Copy number analysis of NIPBL in a cohort of 510 patients reveals rare copy number variants and a mosaic deletion

Defects of cohesin loader lead to bone dysplasia associated with transcriptional disturbance

Cohesin loader nipped-B-like protein (Nipbl) is increasingly recognized for its important role in development and cancer. Cornelia de Lange Syndrome (CdLS), mostly caused by heterozygous mutations of Nipbl, is an autosomal dominant disease characterized by multiorgan malformations. However, the regulatory role and underlying mechanism of Nipbl in skeletal development remain largely elusive. In this study, we constructed a Nipbl-a Cas9-knockout (KO) zebrafish, which displayed severe retardation of global growth and skeletal development. Deficiency of Nipbl remarkably compromised cell growth and survival, and osteogenic differentiation of mammalian osteoblast precursors. Furthermore, Nipbl depletion impaired the cell cycle process, and caused DNA damage accumulation and cellular senescence. In addition, nucleolar fibrillarin expression, global rRNA biogenesis, and protein translation were defective in the Nipbl-depleted osteoblast precursors. Interestingly, an integrated stress response inhibitor (ISRIB), partially rescued Nipbl depletion-induced cellular defects in proliferation and apoptosis, osteogenesis, and nucleolar function. Simultaneously, we performed transcriptome analysis of Nipbl deficiency on human neural crest cells and mouse embryonic fibroblasts in combination with Nipbl ChIP-Seq. We found that Nipbl deficiency caused thousands of differentially expressed genes including some important genes in bone and cartilage development. In conclusion, Nipbl deficiency compromised skeleton development through impairing osteoblast precursor cell proliferation and survival, and osteogenic differentiation, and also disturbing the expression of some osteogenesis-regulatory genes. Our study elucidated that Nipbl played a pivotal role in skeleton development, and supported the fact that treatment of ISRIB may provide an early intervention strategy to alleviate the bone dysplasia of CdLS.

Efficient detection of copy-number variations using exome data: Batch- and sex-based analyses

Many algorithms to detect copy number variations (CNVs) using exome sequencing (ES) data have been reported and evaluated on their sensitivity and specificity, reproducibility, and precision. However, operational optimization of such algorithms for a better performance has not been fully addressed. ES of 1199 samples including 763 patients with different disease profiles was performed. ES data were analyzed to detect CNVs by both the eXome Hidden Markov Model (XHMM) and modified Nord's method. To efficiently detect rare CNVs, we aimed to decrease sequencing biases by analyzing, at the same time, the data of all unrelated samples sequenced in the same flow cell as a batch, and to eliminate sex effects of X-linked CNVs by analyzing female and male sequences separately. We also applied several filtering steps for more efficient CNV selection. The average number of CNVs detected in one sample was <5. This optimization together with targeted CNV analysis by Nord's method identified pathogenic/likely pathogenic CNVs in 34 patients (4.5%, 34/763). In particular, among 142 patients with epilepsy, the current protocol detected clinically relevant CNVs in 19 (13.4%) patients, whereas the previous protocol identified them in only 14 (9.9%) patients. Thus, this batch-based XHMM analysis efficiently selected rare pathogenic CNVs in genetic diseases.

Comprehensive genetic analysis of 57 families with clinically suspected Cornelia de Lange syndrome

Cornelia de Lange syndrome (CdLS) is a rare multisystem disorder with specific dysmorphic features. Pathogenic genetic variants encoding cohesion complex subunits and interacting proteins (e.g., NIPBL, SMC1A, SMC3, HDAC8, and RAD21) are the major causes of CdLS. However, there are many clinically diagnosed cases of CdLS without pathogenic variants in these genes. To identify further genetic causes of CdLS, we performed whole-exome sequencing in 57 CdLS families, systematically evaluating both single nucleotides variants (SNVs) and copy number variations (CNVs). We identified pathogenic genetic changes in 36 out of 57 (63.2 %) families, including 32 SNVs and four CNVs. Two known CdLS genes, NIPBL and SMC1A, were mutated in 23 and two cases, respectively. Among the remaining 32 individuals, four genes (ANKRD11, EP300, KMT2A, and SETD5) each harbored a pathogenic variant in a single individual. These variants are known to be involved in CdLS-like. Furthermore, pathogenic CNVs were detected in NIPBL, MED13L, and EHMT1, along with pathogenic SNVs in ZMYND11, MED13L, and PHIP. These three latter genes were involved in diseases other than CdLS and CdLS-like. Systematic clinical evaluation of all patients using a recently proposed clinical scoring system showed that ZMYND11, MED13L, and PHIP abnormality may cause CdLS or CdLS-like.

Insights into genetics, human biology and disease gleaned from family based genomic studies

Identifying genes and variants contributing to rare disease phenotypes and Mendelian conditions informs biology and medicine, yet potential phenotypic consequences for variation of >75% of the ~20,000 annotated genes in the human genome are lacking. Technical advances to assess rare variation genome-wide, particularly exome sequencing (ES), enabled establishment in the United States of the National Institutes of Health (NIH)-supported Centers for Mendelian Genomics (CMGs) and have facilitated collaborative studies resulting in novel "disease gene" discoveries. Pedigree-based genomic studies and rare variant analyses in families with suspected Mendelian conditions have led to the elucidation of hundreds of novel disease genes and highlighted the impact of de novo mutational events, somatic variation underlying nononcologic traits, incompletely penetrant alleles, phenotypes with high locus heterogeneity, and multilocus pathogenic variation. Herein, we highlight CMG collaborative discoveries that have contributed to understanding both rare and common diseases and discuss opportunities for future discovery in single-locus Mendelian disorder genomics. Phenotypic annotation of all human genes; development of bioinformatic tools and analytic methods; exploration of non-Mendelian modes of inheritance including reduced penetrance, multilocus variation, and oligogenic inheritance; construction of allelic series at a locus; enhanced data sharing worldwide; and integration with clinical genomics are explored. Realizing the full contribution of rare disease research to functional annotation of the human genome, and further illuminating human biology and health, will lay the foundation for the Precision Medicine Initiative.

