PDCD6IP and microcephaly: While overlapping, a more severe neurological phenotype involving seizures, microcephaly, progressive spasticity, brain atrophy, and hypomyelination of white matter appears to be associated with PTPN23 missense variants located within the BRO1-like [16], tyrosine–protein phosphatase [15], and ALIX domains [17,18] (Table S1, Figure S4).