Fig. 11. The ornithine tolerance test, indicating plasma ornithine levels after an oral loading dose of 100 mg/kg l-ornithine. Note the clear segregation of homozygous patients. The heterozygous parents and controls show less complete segregation from each other. (Modified from Takki D, Simell O: Genetic aspects in gyrate atrophy of the choroid and retina with hyperornithinemia. Br J Ophthalmol 58:907, 1974.)