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Birth Defects and Developmental Disabilities - Illustrated Article

The March of Dimes Birth Defects Foundation defines "birth defects" as: an abnormality of structure, function, or metabolism (body chemistry) present at birth that results in physical or mental disability, or is fatal. To date, researchers have identified thousands of different birth defects. Currently, birth defects rank as the leading cause of death for infants during the first year of life.

Birth defects can be caused by different factors, such as:

  • Genetic problems that result from the failure of one or more genes to work properly
  • Problems with the number or structure of chromosomes, such as extra ormissing groups of genes
  • Things that happen to a woman during pregnancy, such as getting rubella or Germanmeasles while pregnant, having untreated or uncontrolled diabetes while pregnant, beingaround or in contact with dangerous chemicals in the environment while pregnant, or usingdrugs or alcohol during pregnancy

These factors can change normal infant growth or development resulting in different types of birth defects, such as:

  • Physical problems with body parts or structures
    - Some physical problems include cleft (has a gap or split) lip or cleft palate, heart defects, and abnormal limbs, such as a clubfoot.
  • Functional problems with how a body part or body system works
    - These problems areoften called developmental disabilities and can include things like:
  • Nervous system or brain problems
    - such as learning disabilities, behavioral disorders,speech or language difficulties, muscle spasms or convulsions, and movement trouble
  • Sensory problems
    - such as cataracts of the eyes, blindness, hearing loss, or deafness
  • Metabolic disorders
    - involve a body process or chemical pathway or reaction, such as conditions that limit the body's ability to get rid of waste materials or harmful chemicals
  • Degenerative disorders
    - are conditions that might not be obvious at birth, but steadily make worse one or more aspects of healthIn some cases, birth defects can result from a combination of these factors, or they can affect many parts or processes in the body, which may lead to both physical and functional problems, to different degrees. Some of these types of birth defects and developmental disabilities are described below.

Physical Birth Defects
Researchers and health care providers use the term neural tube defects to describe one important category of birth defects. These problems are related to the growth and development of the brain and spinal cord. Neural tube defects can include conditions like anencephaly (an-in-SEFF-a-lee), a fatal condition in which much of the brain does not develop; and spina bifida, in which the membranes around the spinal cord don't close properly, or the cord itself is not completely normal. People with spina bifida may have difficulty walking or be unable to walk without help, or they may have abnormal limbs. The condition is also associated with other structural problems with the body. In half of all babies born with spina bifida, the resulting problems are severe enough to result in death.

Research in this area has shown that getting the right amount of folic acid before and during pregnancy can prevent most neural tube defects. The U.S. Public Health Service recommends that women of childbearing age get at least 400 milligrams of folic acid each day, through food sources and/or supplements. Health care providers recommend that women supplement their diets with folic acid for three months before conception, and then for at least the first three months of pregnancy. Findings from research supported by the NICHD and other agencies indicate that the right amount of folic acid can help prevent certain birth defects and other problems during pregnancy. For more information on this and other prenatal recommendations, please visit the Prenatal Care section of this Web site. For more information on this research, read the news releases about folic acid.

In some cases, spina bifida can be detected in the womb. This early detection may allow surgeons to correct the spinal cord problems before birth, but researchers have yet to confirm this idea. If this research proves effective, it could alleviate many of the lasting effects of these problems. To learn more about this type of surgery, the NICHD is supporting the MOMS (Management of Meningomyelocele Study) trial, a clinical trial that will compare the safety and effectiveness of surgery before birth, with surgery performed right after birth in correcting spinal cord problems. The research is part of the Maternal-Fetal Medicine Unit (MFMU) Network, an NICHD-supported program that uses 14 sites around the country to conduct clinical trials related to the mechanisms of pregnancy and birth.

Functional Birth Defects/Developmental Disabilities
This complex group of birth defects involves a problem with the operation of a part of the body, a system in the body, or a process or pathway in the body. Although this information groups these developmental disabilities into general categories, many functional birth defects affect multiple body parts or systems. For example, a metabolic disorder may lead to nervous system or brain problems.

Nervous System/Brain Problems
As mentioned above, some birth defects affect the functioning of the brain, which can impact intelligence and learning. This section describes some of the more commonly known functional birth defects.

