Phenotypic variability in glutaric aciduria type I: Report of fourteen cases in five Canadian Indian kindreds. We describe 14 patients with glutaric aciduria type 1 in five Canadian Indian kindreds living in Manitoba and northwest Ontario. The patients had marked clinical variability of the disease, even within families. Eight followed the typical clinical course of normal early growth and development until the onset of neurologic abnormalities, often precipitated by infection, between 6 weeks and 7 1/2 months of age. Five patients had early developmental delay; one was thought to be normal until 8 years of age. Three patients died, seven are severely mentally and physically handicapped, and four have only mild mental retardation or incoordination. Six patients had macrocephaly in the neonatal period. Computed tomography was done for 12 patients, and findings were abnormal in 11. Glutaric acid and 3-hydroxyglutaric acid were detected in increased amounts in the urine of all patients, but the concentrations were much lower than those in most other reported patients. Glutaryl coenzyme A dehydrogenase activity in skin fibroblasts, interleukin-2-dependent lymphocytes, or both, ranged from 0% to 13% of control values. There was no correlation between clinical severity and urine glutaric acid concentration or level of residual enzyme activity. We recommend that organic acid analysis of the urine be done in patients with unexplained cerebral palsy-like disorders, especially if the computed tomographic scan is abnormal. If there is suspicion of glutaric aciduria, glutaryl-coenzyme A dehydrogenase should be measured in fibroblasts or lymphocytes even if glutaric acid is not increased in the urine. 