tokens: We examined galactosylceramidase ( GALC ) cDNA in four Japanese patients with adult onset globoid cell leukodystrophy ( Krabbe disease ; AO - GLD ) by polymerase chain reaction / single - strand conformation polymorphism ( PCR - SSCP ) analysis , subsequent sequence determination , and restriction enzyme digestion of PCR products , initial symptoms were the onset of slowly progressive spastic paraplegia from the middle of the second decade , and all patients had diminished GALC activity in their leukocytes .