De Novo Variants in RAB11B Cause Various Degrees of Global Developmental Delay and Intellectual Disability in Children.

BACKGROUND: RAB11B was described previously once with a severe form of intellectual disability. We aim at validation and delineation of the role of RAB11B in neurodevelopmental disorders. METHODS: We present seven novel individuals with disease-associated variants in RAB11B when compared with the six cases described in the literature. We performed a cross-sectional analysis to identify the clinical spectrum and the core phenotype. Additionally, structural effects of the variants were assessed by molecular modeling. RESULTS: Seven distinct de novo missense variants were identified, three of them recurrent (p.(Gly21Arg), p.(Val22Met), and p.(Ala68Thr)). Molecular modeling suggests that those variants either affect the nucleotide binding (at amino acid positions 21, 22, 33, 68) or the interaction with effector molecules (at positions 72 and 75). Our data confirmed the main manifestations as neurodevelopmental disorder with intellectual disability (85%), muscular hypotonia (83%), structural brain anomalies (77%), and visual impairment (70%). Combined analysis indicates a genotype-phenotype correlation; variants impacting the nucleotide binding cause a severe phenotype with intellectual disability, and variants outside the binding pocket lead to a milder phenotype with epilepsy. CONCLUSIONS: We confirm that disease-associated missense variants in RAB11B cause a neurodevelopmental disorder and suggest a genotype-phenotype correlation based on the impact on nucleotide binding functionality of RAB11B.

Routine Diagnostics Confirm Novel Neurodevelopmental Disorders.

Routine diagnostics is biased towards genes and variants with satisfactory evidence, but rare disorders with only little confirmation of their pathogenicity might be missed. Many of these genes can, however, be considered relevant, although they may have less evidence because they lack OMIM entries or comprise only a small number of publicly available variants from one or a few studies. Here, we present 89 individuals harbouring variants in 77 genes for which only a small amount of public evidence on their clinical significance is available but which we still found to be relevant enough to be reported in routine diagnostics. For 21 genes, we present case reports that confirm the lack or provisionality of OMIM associations (ATP6V0A1, CNTN2, GABRD, NCKAP1, RHEB, TCF7L2), broaden the phenotypic spectrum (CC2D1A, KCTD17, YAP1) or substantially strengthen the confirmation of genes with limited evidence in the medical literature (ADARB1, AP2M1, BCKDK, BCORL1, CARS2, FBXO38, GABRB1, KAT8, PRKD1, RAB11B, RUSC2, ZNF142). Routine diagnostics can provide valuable information on disease associations and support for genes without requiring tremendous research efforts. Thus, our results validate and delineate gene-disorder associations with the aim of motivating clinicians and scientists in diagnostic departments to provide additional evidence via publicly available databases or by publishing short case reports.

Endocannabinoid dysfunction in neurological disease: neuro-ocular DAGLA-related syndrome.

The endocannabinoid system is a highly conserved and ubiquitous signalling pathway with broad-ranging effects. Despite critical pathway functions, gene variants have not previously been conclusively linked to human disease. We identified nine children from eight families with heterozygous, de novo truncating variants in the last exon of DAGLA with a neuro-ocular phenotype characterized by developmental delay, ataxia and complex oculomotor abnormality. All children displayed paroxysms of nystagmus or eye deviation accompanied by compensatory head posture and worsened incoordination most frequently after waking. RNA sequencing showed clear expression of the truncated transcript and no differences were found between mutant and wild-type DAGLA activity. Immunofluorescence staining of patient-derived fibroblasts and HEK cells expressing the mutant protein showed distinct perinuclear aggregation not detected in control samples. This report establishes truncating variants in the last DAGLA exon as the cause of a unique paediatric syndrome. Because enzymatic activity was preserved, the observed mislocalization of the truncated protein may account for the observed phenotype. Potential mechanisms include DAGLA haploinsufficiency at the plasma membrane or dominant negative effect. To our knowledge, this is the first report directly linking an endocannabinoid system component with human genetic disease and sets the stage for potential future therapeutic avenues.