The Purine Requirement of Cells Cultured From Humans Affected With the Lesch-Nyhan Syndrome (Hypoxanthine-Guanine Phosphoribosyltransferase Deficiency)

Abstract

Abstract.-Humans with the Lesch-Nyhan syndrome have an X-chromosomal mutant gene that causes severe neurological and developmental abnormalities. The patients are deficient in hypoxanthine-guanine phosphoribosyltransferase, which converts hypoxanthine to inosinic acid, a major precursor of adenine and guanine nucleotides. Paradoxically, the enzyme defect causes hypernormal de novo synthesis of inosinic acid, which manifests itself as excesses of hypoxanthine, xanthine, and uric acid. The first step in the de novo pathway is thought to be rate-limiting, due to feedback repression by adenine and guanine nucleotides. The derepressed rate of purine production in mutants and their failure to thrive could result from reduction in the amounts of nucleotides derived from inosinic acid to levels that are inadequate for normal feedback control and for nucleic acid synthesis needed in growth. Studies Introduction.-The enzyme hypoxanthine-guanine phosphoribosyltransferase (E.C. 2.4.2.81) carries out the reaction:

No evidence that skewing of X chromosome inactivation patterns is transmitted to offspring in humans

“…Skewed patterns of XCI were initially found in female carriers of specific X-linked mutations (8,9) where skewing resulted from the negative selection of cells harboring the lethal allele in the active state. Skewing of XCI was also reported in rare cases of balanced X/autosome translocations, which perturbed the normal mechanisms of XCI (10).…”

Adenine and Folic Acid in the Lesch-Nyhan Syndrome

“…Administered in subsequent studies to two maternal cousins of the twins who had clinical features of the L-N syndrome and absence of erythrocyte hypoxanthine-guanine phosphoribosyltransferase activity were adenine, 10 mg/kg/24 hr, adenine, 40 mg/kg/24 hr, folic acid, and monosodium glutamate. Low dose adenine had a slight suppressive effect on glycine-1- 14 C incorporation into uric acid; high dose adenine had a strong suppressive effect in the second patient. We conclude that the adenine dose chosen for therapy was too low.…”

“…[29] demonstrated that control of hyperuricemia with allopurinol begun in the neonatal period in an effected patient did not alter the development of the L-N syndrome. We knew that adenine and folic acid enabled fibroblasts to grow in limiting media [14] and that adenine has renal toxicity in rats [34]. It was then decided to treat both twins with folic acid and twin A with adenine to test the hypothesis that one or both of these materials, started at birth, would affect development of central nervous system dysfunction.…”

“…A 70-g protein diet, essentially free of j:>urines, was started 1 week before glycine radiochemical injection and continued for the duration of the study. In a control study, 2 /xCi/kg glycine-l- 14 C was injected intravenously and uric acid- 14 C was isolated from the urine by repeated precipitation after addition of cold carrier [46]. Isolated uric acid was solubilized in Hyamine, added to Scintisol, and radioactivity was determined with a Packard liquid scintillation counter [56].…”

“…However, this approach may not be elected in some patients, and it was not possible in our situation, in which fetal cells with a mutant enzyme were identified late in pregnancy. Some evidence was available in 1968 to suggest that it was possible to affect abnormalities of cells with mutant H-G PRT in culture with adenine and folic acid [14]. The enzyme defect of the L-N syndrome was confirmed in identical twin males by H-G PRT assay of cord blood hemolysates.…”