NIPA2 and fragile X syndrome: Each of the four evolutionarily conserved genes that escape imprinting and contiguously lie within the BP1-BP2 region are associated with distinct cardinal diseases: NIPA1: Spastic Paraplegia 6, Autosomal Dominant and Spastic Paraplegia 6; NIPA2: Angelman Syndrome and Prader–Willi Syndrome; CYFIP1: Fragile X Syndrome and Autism; and TUBGCP5: Prader–Willi Syndrome (see Table 15).