Large Genomic Mutations within the ATM Gene Detected by MLPA, Including a Duplication of 41 kb from Exon 4 to 20

Summary Mutation detection remains problematic for large genes, primarily because PCR‐based methodology fails to detect heterozygous deletions and any duplication. In the ATM gene only a handful of multi‐exon deletions have been described to date, and this type of mutation has been considered rare. To address this issue we tested a new MLPA (Multiplex Ligation Probe Amplification) kit that covers 33 of the 66 ATM exons, using for controls two previously characterized genomic deletions in addition to three A‐T patients, taken from a survey of nine, who had missing four mutations unidentified after conventional mutation screening. We identified for the first time: 1) a ∼41 kb genomic duplication spanning exons 4–20 (c.‐30_2816dup41kb)(a.k.a., ATM dup 41 kb); 2) a novel genomic deletion including exon 31, and 3) in hemizygosis a point mutation in the non‐deleted exon 31. In this study we extended mutation detection to nine new Italian A‐T patients, using a combined approach of haplotype analysis, DHPLC and MLPA. Overall we achieved a mutation detection rate of >97%, and can now define a spectrum of ATM mutations based on twenty‐one consecutive Italian families with A‐T.