Heterozygous variants in FBXW7 have recently been recognized as a cause of a rare neurodevelopmental disorder with variable developmental delay, neurological manifestations, and multisystem involvement. The breadth of clinical variability and penetrance remains incompletely defined. We report a retrospective multicenter case series of seven previously unreported individuals (five males, two females) with heterozygous FBXW7 variants identified through clinical genetic testing, aged 5–9 years at last evaluation (median 6 years). Six variants occurred de novo and one was inherited. Neurodevelopmental involvement was present in six individuals and was characterized by global developmental delay and language impairment; hypotonia was observed in all seven. Formal intellectual disability was documented in four cases, while one individual showed preserved cognitive functioning with predominant behavioral difficulties. Epileptic seizures occurred in four individuals, whereas three had no history of epilepsy. Brain MRI was available for six individuals and was normal in four, whereas two showed structural anomalies involving the corpus callosum. Extracerebral features were variably reported, most commonly constipation and recurrent respiratory/otolaryngological infections. Comparison with previously reported individuals confirmed the core neurodevelopmental phenotype and further refined the spectrum. This case series expands the phenotypic spectrum associated with FBXW7-related neurodevelopmental disorder and highlights variable expressivity and incomplete penetrance, including clinically relevant variants presenting with mild or atypical phenotypes. These findings support considering FBXW7 across a broad range of neurodevelopmental presentations and inform genetic counseling.
Salvatore Savasta, F. Comisi, G. Dell’Isola et al.· Journal of Neurodevelopmenta...· 0 citations
Variants in BRSK2, encoding brain specific kinase-2, have recently been associated with an autosomal dominant neurodevelopmental disorder (NDD). We have assembled 52 cases with heterozygous BRSK2 variants and variable neurodevelopmental phenotypes with frequent neuropsychiatric and behavioral symptoms. The variant spectrum included 15 different truncating variants, seven (potential) splice variants, three structural variants, and 12 different missense variants. Of the missense variants, seven were in the kinase domain, and the others in the UBA and the KA1 domain or outside domains. Variants occurred de novo in 19 cases and were inherited in 18. We utilized Drosophila melanogaster as a model and assessed viability and performed climbing and bang sensitivity assays upon knockdown of the fly orthologue sff or upon overexpression of wildtype or mutant human BRSK2. Pan-neuronal knockdown of sff resulted in impaired locomotor behavior and seizure susceptibility. Ubiquitous or pan-neuronal overexpression of human wildtype BRSK2 in Drosophila resulted in lethality or locomotor impairment, respectively, indicating toxicity. Overexpressing mutant BRSK2 did not or incompletely affect viability and locomotor behavior for six of seven tested kinase domain missense variants and one KA1 domain variant, indicating a (partial) loss-of-function effect. Interestingly, overexpressing BRSK2 with the remaining missense variant from the kinase domain and the two most C-terminal missense variants resulted in possible gain of function. Our findings further delineate the clinical and molecular spectrum of BRSK2-associated NDD and provide further insights into the role of BRSK2/sff in nervous system function and dysfunction.
Palak Singhal, Tzung-Chien Hsieh, Nadja Ehmke et al.· European Journal of Human Ge...· 0 citations