as described by Dean et al., 1968) was present. The presence of purine synthesis de novo agrees with the previous report that amidophosphoribosyltransferase (EC 2.4.2.14), the first enzyme of the pathway, was present in the tissues of another Lesch-Nyhan syndrome patient (Watts et al., 1982). For clinical reasons, the tissues from the two patients could only be obtained 6 and 10 h after death, respectively. Control experiments with rat tissue showed that the purine synthesis activity de novo had decreased by about 30-50% of the time zero value by 12 h after death, whereas the HPRT and APRT activities were approximately constant over this time period. Therefore, the relative activities of the two pathways cannot bc compared directly. However, these results establish the presence of purine synthesis activity de novo directly in the Lesch-Nyhan syndrome patients’ tissues generally. HPRT catalyses the pyrophosphorylation of