Processed Pseudogene Confounding Deletion/Duplication Assays for SMAD4

Mutations in SMAD4 have been associated with juvenile polyposis syndrome and combined juvenile polyposis/hereditary hemorrhagic telangiectasia syndrome. SMAD4 is part of the SMAD gene family. To date, there has been no report in the literature of a SMAD4 pseudogene. An unusual SMAD4 duplication pattern was seen in multiple patient samples using two different duplication/deletion platforms: multiplex ligation–dependent probe amplification and chromosomal microarray. Follow-up confirmatory testing included real-time quantitative PCR and sequencing of an exon/exon junction, all results leading to the conclusion of the existence of a processed pseudogene. Examination of clinical results from two laboratories found a frequency of 0.26% (12 in 4672 cases) for this processed pseudogene. This is the first report of the presence of a processed pseudogene for SMAD4 . We believe that knowledge of its existence is important for accurate interpretation of clinical diagnostic test results and for new assay designs. This study also indicates how a processed pseudogene may confound quantitative results, dependent on placement of probes and/or primers in a particular assay design, potentially leading to both false-positive and false-negative results. We also found that the SMAD4 processed pseudogene affects next-generation sequencing results by confounding the alignment of the sequences, resulting in erroneous variant calls. We recommend Sanger sequencing confirmation for SMAD4 variants.