In humans, dominant gain-of-function DIAPH1 variants cause sensorineural deafness and macrothrombocytopenia (DFNA1), while homozygous DIAPH1 loss leads to seizures, cortical blindness, and microcephaly syndrome (SCBMS). Here, DIAPH1 is linked to progressive microcephaly-seizures-cortical blindness-developmental delay syndrome.