The Problem of Birth Defects: Causes Unknown

the problem with birth defects

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Look up in our Glossary

chromosome
exposure
gene
mutation
heart defect
neural tube defect
oral cleft
risk factor
teratogen

Despite recent advances in genetic research, we cannot pinpoint the causes of most birth defects. Evidence suggests the need for careful study to untangle the complex interplay of factors involved.

	Some birth defects—fewer than 10%—-result from known prenatal exposures. German measles, diabetes or heavy drinking during pregnancy are all examples of teratogens, exposures that can cause birth defects.

	Others are due to abnormal genes or chromosomes. These may be inherited or represent new mutations.

	Most birth defects—including common conditions like neural tube and heart defects—arise from interactions between genes and non-genetic factors. For instance, we discovered that smoking increases risk for oral clefts, particularly in babies who inherit a specific gene variant.

WHY ARE BIRTH DEFECTS SO HARD TO STUDY?

	Research findings in animals often don't apply to humans.

	Despite the progress of the Human Genome Project, we don't understand the purpose and function of most genes.

	Exposures during pregnancy are difficult to identify and document. Multiple risk factors may be present.

	Many common, everyday exposures have not been well studied. Environmental issues—like air and water pollution—are sources of particular public concern.

Finding birth defects causes depends on rigorous study of gene-environment interactions in humans—the main focus of the California Birth Defects Monitoring Program.

Sonia did everything right. While pregnant, she followed her doctor's instructions, didn't use alcohol or drugs, ate nutritious meals and exercised regularly—long walks around the commercial flower fields near her San Diego home.

When Sonia's son was born with a life-threatening heart defect, the daily walks haunted her. Had pesticides sprayed over the fields harmed her developing child? Medical science did not have the answer. The causes of her child's heart abnormality—like the majority of birth defects—are not well understood. Most potential environmental exposures, including pesticides, were not well-studied in human pregnancy.

Sonia's story—a composite of many—is not unusual...1 in every 33 babies is born with birth defects. Many are fatal or will cause lifelong handicap—children who may never see, hear or walk. And yet, the causes of birth defects remain largely a mystery.