Structural and functional birth defects

What are Structural Birth Defects and Functional Birth Defects?

Birth defects are either structural or functional abnormalities. Structural birth defects include abnormalities in the development of body parts including the skeleton and organs. Functional birth defects are abnormalities in the systems that run the body like the neurological, immune and endocrine systems. Major structural abnormalities may be identified at birth, but functional abnormalities can take months or years to identify.

Structural Birth Defects

Structural birth defects are abnormalities in the structure of body parts. Examples of structural birth defects include cleft palate, heart defects, club foot, missing or abnormal limbs, etc. Most structural defects develop in the earliest weeks of pregnancy when all of the organs and the skeleton are forming. The most common structural birth defects are heart defects.

Causes of Structural Birth Defects

Structural birth defects can be part of a genetic syndrome (about 20%) or they can be caused by environmental factors during conception and pregnancy. These factors can include maternal illnesses (ex. Diabetes or toxoplasmosis); viruses (rubella and CMV); alcohol and/or smoking; nutritional deficiencies (lack of folic acid); exposures to teratogens (ex. medications, radiation, chemicals, heavy metals.) Most structural birth defects, however, are multi-factorial. This means that a genetic predisposition for a birth defect is triggered by an adverse factor or exposure in the maternal or paternal prenatal or pre-conceptual history. (For more on birth defect causes and prevention, visit our Healthy Baby Resource.)

Functional Birth Defects

Functional birth defects are problems in how a body system works. This can lead to developmental disabilities which can include:

  • Nervous system and brain problems including learning disabilities; intellectual impairment, behavioral disorders, seizures, speech and language disabilities, ASDs (autistic spectrum disorders) and attention disorders.
  • Sensory disorders including blindness and other visual problems along with deafness and partial hearing loss.
  • Metabolic disorders can involve problems with processes that help the body break down certain substances leading to a buildup of harmful toxins. An example is PKU (phenyhlkentonuria) where the body can’t break down the amino acid phenylalanine. Other metabolic problems include dysfunction of endocrine glands like the thyroid leading to hyper or hypothyroidism.
  • Degenerative disorders where the child seems to be developing normally but suddenly starts to lose function and previously acquired skills. Some examples are Rett Syndrome, muscular dystrophy and X-ALD (the subject of the movie Lorenzo’s Oil).
  • Immune disorders, a newly explored area, in which the child’s immune system does not function adequately to protect them from constant infections, allergic disorders, asthma, autoimmune diseases and/or cancer. 

What Causes Functional Birth Defects?

Some functional disorders like X-ALD are caused by genetic mutations. Others like PKU are inherited conditions. There are also functional defects that have been linked to environmental exposures in the maternal and/or paternal pre-conceptual or prenatal history. As with structural birth defects, there is likely a genetic predisposition that is triggered by an environmental exposure in these cases. (For more on birth defect causes and prevention, visit our Healthy Baby Resource.)


Birth Defect Research for Children, Inc.
(Formerly Association of Birth Defect Children)
976 Lake Baldwin Drive, Suite 104
Orlando, FL 32814
Phone: (407) 895-0802


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