Genotype–phenotype correlations and novel molecular insights into the DHX30-associated neurodevelopmental disorders
Authors: Mannucci Ilaria , Dang Nghi D. P. , Huber Hannes , Murry Jaclyn B. , Abramson Jeff , Althoff Thorsten , Banka Siddharth , Baynam Gareth , Bearden David , Beleza-Meireles Ana , Benke Paul J. , Berland Siren , Bierhals Tatjana , Bilan Frederic , Bindoff Laurence A. , Braathen Geir Julius , Busk Øyvind L. , Chenbhanich Jirat , Denecke Jonas , Escobar Luis F. , Estes Caroline , Fleischer Julie , Groepper Daniel , Haaxma Charlotte A. , Hempel Maja , Holler-Managan Yolanda , Houge Gunnar , Jackson Adam , Kellogg Laura , Keren Boris , Kiraly-Borri Catherine , Kraus Cornelia , Kubisch Christian , Le Guyader Gwenael , Ljungblad Ulf W. , Brenman Leslie Manace , Martinez-Agosto Julian A. , Might Matthew , Miller David T. , Minks Kelly Q. , Moghaddam Billur , Nava Caroline , Nelson Stanley F. , Parant John M. , Prescott Trine , Rajabi Farrah , Randrianaivo Hanitra , Reiter Simone F. , Schuurs-Hoeijmakers Janneke , Shieh Perry B. , Slavotinek Anne , Smithson Sarah , Stegmann Alexander P. A. , Tomczak Kinga , Tveten Kristian , Wang Jun , Whitlock Jordan H. , Zweier Christiane , McWalter Kirsty , Juusola Jane , Quintero-Rivera Fabiola , Fischer Utz , Yeo Nan Cher , Kreienkamp Hans-Jürgen , Lessel Davor 
Published: May 2021

Abstract
Background
We aimed to define the clinical and variant spectrum and to provide novel molecular insights into the DHX30-associated neurodevelopmental disorder.

Methods
Clinical 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.

Results
We 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.

Conclusions
Our 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.