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 five affected individuals from three unrelated families manifesting global developmental delay, postnatal microcephaly, and hypotonia. We employed 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 two unrelated families segregated two 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 two 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.