Whole genome sequencing of mutation-negative individuals with Cornelia de Lange Syndrome

AimsThis study assesses the diagnostic utility of whole genome sequence analysis in a well-characterised research cohort of individuals referred with a clinical suspicion of Cornelia de Lange syndrome (CdLS) in whom prior genetic testing had not identified a causative variant. MethodsShort read, whole genome sequencing was performed in 195 individuals from 105 families, 108 of whom were affected. 100/108 of the affected individuals had prior relevant genetic testing with no pathogenic variant being identified. The study group comprised 42 trios (affected individuals with both unaffected parents), 61 singletons (unrelated affected individuals) and two families with more than one affected individual. Results32/105 (30.5%) unrelated probands had likely causative coding region disrupting variants. 4 loci were identified in >1 proband; NIPBL (10), ANKRD11 (6), EP300 (3), EHMT1 (2). Single alleles were detected in the remaining genes (EBF3, KMT2A, MED13L, NLGN3, NR2F1, PHIP, PUF60, SET, SETD5, SMC1A, TBL1XR1). Possibly causative variants in non-coding regions of NIPBL were identified in four individuals. Single de novo variants were identified in five genes not previously reported to be associated with any developmental disorder: ARID3A, PIK3C3, MCM7, MIS18BP1 and WDR18. ConclusionsClustering of de novo non-coding variants implicate a single uORF and a small region in intron 21 in NIPBL regulation. Causative variants in genes encoding chromatin-associated proteins, with no defined influence on cohesin function, appear to result in CdLS-like clinical features.