AP4B1 and Intellectual disability: Children with SPG47 present with progressive spastic paraplegia, global developmental delay and later intellectual disability, secondary microcephaly, early-onset epilepsy and cerebral dysgenesis including thinning of the corpus callosum (Ebrahimi-Fakhari et al, 2020; Ebrahimi-Fakhari et al, 2021a; Jordan et al, 2021).