A method of screening a subject for susceptibility to functional-ATM protein deficiency, wherein the screening comprises determining the presence of a nonthymine variant residue rs609261 located at position -3 relative to the 3 splice site of a non-sense mediated RNA decay switch exon NSE (cryptic exon in ATM intron 28) of the human genome, wherein the presence of a non-thymine variant residue rs609261 indicates that the subject has, or is susceptible to, functional-ATM protein deficiency. In some embodiments, also included herein are compositions and methods of modulating protein expression that uses an agent that targets a transposed element, methods of treatment and kits for detection of the mutation.
