Defining AIDS

Defining AIDS

The CDC presented its first definition of AIDS in 1982. The CDC recommended that physicians diagnose AIDS if a person has an illness known to be caused by immune deficiency, as long as there is no known cause for this immune deficiency. (Radiation therapy for cancer and certain drugs also may impair the immune system). As more information became known about the course of HIV infection and the nature of the virus itself, this definition of AIDS was revised repeatedly to expand the list of illnesses considered diagnostic indicators of the disease. Early definitions were based on the opportunistic infections commonly found in HIV-infected men. As a result, many women who did not have symptoms covered in the official AIDS definition were denied disability benefits and AIDS-related drug therapies.

The current definition of AIDS was created in 1993 and includes 26 opportunistic infections and cancers, known as diagnostic indicators, which affect both men and women. The definition also emphasizes the importance of the level of CD4 cells in the blood. Today doctors make the diagnosis of AIDS in anyone with a CD4 count below 200 cells per micro-liter of blood, regardless of the associated illnesses they may have.

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Biochemistry in 1989: Genetic Engineering (Erythropoietin for Anemia)

In June the U.S. Food and Drug Administration (FDA) approved the marketing of a genetically engineered form of erythropoietin (EPO) for use in treating anemia in patients with severe kidney disease. EPO is a hormone produced in the kidney that stimulates the growth of red blood cells. The new drug, epoetin alfa (sold under the name Epogen), was expected to benefit many of the more than 90,000 people in the United States who regularly undergo dialysis to remove toxic chemicals from their blood because their kidneys have failed. Dialysis destroys red blood cells, making the patients anemic. Also, many dialysis patients require frequent transfusions, which lead to a toxic buildup of iron (from destroyed red cells) in their blood; EPO should ease that problem.

Later in June the FDA gave limited approval for another use of EPO. The drug was authorized as an ‘investigational new drug for treatment,’ for use in people with AIDS who suffer from anemia, either from the virus that causes the disease or because they are taking zidovudine (previously called AZT) to control the disease’s progression. Zidovudine kills red blood cells, and EPO helps to replace them.

 

Biochemistry in 1989: Genetic Defects (Diabetes)

Researchers from the University Of Pittsburgh School Of Medicine have developed a genetic test that can detect susceptibility to Type I diabetes, the most serious form of diabetes and one that is normally controlled by insulin injections. By studying DNA in white blood cells, Massimo Trucco and colleagues reported in June, they can identify children who are susceptible to the disease, which scientists believe develops after an encounter with a triggering agent, such as certain viral infections.

Trucco noted that physicians now have no way to prevent the development of Type I diabetes, but experiments in animals suggest that such treatments may be possible in the future. For the meantime, he added, the test will allow parents to monitor their children for initial signs of the disease, which often resemble influenza. Many children are first diagnosed in emergency rooms, where they have been taken in a diabetic coma because early symptoms were not recognized.

 

Biochemistry in 1989: Genetic Defects (Retinitis Pigmentosa)

By studying more than 100 members of an Irish family with a high incidence of retinitis pigmentosa (RP) — a hereditary condition that causes degeneration of the eye’s retina and subsequent blindness and afflicts more than 100,000 Americans and 1.5 million people worldwide — researchers from Ireland and the United States found the location of the gene that causes one form of it. The discovery is particularly important because researchers have no idea how the disease develops and no therapy is available for it.

Geneticists Stephen Daiger of the University of Texas Health Sciences Center in Houston and Peter Humphries of Trinity College in Dublin announced in July that the gene for a form of RP called autosomal dominant RP is located in a small region of chromosome 3. In autosomal dominant RP, when one parent has the disease, a child has a 50 percent chance of inheriting it. Discovery of the gene’s location makes possible prenatal screening for the defect and should lead to new information about how the disease occurs.

 

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Biochemistry in 1989: Genetic Defects (Prenatal Screening)

It may eventually be possible to conduct prenatal screening for certain genetic defects, such as sickle-cell anemia, cystic fibrosis, and phenylketonuria, using only blood from the mother, thereby eliminating the small risk of miscarriage associated with amniocentesis, according to Diana Bianchi of Children’s Hospital in Boston.

