Severe Intellectual Disability and Progressive Spastic Paraplegia, also known as ap4 deficiency syndrome, is related to spastic paraplegia 52, autosomal recessive and hereditary spastic paraplegia 35. An important gene associated with Severe Intellectual Disability and Progressive Spastic Paraplegia is AP4B1 (Adaptor Related Protein Complex 4 Subunit Beta 1), and among its related pathways/superpathways are Vesicle-mediated transport and trans-Golgi Network Vesicle Budding. Affiliated tissues include brain, and related phenotypes are hypotonia and microcephaly