Menkes X linked disease: two clonal cell populations in heterozygotes.

The 64Cu incorporation into fibroblast clones obtained from three obligate and three suspected Menkes disease heterozygotes was studied. For each obligate heterozygote, two clonal cell populations were observed, one with a Menkes phenotype and one with a normal phenotype, as predicted by the Lyon hypothesis. The cloning results suggested a heterozygous state in two of the suspected carriers. The theoretical and practical limitation of the cloning method for identification of carriers of X linked diseases are discussed.