Abstract
BackgroundWe aimed to define the clinical and variant spectrum and to provide novel molecular insights into the DHX30-associated neurodevelopmental disorder.MethodsClinical and genetic data from affected individuals were collected through Facebook-based family support group, GeneMatcher, and our network of collaborators. We investigated the impact of novel missense variants with respect to ATPase and helicase activity, stress granule (SG) formation, global translation, and their effect on embryonic development in zebrafish. SG formation was additionally analyzed in CRISPR/Cas9-mediated DHX30-deficient HEK293T and zebrafish models, along with in vivo behavioral assays.ResultsWe identified 25 previously unreported individuals, ten of whom carry novel variants, two of which are recurrent, and provide evidence of gonadal mosaicism in one family. All 19 individuals harboring heterozygous missense variants within helicase core motifs (HCMs) have global developmental delay, intellectual disability, severe speech impairment, and gait abnormalities. These variants impair the ATPase and helicase activity of DHX30, trigger SG formation, interfere with global translation, and cause developmental defects in a zebrafish model. Notably, 4 individuals harboring heterozygous variants resulting either in haploinsufficiency or truncated proteins presented with a milder clinical course, similar to an individual harboring a de novo mosaic HCM missense variant. Functionally, we established DHX30 as an ATP-dependent RNA helicase and as an evolutionary conserved factor in SG assembly. Based on the clinical course, the variant location, and type we establish two distinct clinical subtypes. DHX30 loss-of-function variants cause a milder phenotype whereas a severe phenotype is caused by HCM missense variants that, in addition to the loss of ATPase and helicase activity, lead to a detrimental gain-of-function with respect to SG formation. Behavioral characterization of dhx30-deficient zebrafish revealed altered sleep-wake activity and social interaction, partially resembling the human phenotype.ConclusionsOur study highlights the usefulness of social media to define novel Mendelian disorders and exemplifies how functional analyses accompanied by clinical and genetic findings can define clinically distinct subtypes for ultra-rare disorders. Such approaches require close interdisciplinary collaboration between families/legal representatives of the affected individuals, clinicians, molecular genetics diagnostic laboratories, and research laboratories.
Highlights
We aimed to define the clinical and variant spectrum and to provide novel molecular insights into the DHX30-associated neurodevelopmental disorder
DHX30 loss-of-function variants cause a milder phenotype whereas a severe phenotype is caused by helicase core motifs (HCMs) missense variants that, in addition to the loss of ATPase and helicase activity, lead to a detrimental gain-of-function with respect to stress granule (SG) formation
These include a winged helix (WH), a ratchet-like (RL) and an we identified four individuals bearing likely pathogenic loss-of-function variants
Summary
We aimed to define the clinical and variant spectrum and to provide novel molecular insights into the DHX30-associated neurodevelopmental disorder. The large helicase superfamily 2 (SF2) contains more than 50 members in humans [3] These are designated DDX and DHX proteins based on the consensus amino acid sequence DExD or DExH signature in their ATP-binding motif II (Walker B motif) [3]. All SF2 RNA helicases are built around a highly conserved helicase core region consisting of two domains that resemble the bacterial recombination protein recombinase A (referred to as RecA-1 and RecA-2) Within these two core helicase domains, eight highly conserved sequence elements, helicase core motifs (HCMs) play a role in either RNA binding, or ATP binding and hydrolysis. The importance and functional relevance of certain SF2 RHs in human neurodevelopment is demonstrated by the identification of pathogenic germline variants in DDX3X [6], DDX6 [7], DHX30 [8], and DDX5 [9] in individuals with neurodevelopmental disorders. A paralog-based study implicated a role for DHX16, DHX34, DHX37, and DDX54, in human neurodevelopmental disorders and suggested that DHX8, DDX47, and DHX58 may be neurodevelopmental genes [10]
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