AbstractThe Lesch‐Nyhan syndrome results as a consequence of a severe deficiency of functional activity of purine salvage enzyme, hypoxanthine phosphoribosyltransferase (HPRT). We performed Southern blot analysis for five patients and their families using full length cDNA of the HPRT gene as a probe.PstI digested Southern blot analysis revealed a large deletion that included exon 2 in patient 3. The size of this deletion was about 4.4 Kb. The mother of this patient had the same mutated allele and a normal one (heterozygote). This type of mutation from a Lesch‐Nyhan syndrome patient has not been previously reported. The restriction fragment length polymorphism (RFLP) pattern was analyzed byBamHI digested Southern blot analysis for one family who had no major gene abnormality. We determined from this analysis that the sister of the patient was a Lesch‐Nyhan syndrome carrier and the fetus (brother) was normal for HPRT activity. This study shows RFLP analysis is still useful for carrier detection and prenatal diagnosis of Lesch‐Nyhan s