A C9orf72 DNA repeat expansion can be detected using a CRISPR Arrayed Repeat Detection System (CARDS). Based upon the compositions and methods supporting this platform primary cell cultures and/or blood cell smears can be tested under conventional clinical diagnostic laboratory conditions to diagnose genetically-based diseases having DNA repeat expansions, including but not limited to ALS. dCas9 constructs are also contemplated as having fluorescent proteins bound to any or all stem loop sequences, wherein detection of a plurality of dCas9 constructs having different colored fluorescent proteins can simultaneously detect at least six (6) different gene target loci.

A C9orf72 DNA repeat expansion can be detected using a CRISPR Arrayed Repeat Detection System (CARDS). Based upon the compositions and methods supporting this platform primary cell cultures and/or blood cell smears can be tested under conventional clinical diagnostic laboratory conditions to diagnose genetically-based diseases having DNA repeat expansions, including but not limited to ALS. dCas9 constructs are also contemplated as having fluorescent proteins bound to any or all stem loop sequences, wherein detection of a plurality of dCas9 constructs having different colored fluorescent proteins can simultaneously detect at least six (6) different gene target loci.

The present invention refers to methods for selectively recognizing a base pair in a DNA sequence by a polypeptide, to modified polypeptides which specifically recognize one or more base pairs in a DNA sequence and, to DNA which is modified so that it can be specifically recognized by a polypeptide and to uses of the polypeptide and DNA in specific DNA targeting as well as to methods of modulating expression of target genes in a cell.