A pregnant woman‘s blood contains a small number of red blood cells from the fetus, perhaps one such fetal cell in a billion of the mother’s cells. Bianchi reported in July that it is possible to isolate these fetal cells using antibodies that bind only to them. Unlike adult red blood cells, fetal cells contain a nucleus, with chromosomes, which can be tested for the presence of genetic defects. But the process is ‘really at the limits of technology,’ Bianchi said, and probably could not be used routinely for several years.

Biochemistry in 1989: Genetic Defects (Pygmies)

Scientists have long wondered why African Pygmies rarely grow beyond the height of 4 feet 10 inches, even though they appear to have normal quantities of human growth hormone in their blood. Now, researchers from the Northwestern University Medical School and the University of Florida may have found the answer. They reported in June that Pygmies seem to have low levels of growth hormone receptors, the cellular proteins to which growth hormone must bind so that it can signal tissues to continue their growth.

In a separate study, also reported in June, endocrinologists at the University of Oklahoma Health Sciences Center in Oklahoma City studied a group of American teenagers who were short even though they too apparently produced normal amounts of human growth hormone. This group also had a shortage of the growth hormone receptor. The researchers speculated that it might be possible to increase stature in such children by administering a protein that is normally produced in cells as a result of the hormone binding to the receptor.

 

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Biochemistry in 1989: Genetic Defects (Cystic Fibrosis)

A team of U.S. and Canadian scientists in August announced the discovery of the gene that, when defective, causes cystic fibrosis, the most common fatal genetic disease in North America. The disorder causes mucus to collect in the lungs and pancreas, inviting chronic bacterial infections. Cystic fibrosis afflicts about 30,000 people in the United States, most of who do not live past their 20s. The gene was found on chromosome 7 by the researchers, headed by Francis Collins of the University of Michigan and Lap-Chee Tsui of the Hospital for Sick Children in Toronto.

A person has to inherit two copies of the defective gene — one from each parent — in order to get the disease. Those who inherit one defective gene and one normal gene (about 12 million people in the United States) do not develop cystic fibrosis but are carriers of it. The discovery of the gene may lead to treatments for the disease; one suggested approach involves injecting healthy genes into viruses that would insert themselves into lung tissue, where the healthy genes would replace defective ones.

 

Biochemistry in 1989: Genetic Engineering (Speeding Wound Healing)

A genetically engineered substance called epidermal growth factor accelerated the healing of wounds in 12 people, a team headed by Gregory L. Brown of the University of Louisville in Kentucky reported in July. The demonstration marked the first time that such a substance, which belongs to a large family of naturally occurring growth factors, has been found to be effective in humans.

The 12 individuals required skin grafts for various reasons, primarily because of burns. One site on each patient was treated with the growth factor while a second site was not. The treated sites healed, on average, about 1.5 days faster than the untreated sites. Physicians believe the growth factor may be particularly valuable in treating patients with severe burns or chronic wounds, such as bedsores and foot ulcers.

Biochemistry in 1989: Genetic Engineering (Respiratory Distress Syndrome)

Nearly 40,000 of the 250,000 premature babies born in the United States each year develop a progressively increasing difficulty with breathing called respiratory distress syndrome. This problem is treated by raising the level of oxygen in the newborn‘s incubator by as much as 100 percent. But the high oxygen levels generate oxygen ‘free radicals,’ highly reactive chemicals that cause bronchopulmonary dysplasia in 20 to 30 percent of the infants treated for respiratory distress syndrome. Bronchopulmonary dysplasia is a condition in which fibrous tissue develops in the lungs, sometimes causing respiratory failure. In March, Bio-Technology General Corporation of New York City began clinical trials of genetically engineered superoxide dismutase (SOD) for treatment of the condition in premature infants. SOD protects the infants by destroying the free radicals. Recent tests of SOD obtained from cows have been largely successful, and pediatricians believe human SOD produced by genetic engineering techniques should be even better because it will not stimulate an immune reaction.

 

Diagnosing AIDS

Structure of Human Immunodeficiency Virus

Diagnosing AIDS involves some important tests. Physicians prefer to differentiate between people who have HIV infection and those who have AIDS. The Centers for Disease Control and Prevention (CDC), based in Atlanta, Georgia, recommends that physicians reserve the diagnosis of AIDS for HIV-infected people whose CD4 count falls below 200 cells per micro-liter of blood. A diagnosis of AIDS can also be made without confirmation of CD4 levels if someone who has no other reason for immune system damage develops an opportunistic disease. Diagnosing and treating AIDS is however a problem owing to the inability of scientist to give permanent remedy for the scourge.

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