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Genetic Disorders

Some genetic disorders can be corrected, while others cannot.

A genetic disorder is often caused by mutations that occur during DNA replication. [©Shutterstock, 2010]
©Shutterstock, 2010
A genetic disorder is often caused by mutations that occur during DNA replication.

Genetic Disorders

Genetic disorders are abnormalities or diseases caused by a genetic mutation that typically occurs during DNA replication. Non-genetic disorders and diseases are caused by viruses, infections, trauma, chemical imbalances, lifestyle practices and exposure to certain chemicals or compounds (such as smoking).

Types of Defects

There are four kinds of genetic disorders:

  • Mendelian or single-gene disorders that are caused by a single mutation or pattern of mutations in the DNA sequence. This occurs in 1 out of every 200 births and includes sickle cell anemia, cystic fibrosis, Huntington's disease (degenerative nerve cells in the brain) and muscular dystrophy.
  • Multifactorial inheritance includes both mutations in multiple genes as well an environmental factors that cause disease. Examples include breast cancer, heart disease, diabetes and Alzheimer's disease.
  • Chromosomal disorders are abnormal chromosomes or the wrong number of chromosomes. The most common example is Down syndrome, which occurs when a person has 3 copies of chromosome 21.
  • Mitochondrial, a rare type of genetic disorder, is caused by mutations in the nonchromosomal DNA of the mitochondria of cells. Parkinson's disease, stroke and Alzheimer's disease are linked to mitochondrial disorders.

Genetic disorders and diseases include achondroplasia (dwarfism), fetal alcohol syndrome, high cholesterol, hemophilia, celiac disease, birth defects, Marfan syndrome (tall and lanky limbs) and Turner syndrome (a female missing an X chromosome). Genetic disorders can also affect a person's ability to tolerate certain drugs, such as the malaria drug primaquine.

Research of Genetic Disorders

Because many human diseases have a genetic component, research in genetic disorders has exploded in recent years. The National Human Genome Research Institute (NHGRI) is conducting extensive research on understanding how genetic disruptions in signaling pathways and transcription factors can contribute to disease.

The Institute is researching a variety of common disorders, such as the genetic link to cancer, as well as numerous orphan and rare diseases. NHGRI's clinical research program is involved in far-reaching genetic studies of numerous disorders, including as hyperactivity, immune system, birth defects, development and behavior, bleeding, kidney failure, joints and brain malformation. The Institute is also studying specific populations around the world prone to genetic abnormalities: Colombians living in the Andes Mountains; Old Order Amish communities in Lancaster, Pennsylvania; Italians in southern Italy; and populations in West Africa and Finland.

For more information, consult Genes and Disease, a collection of articles on the link between genes and disease, published by the National Library of Medicine and the National Center for Biotechnology Information. The book identifies and summarizes more than 80 genetic disorders.

Genetic Testing of Newborns

People who are aware of genetic disorders in their family should get genetic testing or genetic counseling if they plan to start a family. Infants should be examined and tested at birth for any genetic abnormalities. The March of Dimes recommends all newborns be screened using a few drops of blood taken from the infant's heel. A hospital can test for up to 50 genetic disorders, including sickle cell anemia, hypothyroidism, galactosemia (inability to metabolize sugar) and phenylketonuria (inability to process amino acids). Tests can also be performed on the baby while its in the womb, using such procedures as amniocentesis and chorionic villus sampling (CVS).

Newborns can also be checked visually for abnormalities. Tulane University School of Medicine offers advice for testing infants. Examine the head and neck for wide set eyes, cleft palate, excessive hair on the body, flattened or triangular face and low-set ears. Check the eyes for failure of the iris to close or for cataracts. Examine the finger and thumb position, simian crease in the palm, extra fingers and club feet. Check for congenital heart defects, missing kidney or kidney abnormalities. And as the child gets older, look for signs of mental retardation and developmental disabilities.

Test Early and Treat Early

Some genetic defects are common, such as a cleft palate, and can be corrected with minor surgery. Some are common but very serious. Congenital heart defects affect 35,000 newborns each year, according to the American Heart Association. Some defects are rare. Krabbe Disease, in which infants lose brain and motor functions and rarely live past two years, affects 1 in 100,000 babies.

The United States screens newborns for genetic disorders. In 2004, roughly 4,000 infants were diagnosed with metabolic disorders, according to the March of Dimes. A timely and accurate diagnosis of genetic abnormalities allows the doctor and parents to address and treat any disorders early.

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