Estimated frequency of genetic and nongenetic causes of congenital idiopathic cerebral palsy in west Sweden.

Mathematical analysis of prenatal and perinatal risk factors was performed on the first 681 published cases of idiopathic congenital cerebral palsy (born 1959-1970) in the west Swedish population-based cerebral palsy (CP) study. Analysis indicates that an estimated 40% of etiologically undiagnosed cases of CP in the community (48% of those born at term and 24% of those born prematurely) are genetically caused. These proportions of genetic causation are no less in CP than in idiopathic mental retardation. Genetic causes account for 60% of maturely born hemiplegics, 45% of maturely born spastic diplegics, 32% of premature spastic diplegics and virtually all cases of pure ataxia. About 23% of CP cases in the community have suffered nongenetic brain damage in accordance with the two-stage model. The residue of 37% is characterized by a single risk factor, usually perinatal.