[A study on effects of parents age, birth order and mental retardation of unknown etiology].

On this report 461 matched cases of mental retardation of unknown aetiology were analysed on the relationship between the diseases and the parents age, birth orders with conditional Logistic regression. These cases were accurately diagnosed and selected from the Epidemiologic Survey of genetic diseases of Sichuan, China. The results found that mental retardation of unknown aetiology is related to the age of parents and birth order. The paternal age is the main factor while the maternal age in not a significant effect and birth order also in not a significant effect after readjusting the other factors. Compared to paternal age group of under 25. There are significant increase of relative risks of age group 30-34 and 45 above, about 1.8 and 2.7 fold increase in univariate analysis and 1.9 and 3.3 fold increase in controlling the maternal age and birth order, a chi-square test for trend of distribution of paternal age also indicates a significant dose response relationship between increasing risk with age. The significance of result and methods of analysis were discussed.