An extremely rare and complex form of hereditary spastic paraplegia (see this term), reported in only 4 patients from 2 families to date, characterized by spastic paraplegia (presenting between the ages of 1 to 4 years with abnormal gait) associated with microcephaly, amyotrophy, cerebellar signs (e.g. dysarthria) aggressiveness, delayed puberty and mild to moderate intellectual disability. SPG64 is due to mutations in the ENTPD1 gene (10q24.1), encoding ectonucleoside triphosphate diphosphohydrolase 1.