Lysosomal cystine counter-transport in heterozygotes for cystinosis.

Heterozygotes for cystinosis exhibited approximately half the normal rate of cystine counter-transport into isolated leukocyte lysosomes. This gene-dosage effect strongly supports previous findings demonstrating that the basic defect in cystinosis is impaired cystine transport across the lysosomal membrane. The method was used to determine the cystinosis carrier status for siblings of affected children in two families with cystinosis.