[Cerebral palsy--investigation of its causal factors and genetical background].

In the last 30 years the prevalence rate of cerebral palsy (CP) has remarkably decreased in Japan. The decrease is arbitrarily attributed to the reduced frequency of such risk factors for CP, as low birthweight, severe asphyxia, and kernicterus in the neonatal period. However, there is no statistical data providing the evidence that CP patients complicating these risk factors have actually decreased so far. In order to make clear the bases of the decrease in prevalence of CP, we examined the changing patterns in the suggested cause of CP, experienced in the last 30 years. The investigation included the maternal condition of pregnancy and delivery, in relation to the neonatal risk factors, and genetic background of the family. In CP, low birthweight babies of 2500 gm or less were common (36.9%) and the mean birthweight (2689 gm) was obviously smaller than that of general population. In spite of the constant decline of the incidence of low birthweight babies in the general population in the last 30 years, the ratio of low birthweight to total births in CP group had not changed in this study period. It was concluded that the low birthweight following premature birth is still an important predisposing factor of CP. Asphyxia was frequently seen in the CP population. The rate of asphyxia was significantly higher in the group with a normal birthweight more than 2501 gm (58.4%), or gestational weeks longer than 36 weeks (57.7%), comparing with that of low birthweight (41.1%), or premature (40.7%) group.(ABSTRACT TRUNCATED AT 250 WORDS)