Global Study Examines Toll of Genetic Defects
Tuesday, January 31, 2006
About 6 percent of children worldwide -- nearly 8 million babies a year -- are born with a physical or mental disability caused by a genetic defect, according to the first comprehensive estimate of the global toll.
Each year, about 3.3 million of them die before their fifth birthday, victims of what the report's authors call a "serious and vastly unappreciated public health problem."
Although parents everywhere face some risk of having a child with a defect, the risk is much greater in poor and middle-income countries. Reasons include inadequate maternal health and prenatal care, more intermarriage, and a higher frequency of some disease-causing genes.
The experience in rich countries over the past quarter-century, however, suggests that 70 percent of these defects can be prevented or lessened.
The authors of the report, which was sponsored by the March of Dimes, hope it will be the first step in convincing countries that birth defects are neither inevitable nor untreatable.
"We hope researchers and others will go to their health ministries and say, 'Here are the data; we have a problem,' " said Christopher P. Howson, an epidemiologist at the March of Dimes.
Interventions proven to work include genetic counseling for sickle cell anemia, prenatal diagnosis of Down syndrome, supplementing folic acid in the diet to reduce the risk of neural tube defects, newborn screening for some rare metabolic disorders such as phenylketonuria, and surgical repair of heart defects. Most of those strategies are unavailable in low-income countries.
"Birth defects are a really still pond," Howson said. "We hope this report will be like a rock dropped into that pond that creates changes in policy and action."
The data come from many sources.
Industrialized countries have registries that compile statistics on birth defects, but many lower-income countries do not. For them, the authors used data from research studies, statistics from neighboring countries, and estimates based on known facts, such as the prevalence of the sickle cell genetic mutation in a population.
There are about 7,000 known defects caused by genetic errors. The researchers estimated that in 2001, about one-quarter of the defects were of five common types -- heart malformations, defects of the neural tube that develops into the brain and spinal cord, disorders of hemoglobin, the oxygen-carrying protein in blood, Down syndrome, and an enzyme disorder called G6PD deficiency.
The 85-page report does not include defects caused by damage to the fetus during pregnancy, primarily from exposure to alcohol, iodine deficiency in the mother, rubella (German measles) infection and syphilis. Those statistics are even harder to obtain.