Lesch-Nyhan syndrome fibroblasts

It is noteworthy that for the Lesch-Nyhan syndrome fibroblasts, the assay in the presence of TTP furnished the bulk of the radioactivity in the nucleoside fraction rather than in the nucleotide fraction, in contrast to normal cell extracts in which the bulk of the radioactivity is found in the nucleotide fraction. Two possible explanations may be entertained to explain this observation. First, in the HGPRT-deficient system the nucleotidase activity is far in excess over the HGPRT activity, and presumably the residual nucleotidase activity, not inhibited by TTP, is sufficient to degrade the relatively small amount of nucleotide formed. Secondly, the possibility should be considered that the accumulation of radioactivity in the nucleoside fraction reflects the anabolic activity of nucleoside phospho-rylase reacting the purine base with ribose-l-phosphate to form the nucleotide by an alternative pathway. However, this latter explanation seems to be invalid in view of the absence of the suitable substrate, ribose-l-phosphate, from the incubation system, and by the linearity... 

Activities of HGPRT and APRT in cultured skin fibroblasts from the normal, a male patient with Lesch-Nyhan syndrome, heterozygous females, the proband and her mother were shown in Table 2. Like the male patient, the girl showed a virtually complete deficiency of HGPRT activity. The activities of two heterozygotes were about one half of the activity of normal individuals. The patient s mother had apparently normal level of HGPRT activity. 

An almost complete deficiency of the enzyme hypoxanthine guanine phosphoribosyl transferase (HPRT) is known to be the cause of the Lesch-Nyhan syndrome (1,2) The gene for HPRT is located on the X-chromosome, so that heterozygous females show two populations of cells, one HPRT and one HPRT ", as predicted by the hypothesis of Lyon (3,4). Such mosaicism has been demonstrated in populations of cultured fibroblasts and in hair root follicles of heterozygotes (4,5). 

Increased intracellular levels of PP-ribose-P have been implicated in the cause of certain hyperuricemic states associated with uric acid overproduction. Fibroblasts from two patients with the Lesch-Nyhan syndrome were found previously to have an elevated intracellular concentration of PP-ribose-P with a normal rate of PP-ribose-P production (Rosenbloom, et al., 1968). Green and Seegmiller (1969) subsequently reported a mean PP-ribose-P value of 47.1 in erythrocytes from seven patients with HGPRT deficiency. We have confirmed these elevated PP-ribose-P levels in three additional patients with the Lesch-Nyhan syndrome with values of 20.5, 39.4 and 49.5 juM (Table 1). The mothers of these patients are obligate heterozygotes and have normal PP-ribose-P levels. Two diseases associated with a deficiency of other PRT enzymes are not associated with altered erythrocyte PP-ribose-P levels (Table 1). PP-ribose-P levels were in the normal range in one patient with a partial deficiency of adenine phosphoribosyltransferase (APRT) and in one patient with orotic aciduria, which is due to a deficiency... 

Kelley, W. N. and Meade, J. C. 1971. Studies on hypoxanthine-guanine phosphoribosyltransferase in fibroblasts from patients with the Lesch-Nyhan syndrome. Evidence for genetic heterogeneity. 

Table 1 shows HGPRT activity in fresh hemolysate from 5 patients with the Lesch-Nyhan syndrome and from 119 normal individuals. Hemolysates from 9 other patients with the Lesch-Nyhan syndrome which had been stored at -20 prior to assay showed no detectable HGPRT activity. Several other investigators have also noted low levels of HGPRT activity in erythrocytes (Mizuno, et al., 1970 Sorensen, 1970) and this finding is consistent with the low but readily detectable levels of HGPRT activity found in cultured fibroblasts from patients with the Lesch-Nyhan syndrome (Kelley and Meade, 1971). 

The deficiency of hypoxanthine guanine-phosphoribosyltrans-ferase (HGPRT) activity of patients with the Lesch-Nyhan syndrome is accompanied by an accelerated rate of purine biosynthesis de novo. This elevated rate of purine biosynthesis is reflected in fibroblasts cultured from the skin of these patients and is accompanied by elevated levels of phosphoribosylpyrophosphate (PRPP). 

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