tokens: In two patients ( DTD and AO2 / DTD ) , no other structural mutation was found , but polymerase chain reaction amplification and single - strand conformation polymorphism analysis of fibroblast cDNA showed reduced mRNA levels of the wild - type DTDST allele these two patients may be compound heterozygotes for the " Finnish " mutation ( as yet uncharacterized at the DNA level ) , which causes reduced expression of DTDST .