Heterozygous variants disrupting the interaction of ERF with activated ERK1/2 cause microcephaly, developmental delay, and skeletal anomalies.

Heterozygous deleterious null alleles and specific missense variants in the DNA-binding domain of the ETS2 repressor factor (ERF) cause craniosynostosis, while the recurrent p.(Tyr89Cys) missense variant is associated with Chitayat syndrome. Exome and whole transcriptome sequencing revealed the ERF de novo in-frame indel c.911_913del selectively removing the serine of the FSF motif, which interacts with the extracellular signal-regulated kinases (ERKs), in a 10-year-old girl with microcephaly, multiple congenital joint dislocations, generalized joint hypermobility, and Pierre-Robin sequence. Three additional cases with developmental delay variably associated with microcephaly, Pierre-Robin sequence and minor skeletal anomalies were detected carrying heterozygous de novo non-truncating alleles (two with c.911_913del and one with the missense c.907 T > A change) in the same FSF motif. Protein affinity maps, co-immunoprecipitation experiments and subcellular distribution showed that both the variants impair the interaction between ERF and activated ERK1/2 and increase ERF nuclear localization, affecting ERF repressor activity that may lead to developmental defects. Our work expands the phenotypic spectrum of ERF-related disorders to a pleiotropic condition with microcephaly, developmental delay and skeletal anomalies, that we termed MIDES syndrome, and adds to the understanding of the relevance of the ERF-ERK interaction in human development and disease.