Department of Laboratory Medicine, University of Washington, Seattle, Washington, USA.
Genet Med. 2013 Dec;15(12):1004-7. doi: 10.1038/gim.2013.51. Epub 2013 Apr 25.
Mosaic PTEN mutations are not well described in Cowden syndrome. We report a 40-year-old woman with a clinical diagnosis of Cowden syndrome including Lhermitte-Duclos disease, who had a mosaic PTEN mutation detected by next-generation deep sequencing.
Complete PTEN gene sequencing by the Sanger method and deletion/duplication analysis performed on DNA extracted from blood leukocytes at a commercial clinical laboratory did not identify a mutation. Because of high suspicion of a PTEN mutation, we repeated testing by next-generation sequencing using the ColoSeq assay, which sequences the entire PTEN locus at >320-fold average coverage.
ColoSeq identified a frameshift PTEN mutation (c.767_768delAG) in 1.7% of sequencing reads from peripheral blood leukocytes (21/1,184 reads), which is below the limit of detection of most Sanger sequencing methods. The mutation was detected at full heterozygous levels in skin fibroblasts and a cerebellar tumor, and at approximately the 25% level in colonic and endocervical mucosa, confirming somatic mosaicism.
Our report highlights the power of deep next-generation sequencing to identify mosaic mutations that can be missed by traditional less sensitive approaches. We speculate that mosaic PTEN mutations are more common in Cowden syndrome than previously described.
多发性错构瘤综合征中 PTEN 基因突变并不常见。我们报告了一名 40 岁的女性，临床诊断为多发性错构瘤综合征，包括 Lhermitte-Duclos 病，通过下一代深度测序检测到镶嵌性 PTEN 突变。
通过 Sanger 法对完整的 PTEN 基因进行测序，并在商业临床实验室提取的血液白细胞 DNA 上进行缺失/重复分析，未发现突变。由于高度怀疑存在 PTEN 突变，我们通过 ColoSeq 检测进行了重复检测，该检测以 >320 倍的平均覆盖率对整个 PTEN 基因座进行测序。
ColoSeq 在来自外周血白细胞的测序读数中发现了一个错义 PTEN 突变（c.767_768delAG），在 1.7%的测序读数中（21/1,184 个读数），这低于大多数 Sanger 测序方法的检测极限。该突变在皮肤成纤维细胞和小脑肿瘤中以完全杂合状态检测到，在结肠和宫颈黏膜中以约 25%的水平检测到，证实了体细胞镶嵌性。
我们的报告强调了深度下一代测序在识别传统敏感性较低的方法可能遗漏的镶嵌突变方面的强大功能。我们推测，在多发性错构瘤综合征中，镶嵌性 PTEN 突变比以前描述的更为常见。
