a method for isolating nucleic acid molecules having a repeating nucleotide sequence or a homopolymeric nucleotide sequence , e . g . a poly a stretch , is described . in particular , the method uses oligomeric capture probes spiked with various amounts of locked nucleic acid . the invention further describes methods for the isolation of rna molecules , for example polyadenylated mrna molecules , which overcome the problems of rapid rna degradation during isolation and analysis of such nucleic acid molecules . this is of major clinical and diagnostic importance , especially when dealing with rna viruses , such as retroviruses or when analyzing rare or low - abundant mrnas or mrnas from biopsies or tissues enriched with rnases .