Identification and Detection of the Common 65-kb Deletion Breakpoint in the Nephropathic Cystinosis Gene (CTNS)

The most common mutation in the cystinosis gene, CTNS, is a 65-kb deletion thought to have originated in Germany. Although homozygotes for this deletion are detectable by the absence of the D17S829 polymorphic marker, no method exists to identify heterozygotes. We identified the 65-kb deletion breakpoints and used flanking PCR primers to amplify a 423-bp fragment present only in the deletion alleles. Using this method, we determined that 121 of 216 (56%) cystinosis alleles examined bore the 65-kb deletion. We found no non-Europeans with the deletion, and the deletion size and breakpoints appeared identical in all patients studied, supporting the concept of a founder effect. The addition of D17S829 primers (266 bp apart) to the PCR created a multiplex PCR system useful for diagnosing cystinosis patients homozygous and heterozygous for the 65-kb deletion.