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Eur J Med Genet. 2018 Nov;61(11):680-684. doi: 10.1016/j.ejmg.2017.11.004. Epub 2017 Nov 15.

Novel mosaic variants in two patients with Cornelia de Lange syndrome.

Author information

1
Section for Functional Genetics, Institute of Human Genetics, Lübeck, Germany.
2
Ambulantes Gesundheitszentrum Humangenetik, Charité Universitätsmedizin Berlin, Berlin, Germany.
3
Faculté de Médecine, Institut de Génétique et Développement de Rennes, Rennes, France.
4
Department of Cell Biology, Erasmus MC, Rotterdam, The Netherlands.
5
Division of Experimental Paediatric Endocrinology and Diabetes, Department of Paediatrics and Adolescent Medicine, University of Lübeck, Lübeck, Germany.
6
Institute of Human Genetics, Technische Universität München, Munich, Germany; Institute of Human Genetics, Helmholtz Zentrum München, Munich, Germany.
7
Institute of Human Genetics, Lübeck, Germany.
8
Section for Functional Genetics, Institute of Human Genetics, Lübeck, Germany. Electronic address: frank.kaiser@uksh.de.

Abstract

Cornelia de Lange syndrome (CdLS) is a dominantly inherited developmental disorder caused by mutations in genes that encode for either structural (SMC1A, SMC3, RAD21) or regulatory (NIPBL, HDAC8) subunits of the cohesin complex. NIPBL represents the major gene of the syndrome and heterozygous mutations can be identified in more than 65% of patients. Interestingly, large portions of these variants were described as somatic mosaicism and often escape standard molecular diagnostics using lymphocyte DNA. Here we discuss the role of somatic mosaicism in CdLS and describe two additional patients with NIPBL mosaicism detected by targeted gene panel or exome sequencing. In order to verify the next generation sequencing data, Sanger sequencing or pyrosequencing on DNA extracted from different tissues were applied. None of the pathogenic variants was originally detected by Sanger sequencing on blood DNA. Patient 1 displays an unusual combination of clinical features: he is cognitively only mildly affected, but shows severe limb reduction defects. Patient 2 presents with a moderate phenotype. Interestingly, Sanger sequencing analysis on fibroblast DNA of this patient did not detect the disease-causing variant previously observed on the same DNA sample by exome sequencing. Subsequent analyses could confirm the variants by Sanger sequencing on buccal mucosa DNA. Notably, this is the first report of a higher mutational load in buccal mucosa than in fibroblast cells of a CdLS patient. Detection of low-level mosaicism is of utmost importance for an accurate molecular diagnosis and a proper genetic counseling of patients with a clinical diagnosis of CdLS. Next-generation sequencing technologies greatly facilitate the detection of low-level mosaicism, which might otherwise remain undetected by conventional sequencing approaches.

KEYWORDS:

Cornelia de Lange syndrome; Mosaicism; NIPBL

PMID:
29155047
DOI:
10.1016/j.ejmg.2017.11.004

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