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Common Types of Birth Defects

A birth defect is any physical or mental disabling or fatal abnormality in function, structure or metabolism that is present at birth. To date, medical science has identified thousands of different birth defects, ranging in severity from very minor to life-threatening.

Around 3% of all newborns have some kind of birth defect. Birth defects account for more than 20% of all infant deaths and are thus the most common cause of infant death during the first year of life. Those infants with moderate to severe birth defects who survive have an increased risk of long-term health problems, but proper treatment often allows many of them to lead full, healthy lives. However, some defects cannot be treated.

During pregnancy, a single fertilized egg grows and divides into billions of cells and many different body systems are developed, eventually forming a baby. Any change to any cell, gene or enzyme that affects this incredibly complex process may result in an anomaly. Some anomalies that occur during pregnancy are too severe to be compatible with life and a miscarriage occurs. In other instances, the baby continues to develop but is born with a birth defect.

A birth defect may develop at any stage of pregnancy, though most abnormalities occur during the first three months of pregnancy when organs are formed. Any developmental abnormality that occurs during these early stages of development may cause the fetus to grow defectively for the rest of the pregnancy. Any factor that interferes with the proper formation of the organs can cause a birth defect.

A single factor, such as an extra chromosome or missing or abnormal gene, may be the cause of a birth defect. In other cases, a combination of several factors including maternal age, smoking, alcohol abuse, medications or infections may affect the developing fetus and cause birth defects. However, for most birth defects the cause is not known.

Many birth defects are detected before birth. Those that have not been prenatally detected and are not obvious at birth are usually discovered through newborn screening tests. Although most developmental abnormalities are detected within the first year of infant’s life, some may not be discovered until childhood or even adulthood.

Certain types of birth defects can be corrected through surgery in early infancy while others can be treated through nonsurgical means. However, birth abnormalities that cause mental retardation usually present lifelong challenges to both parents and children. In some cases, birth defects can be treated before birth with injections and sometimes even with prenatal surgery.

Classification of Birth Defects

Scientists have so far identified more than 4,000 different birth defects that can be classified in numerous ways. They vary widely, from structural defects (e.g., heart defects) to functional problems (e.g., deafness, blindness) and metabolic problems, where the body lacks or cannot process certain enzymes. There are also birth defects that may encompass more than just one problem.

In addition, birth defects can be classified by their suspected cause, which may also vary. For instance, many birth defects are genetic disorders caused by a problem in the infant’s genetic structure and may also include structural, functional or metabolic disorders or their combination.

The most common birth defects include:

