Biological functions such as cell proliferation, movement and death processes are also linked to these networks through the genes Camk2a, Cryab, Egr1, Gstm1, Itpr1, Mbp, Nrgn, Ppp1r1b, Ppp3ca, Rgs4, Sept4, Sirpa and Sncb. Known human neurological disorders associated with Network 3 include Pelizaeus-Merzbacher disease ([OMIM:312080]; PLP1) and dementia with Lewy bodies ([OMIM:127750]; SNCB), whereas X-linked mental retardation ([OMIM:300210]; TSPAN7 or TM4SF2) is associated with network 4. The gene discussed is PLP1; the disease is Pelizeaus-Merzbacher spectrum disorder.