Mental Retardation
The term "mental retardation" describes a certain range of scores on an IQ (intelligence quotient) test. Mental retardation can result from a number of different birth defects, including:

  • In the past, a specific type of bacterial infection, called Hib, was a leading cause of mental retardation in the United States. But, as a result of NICHD-supported research on this infection, researchers funded by the NICHD were able to develop a vaccine to prevent the infection from occurring. Since the discovery of the vaccine, Hib has been nearly eliminated in the United States, and in other areas where the vaccine is available. As a result, Hib is also no longer a cause of mental retardation in the United States and other areas.
  • Down syndrome describes a set of mental and physical characteristics related to having an extra copy of a specific chromosome, Chromosome 21. This set of symptoms includes mental retardation. Interventions and treatments for the symptoms of Down syndrome can allow many individuals with this condition to live healthy, productive lives.
  • Fragile X syndrome is the most common inherited form of mental retardation. Parents with few or no symptoms can pass the condition on to their children through genes. A defect in a specific part of a specific gene, called the Fragile X Mental Retardation 1 gene, or FMR1, causes the body to produce low amounts or none of a certain protein. This protein is vital to normal brain development; without enough of it, the brain doesn't grow properly, leading to the symptoms of Fragile X.

Autism Spectrum Disorders
Other developmental disabilities include problems like autism spectrum disorders, a range of problems that can affect a person's ability to communicate, social skills, and intelligence. Because autism is diagnosed on a spectrum, people with this condition can be severely affected, or have only mild symptoms; but they all have a type of autism.

Sensory-related Developmental Disabilities
Sensory-related problems are often an important part of complex birth defect patterns. For instance, children with congenital rubella, a collection of problems that a child whose mother had rubella or German measles while pregnant may have, are likely to be deaf, and to develop cataracts of the eyes. Children with Williams syndrome have trouble seeing spatial relationships between objects around them. Those with Fragile X syndrome are often very sensitive to loud noises; they may overreact or have outbursts in reaction to such sounds.

The NICHD's research on birth defects has been helpful in understanding the timing of many sensory-related birth defects. That is, the research allowed scientists to pinpoint at what point in development certain problems occurred. The National Institute on Deafness and Other Communication Disorders and the National Eye Institute conduct and support research into various types of sensory-related birth defects, their treatments and interventions, and different services available for families affected by these conditions.

Metabolic Disorders
This group of functional birth defects affects a person's metabolism, which is the way the body builds up, breaks down, and otherwise processes the materials it needs to function. For example, digestion, how your body breaks down food into its smaller parts, is a metabolic process. Two commonly known metabolic disorders include:

  • Phenylketonuria (fee-nill-key-toe-NERR-ee-uh), also called PKU, is a condition in which a problem with a specific enzyme, a protein that speeds up certain chemical reactions, causes mental retardation. NICHD-supported researchers developed a dietary therapy that helps to balance the amount of this enzyme in the body, which has almost eliminated mental retardation in people with PKU. Conclusions from the NIH Consensus Development Conference on PKU: Screening and Management recommend that this dietary therapy continue throughout life. Women known to have PKU should follow the diet while they are pregnant to prevent mental retardation in their children.
  • Hypothyroidism (high-poe-THIGH-roid-izm) is a hormonal condition that, if left untreated in a pregnant woman, can cause mental retardation in her baby. The thyroid is a gland in the body that makes a chemical signal called a hormone. Hormones help to regulate certain functions in the body, including puberty and pregnancy. Without enough thyroid hormone in the mother's body, the fetus' brain won't develop correctly, resulting in mental retardation.

NICHD-supported researchers found that, by identifying women who have this condition early in or before pregnancy, treatments to get the level of thyroid hormone back to normal can prevent mental retardation in some cases. In addition, NICHD research found that children who are born with hypothyroidism could also be treated with thyroid hormone to prevent many of the long-term effects of this condition.

Degenerative Disorders
Some infants born with degenerative disorders appear normal at birth, but then lose abilities or functions due to the in condition. In these cases, the defect is usually not detected until an older age, when the child or person starts to show signs of a problem. Degenerative disorder can cause physical, mental, and sensory problems, depending on the specific defect.

In one type of degenerative disorder, early onset X-linked adrenoleukodystrophy (add-ree-know-loo-koe-diss-troe-fee), also called X-ALD, boys develop normally until between ages four and eight. After this point, they begin to lose brain and nervous system function. Eventually, boys with X-ALD lose so much of their brain and neural abilities that they appear to be in a "frozen" state, unable to move and communicate. X-ALD was the focus of the movie Lorenzo's Oil, which described one family's efforts to spur scientific progress.

Another type of degenerative birth defect is Rett syndrome. This disorder, which usually affects girls, is caused by a specific genetic abnormality.

The NICHD's efforts to understand these types of birth defects focus on screening techniques that allow early detection of these problems, and strategies to treat or relieve some of the symptoms of these conditions. Other work is underway to find the cellular mechanisms or genetic markers for these conditions.

Source: National Institute of Child and Human Development
National Institutes of Health



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