Birth defects are the leading cause of infant mortality in the United States, resulting in more than 8,000 infant deaths each year. In addition, another 40,000 babies are born and live with congenital disorders that result in a variety of disabilities ranging from treatable anomalies to life-long challenges. These include spina bifida, hydrocephalus, cerebral palsy, heart defects, and clefts of the lip and palate. Although the causes of 75 percent of all birth defects remain unknown, some congenital disorders can be prevented. Congenital Disorders Sourcebook offers current information about congenital disorders related to the effects of toxic substances, disease organisms, birth trauma, spontaneous malformations, and other disorders of unknown origin. (Information on disorders with a known genetic basis is included in Genetic Disorders Sourcebook.)