  • Heart defects. These are the most common structural birth defects. Between 0.5-1.0% of all infants are born with a heart defect. They range in severity from mild to serious and may include holes in the heart or malformed heart chambers or valves. Many heart defects can be effectively treated using surgery or other techniques. These birth defects cause more infant deaths than any other birth abnormality.
  • Genital or urinary defects. Around 0.7% of infants are born with a defect in their genital or urinary system. These birth defects also range from mild to severe. One such example is hypospadias, which may affect male infants and occurs when the urethral opening is formed on the underside of the penis instead of the tip. This birth defect can be repaired surgically.
  • Cerebral palsy. This is a group of disorders that cause brain damage and affect muscle control with varying degrees of impairment. Around 0.3-0.5% of infants are born with cerebral palsy. Mental retardation as well as other disabilities also occur in about 70% of patients with this condition.
  • Clubfoot. This is the incorrect formation of the bones, joints, muscles and blood vessels in the foot and ankle. Clubfoot causes the feet to point down and turn in and limits the range of motion of the feet. It occurs in about 0.1% of infants. Treatment may require casts and surgery.
  • Cleft lip and/or palate (Orofacial clefts). Approximately 0.1% of infants are born with an orofacial cleft. The disorder is more common among Asian, Native American and Hispanic infants. Orofacial clefts can be corrected through surgery.
  • Down syndrome. It is one of the most common genetic disorders. Down syndrome is caused by an extra chromosome and is characterized by mental retardation, abnormal facial features and slow growth. This defect occurs in around 0.1% of infants. Down syndrome is more common in infants born to older mothers.
  • Congenital hip dislocation. It occurs when the round upper end of the thighbone fails to sit properly inside the socket of the pelvis. Dislocation can happen in one or both hips and tends to affect girls more often than boys. This defect is usually detected at birth and is treated by placing the infant in a soft sling for 6-9 months.
  • Congenital hypothyroidism. When an infant’s thyroid gland is underdeveloped or absent at birth the child’s body cannot produce enough thyroid hormone. Thyroid hormone is a substance which supports normal growth and brain development. If not treated early, congenital hypothyroidism can lead to developmental delays and permanent retardation. Hence, in order to prevent this risk, infants are routinely given a blood test shortly after birth to check for this condition.
  • Sickle cell anemia. It is a genetic blood disorder characterized by an abnormal shape of the red blood cells. Sickle cell anemia usually results in chronic anemia, painful attacks and other health problems. Around 0.2% of African American infants and 0.1% of Hispanic infants are born with this condition.
  • Neural tube defects. These are defects in the brain or spinal cord that appear in the first month of pregnancy. Neural tube defects occur in around 0.1% of pregnancies. They most commonly include:
  1. Spina bifida. This most common neural tube defect occurs when the vertebral column fails to close completely, leaving the spinal cord partially exposed. Around 0.5 per mille of infants are born with this defect. Spina bifida can often be corrected surgically. Some children with the condition experience few problems, while others may have some paralysis and other nerve problems.
  2. Anencephaly. It occurs when parts of the brain fail to develop. Infants born with this neural tube defect die at birth or shortly after. Anencephaly affects around 0.3 per mille of infants.
  • Cystic fibrosis. This condition results in thick mucus in the lungs and other organs, causing breathing and other problems. Around 0.6 per mille of Caucasian infants are born with cystic fibrosis. This disease is much less common in African Americans and Hispanics.
  • Fragile X syndrome. Features of this disorder include autistic-like behavior, hyperactivity, attention problems and mental impairment. Fragile X syndrome occurs in around 0.5 per mille of male infants and about half as many female infants.
  • Turner syndrome. This disorder occurs only in females when one of the two X chromosomes is missing or incomplete. Common symptoms of Turner syndrome include short stature and absent or delayed puberty.
  • Triple X Syndrome. This genetic abnormality also only affects females when there is an extra X chromosome in each cell. Features include taller than average height, a small head, poor motor skills, learning disabilities or behavioral problems and infertility. Sometimes it is symptom-free and may never be discovered.
  • Tay-Sachs disease. It is a degenerative metabolic and genetic condition most common in people of European Jewish descent. This condition causes brain damage and often leads to blindness, dementia, seizures and paralysis. Tay-Sachs disease is eventually fatal.
  • Gastrointestinal defects. Birth defects affecting the digestive tract often cause obstructions or blockages and usually require surgical treatment. One example of a gastrointestinal defect is imperforate anus. In this condition, the opening at the end of the digestive tract is missing or closed.

Other genetic birth defects include the most common form of dwarfism called achondroplasia, muscular dystrophy and the bleeding disorder hemophilia. Many genetic disorders involve metabolic abnormalities characterized by an inability to produce, transport or use biological molecules such as certain enzymes or proteins. Approximately 0.3 per mille of infants are born with metabolic abnormalities. An example of a metabolic abnormality is phenylketonuria, in which protein is not properly processed and builds up in the blood and tissue. If left untreated, phenylketonuria leads to mental retardation. Early treatment with a diet low in amino acid phenylalanine can be used to prevent brain damage.

In addition, some birth defects can be defined by their cause, including:

  • Rhesus (Rh) disease of the newborn. This disorder occurs when the mother’s blood is incompatible with the blood of the fetus. Features include anemia, jaundice and brain damage. If serious and not treated, this condition may result in the death of the infant. Treatment of milder cases involves phototherapy while in serious cases blood transfusion and immunoglobulin injections during pregnancy and after the delivery of the infant are used. Between 0.1-0.2% of infants are born with rhesus disease.
  • Fetal alcohol syndrome. It may affect infants whose mothers consumed alcohol during pregnancy, especially in early pregnancy. Fetal alcohol syndrome is characterized by mental retardation, abnormalities of the facial features and problems in the central nervous system. It occurs in about 0.1% of infants.

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