HYPOXANTHINE-GUANINE PHOSPHORIBOSYLTRANSFERASE (HPRT) DEFICIENCY - IDENTIFICATION OF POINT MUTATIONS IN JAPANESE PATIENTS WITH LESCH-NYHAN SYNDROME AND HEREDITARY GOUT AND THEIR PERMANENT EXPRESSION IN AN HPRT-DEFICIENT MOUSE-CELL LINE

Two different single nucleotide transitions of hypoxanthine-guanine ph osphoribosyltransferase (HPRT) were identified in a Japanese patient w ith Lesch-Nyhan syndrome (LNS) and a patient with hereditary gout. HPR T enzyme activities in the two patients were severely deficient, but t he size and amount of mRNA were normal according to Northern analysis. Entire coding regions of HPRT cDNAs were amplified by PCR and sequenc ed. A G-to-A substitution at base 208 in exon 3, which predicted glyci ne 70 to arginine, was detected in the LNS patient (identical mutation with HRPT(Utrecht)). A C-to-A substitution at base 73 in exon 2, whic h predicted proline 25 to threonine, was detected in the gout patient (designated HPRT(Yonago)). We transfected normal HPRT cDNA, mutant cDN A with HRPT(Utrecht) or mutant cDNA with HRPT(Yonago)respectively, to HPRT-deficient mouse cells and isolated permanent expression cell line s. The HPRT-deficient mouse cells had no detectable HPRT activity and a very low amount of HPRT mRNA. When the HPRT-deficient mouse cells we re transfected with normal human cDNA, HPRT enzyme activity increased to 21.8% that of normal mouse cells. The mouse cells transfected with HPRT(Utrecht) showed no increase in HPRT activity; however, when the m ouse cells were transfected with HPRT(Yonago), the activity increased to 2.4% that of normal activity. The proliferative phenotypes of these cells in HAT medium and in medium containing 6-thioguanine were simil ar to those of skin fibroblasts from the patients. This series of stud ies confirmed that each of the two point mutations was responsible for the decreases in HPRT enzyme activity, and the proliferative phenotyp es in HAT medium and medium containing 6-thioguanine.