An enumerative assay of purine analogue resistant lymphocytes in women heterozygous for the Lesch-Nyhan mutation

Abstract

In females heterozygous for the Lesch-Nyhan (LN) mutation, there is mosaicism of peripheral blood lymphocytes (PBLs) with regard to sensitivity to 6-thioguanine (TG) inhibition of tritiated thymidine ([³H]Tdr) incorporation following phytohemagglutinin (PHA) stimulation. That there are two populations of PBLs, normal and mutant (LN-like), has been demonstrated by an autoradiographic enumerative assay. A single three-generation family containing six potentially heterozygous females was studied. Five of the six were mosaics with frequencies of TG-resistant (TG^r) PBLs ranging from 1.4×10⁻³ to 4.2×10⁻³ when tested at 2×10⁻⁴ m TG. The median frequency of TG^r PBLs in 63 healthy non-LN individuals between the ages of 11 and 75 years was found to be 1.1×10⁻⁴ (mean 1.3×10⁻⁴) (10th and 90th percentiles—6.1×10⁻⁵ and 2.1×10⁻⁴) and was not age related. The sixth potentially heterozygous female in the current family had a TG^r PBL frequency of 1.9×10⁻⁴. In the five females with elevated TG^r PBL frequencies, TG^r skin fibroblasts with frequencies ranging from 26% to 100% of the sample tested were found; in the female with the normal TG^r PBL frequency, no TG^r skin fibroblasts were found. The former group was considered to be LN heterozygous. Four of the five had been previously diagnosed as such. The latter individual is considered to be genotypically normal. Females who are heterozygotes for the LN mutation have two populations of PBLs.