Biallelic loss-of-function variants of ZFTRAF1 cause neurodevelopmental disorder with microcephaly and hypotonia

Purpose: Neurodevelopmental disorders exhibit clinical and genetic heterogeneity, ergo manifest dysfunction in components of diverse cellular pathways; the precise pathomechanism for the majority remains elusive. Methods: We studied 5 affected individuals from 3 unrelated families manifesting global developmental delay, postnatal microcephaly, and hypotonia. We used exome sequencing and prioritized variants that were subsequently characterized using immunofluorescence, immunoblotting, pulldown assays, and RNA sequencing. Results: We identified biallelic variants in ZFTRAF1, encoding a protein of yet unknown function. Four affected individuals from 2 unrelated families segregated 2 homozygous frameshift variants in ZFTRAF1, whereas, in the third family, an intronic splice site variant was detected. We investigated ZFTRAF1 at the cellular level and signified it as a nucleocytoplasmic protein in different human cell lines. ZFTRAF1 was completely absent in the fibroblasts of 2 affected individuals. We also identified 110 interacting proteins enriched in mRNA processing and autophagy-related pathways. Based on profiling of autophagy markers, patient-derived fibroblasts show irregularities in the protein degradation process. Conclusion: Thus, our findings suggest that biallelic variants of ZFTRAF1 cause a severe neurodevelopmental disorder.