Hidden Mutations in Cornelia de Lange Syndrome Limitations of Sanger Sequencing in Molecular Diagnostics

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Cornelia de Lange syndrome (CdLS) is a well-characterized developmental disorder. The genetic cause of CdLS is a mutation in one of five associated genes (NIPBL,SMC1A, SMC3, RAD21, andHDAC8) accounting for about 70% of cases. To improve our current molecular diagnostic and to analyze some of CdLS candidate genes, we developed and established a gene panel approach. Because recent data indicate a high frequency of mosaicNIPBLmutations that were not detected by conventional sequencing approaches of blood DNA, we started to collect buccal mucosa (BM) samples of our patients that were negative for mutations in the known CdLS genes. Here, we report the identification of three mosaicNIPBLmutations by our high-coverage gene panel sequencing approach that were undetected by classical Sanger sequencing analysis of BM DNA. All mutations were confirmed by the use of highly sensitive SNaPshot fragment analysis using DNA from BM, urine, and fibroblast samples. In blood samples, we could not detect the respective mutation. Finally, in fibroblast samples from all three patients, Sanger sequencing could identify all the mutations. Thus, our study highlights the need for highly sensitive technologies in molecular diagnostic of CdLS to improve genetic diagnosis and counseling of patients and their families.

High-coverage gene panel sequencing using buccal mucosa DNA samples of patients with Cornelia de Lange Syndrome could identify de-novo mutations in NIPBL that were not detected by conventional Sanger sequencing approaches. The figure compares the electropherograms of Sanger sequencing analyses on blood, buccal mucosa and fibroblasts DNA samples of all three patients. While none of the mutations was identified in blood and buccal mucosa samples all mutations were detected in DNA of the fibroblast samples.

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