A 13 base pair deletion in exon 1 of HPRTIllinois forms a functional GUG initiation codon.

More than 50 mutations in the human hypoxanthine-guanine phosphoribosyltransferase (HPRT) locus have been described, yet only 2 alter the AUG initiation codon. One, variant HPRT1151, results in Lesch-Nyhan syndrome (LNS), and the other, HPRTIllinois, results in partial HPRT deficiency. Although previously undetectable, we used a sensitive gel assay to demonstrate that HPRTIllinois is not only active, but has a native Mr indistinguishable from normal.