AP4S1 and Spastic paraplegia: This condition is part of a group known as adaptor protein complex 4-associated hereditary spastic paraplegias (AP-4 HSP), which includes four subtypes: spastic paraplegia 47 (SPG47), spastic paraplegia 50 (SPG50), spastic paraplegia 51 (SPG51), and spastic paraplegia 52 (SPG52), each caused by single-gene mutations in the Adaptor-Related Protein Complex 4 Subunit β 1 (AP4B1)*, Adaptor-Related Protein Complex 4 Subunit Mu 1(AP4M1)*, Adaptor-Related Protein Complex 4 Subunit Epsilon 1 (AP4E1)*, and Adaptor-Related Protein Complex 4 Subunit Sigma 1 (AP4S1)* genes, respectively [3,4,5,6,7].