NIPBL expression levels in CdLS probands as a predictor of mutation type and phenotypic severity

Cornelia de Lange syndrome (CdLS) is a rare, genetically heterogeneous multisystem developmental disorder with a high degree of variability in its clinical presentation. Approximately 65% of probands harbor mutations in genes that encode core components (SMC1A, SMC3, and RAD21) or regulators (NIPBL, HDAC8) of the cohesin complex, of which mutations in NIPBL are the most common. Cohesin plays a canonical role in sister chromatid cohesion during cell division and non-canonical roles in DNA repair, stem cell maintenance and differentiation, and regulation of gene expression. Disruption of the latter role seems to be the major contributor to the underlying molecular pathogenesis of CdLS. NIPBL is required for loading and unloading the cohesin complex onto chromosomes. The expression levels of NIPBL itself appear to be tightly regulated and highly evolutionarily conserved. Droplet digital PCR was used to quantify NIPBL mRNA expression levels with high precision from a cohort of 37 samples (NIPBL, SMC1A, SMC3, and HDAC8 mutation positive probands and negative control). Probands with severe forms of CdLS or severe mutation types were found to have lower levels of NIPBL in comparison to phenotypically milder patients and controls. Levels of NIPBL also correlated with the presence of mutations in different CdLS-causing genes. The data suggests that NIPBL levels are closely correlated with the severity of CdLS and with specific causative genes and types of mutations. ddPCR may provide a tool to assist in diagnostic approaches to CdLS, for genetic counseling and prognosis, and for monitoring potential therapeutic modalities in the future. © 2016 Wiley Periodicals, Inc.

Neuroimaging features of Cornelia de Lange syndrome

BACKGROUND

Cornelia de Lange syndrome is a rare genetic disease characterized by distinctive facial dysmorphia and dwarfism. Multiple organ system involvement is typical. Various central nervous system (CNS) aberrations have been described in the pathology literature; however, the spectrum of neuroimaging manifestations is less well documented.

OBJECTIVE

To present neuroimaging findings from a series of eight patients with Cornelia de Lange syndrome.

MATERIALS AND METHODS

The CT/MR database at a single academic children's hospital was searched for the terms "Cornelia," "Brachmann" and "de Lange." The search yielded 18 exams from 16 patients. Two non-CNS and six exams without available images were excluded. Ten exams from eight patients were evaluated by a board-certified neuroradiologist.

RESULTS

All patients had skull base dysplasia, most with an unusual coronal basioccipital cleft (7/8). All brain MR exams showed microcephaly, volume loss and gyral simplification (5/5). Six patients had an absent massa intermedia. Four patients had small globe anterior segments; three had optic pathway hypoplasia. Basilar artery fenestration was present in two patients; vertebrobasilar hypoplasia was present in one patient. The inner ear vestibules were dysplastic in two patients. One patient had pachymeningeal thickening. Spinal anomalies included scoliosis, segmentation anomalies, endplate irregularities, basilar invagination, foramen magnum stenosis and tethered spinal cord.

CONCLUSION

Typical imaging manifestations of Cornelia de Lange syndrome include skull base dysplasia with coronal clival cleft, cerebral and brainstem volume loss, and gyral simplification. Membranous labyrinth dysplasia, anterior segment and optic pathway hypoplasia, basilar artery fenestration, absent massa intermedia and spinal anomalies may also be present.

Global transcriptional disturbances underlie Cornelia de Lange syndrome and related phenotypes

Cornelia de Lange syndrome (CdLS) is a genetically heterogeneous disorder that presents with extensive phenotypic variability, including facial dysmorphism, developmental delay/intellectual disability (DD/ID), abnormal extremities, and hirsutism. About 65% of patients harbor mutations in genes that encode subunits or regulators of the cohesin complex, including NIPBL, SMC1A, SMC3, RAD21, and HDAC8. Wiedemann-Steiner syndrome (WDSTS), which shares CdLS phenotypic features, is caused by mutations in lysine-specific methyltransferase 2A (KMT2A). Here, we performed whole-exome sequencing (WES) of 2 male siblings clinically diagnosed with WDSTS; this revealed a hemizygous, missense mutation in SMC1A that was predicted to be deleterious. Extensive clinical evaluation and WES of 32 Turkish patients clinically diagnosed with CdLS revealed the presence of a de novo heterozygous nonsense KMT2A mutation in 1 patient without characteristic WDSTS features. We also identified de novo heterozygous mutations in SMC3 or SMC1A that affected RNA splicing in 2 independent patients with combined CdLS and WDSTS features. Furthermore, in families from 2 separate world populations segregating an autosomal-recessive disorder with CdLS-like features, we identified homozygous mutations in TAF6, which encodes a core transcriptional regulatory pathway component. Together, our data, along with recent transcriptome studies, suggest that CdLS and related phenotypes may be "transcriptomopathies" rather than cohesinopathies.