Pediatric Genetics: 5 Types of Birth Defects
Pediatric geneticists are physicians who provide medical care to children of all ages from birth through adolescence. They use their extensive training in medicine, pediatrics and genetics to diagnose and treat the roughly 120,000 babies born each year in the US with a defect that affects their health and requires treatment.
Today, all newborns are screened shortly after birth for a variety of medical conditions that can be detected by established tests. These tests are conducted on all infants regardless of whether or not they appear healthy, since many defects are not visible at birth. Not all newborn screenings involve genetically based conditions, but if the tests reveal a genetic issue, the family and infant will be referred to a pediatric geneticist.
About 20% of birth defects are related to genetic or hereditary influences, 10% are caused by environmental factors such as conditions within the womb that affect the baby’s development, and 70% are unknown, representing a complex relationship between genetics, environment and other causes.
While newborn screenings help identify many genetic conditions, by age one an estimated 20% of babies are identified as having birth defects, because the condition was present but could not be detected at birth.
Birth defects are categorized in a variety of ways, but common classifications include:
- Hereditary conditions. This is the broadest classification, and it includes disorders that are passed down in families. Examples vary widely and include everything from hemophilia to specific types of heart, kidney, structural, chemical and metabolic disorders.
- Chromosome abnormalities. Chromosomes contain the genetic code that makes each of us who we are. Defects or mutations in one or more chromosomes occur for a variety of reasons and cause physical and developmental issues that range from mild to severe. Down syndrome, which is caused by the presence of an extra chromosome, is perhaps the most familiar genetic disorder related to a chromosome abnormality.
- Single gene defects. This classification describes specific disorders that are caused by a single gene, a circumstance that is relatively rare. Some conditions are caused by a single defective gene inherited from one parent, while others require the presence of two genes with the same defect (one from each parent). Cystic fibrosis, Fragile X syndrome, Huntington disease, muscular dystrophy and sickle cell disease are examples of single gene diseases.
- Multifactorial conditions. This category represents traits or disorders caused by a combination of genetic and environmental factors. Height is a good example: While height is generally determined by genes inherited from the parents, it’s also related to external factors such as nutrition. The genetic component means multifactorial disorders can run in families, and examples include hip dysplasia or neural tube defects such as spinal bifida and anencephaly.
- Teratogens. This classification encompasses a wide array of external or environmental factors that may cause birth defects. Because the developing fetus shares the mother’s blood supply, anything circulating in her bloodstream has the potential to affect the baby’s development. Environmental factors range from prescribed medications and medical treatments to recreational drugs, alcohol consumption and diseases such as infections.
This article is not intended as medical advice. See your pediatrician for specific advice on your child’s health.