Recently we identified by whole-exome sequencing the homozygous missense variant [NM_004577.4: c.398A > G p.(Asn133Ser)] in the human PSP encoding gene in two siblings with a neurodevelopmental syndrome, a myelopathy (spastic paraplegia) and a low L-Ser plasma level compared to healthy controls. The gene discussed is PSPH; the disease is Myelopathy.