What is DNA?

DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).
The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.
DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.
An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.

Surprisingly, while the DNA molecule is very long, it is stunningly simple. DNA looks like an incredibly long twisted ladder. This shape is called a double helix.
The sides of the ladder are a linked chain of alternating sugar and phosphate molecules. The rungs connect to the sugar molecules and are known as bases.
There are four bases - adenine (A), thymine (T), guanine (G) and cytosine (C). Each rung is made up of two bases that link together and because of their chemical nature, A will only link with T and G will only link with C.
DNA from all living organisms is made of the same sugar and phosphate molecules and the same four bases. Whether DNA is in your cells, those of a cactus, of a worm or a bacterium, it is made of the same chemicals and has the same structure.
The only difference is the order or the sequence of the bases in the DNA molecule. It is this sequence that is referred to as the genetic code, and why it is sometimes called the code of life.

Peripheral Neuropathy

A condition caused by damage to the nerves in the peripheral nervous system. The peripheral nervous system includes nerves that run from the brain and spinal cord to the rest of the body. Many of these nerves are involved with sensation and feeling things such as pain, temperature and touch. Up to one-third of people with HIV may get some symptoms of peripheral neuropathy. Peripheral neuropathy is usually felt at first as tingling and numbness in the hands and feet. Symptoms can be described as burning, shooting pain, throbbing, aching, and "feels like frostbite" or "walking on a bed of coals."

Peripheral neuropathy can sometimes be caused by HIV but is most commonly a side effect of drugs. Sometimes neuropathy can be caused by vitamin deficiencies or diabetes. Diagnosis of peripheral neuropathy is done by a physical exam. Tests of vitamin B12 levels, thyroid function and glucose levels are also used to check for vitamin deficiencies or diabetes. If peripheral neuropathy is caused by a drug, the symptoms usually get better once the drug is stopped, although it can take 6-8 weeks and the pain can actually get worse for a while.
Some other conditions can have the same symptoms and be confused with peripheral neuropathy. A symptom of CMV myelitis is a general weakening of the legs and is treated with anti-CMV drugs. Vacular myelopathy can cause numbness in the limbs and weakening of the spinal cord. New treatments are being studied for myelopathy. Herpes infections that cause symptoms of peripheral neuropathy are treated with acyclovir.

Genetic Code

The rules by which the base sequences of deoxyribonucleic acid (DNA) are translated into the amino acid sequences of proteins. Each sequence of DNA that codes for a protein is transcribed or copied into messenger ribonucleic acid (mRNA). Following the rules of the code, discrete elements in the mRNA, known as codons, specify each of the 20 different amino acids that are the constituents of proteins. During translation, another class of RNAs, called transfer RNAs (tRNAs), are coupled to amino acids, bind to the mRNA, and, in a step-by-step fashion provide the amino acids that are linked together in the order called for by the mRNA sequence. The specific attachment of each amino acid to the appropriate tRNA, and the precise pairing of tRNAs via their anticodons to the correct codons in the mRNA, form the basis of the genetic code. See also Deoxyribonucleic acid (DNA); Protein; Ribonucleic acid (RNA).
The genetic information in DNA is found in the sequence or order of four bases that are linked together to form each strand of the two-stranded DNA molecule. The bases of DNA are adenine, guanine, thymine, and cytosine, which are abbreviated as A, G, T, and C. Chemically, A and G are purines, and C and T are pyrimidines. The two strands of DNA are wound about each other in a double helix that looks like a twisted ladder. Each rung of the ladder is formed by two bases, one from each strand, that pair with each other by means of hydrogen bonds. For a good fit, a pyrimidine must pair with a purine; in DNA, A bonds with T, and G bonds with C.

Ribonucleic acids such as mRNA or tRNA also comprise four bases, except that in RNA the pyrimidine uracil (U) replaces thymine. During transcription a single-stranded mRNA copy of one strand of the DNA is made.
If two bases at a time are grouped together, then only 4 × 4 or 16 different combinations are possible, a number that is insufficient to code for all 20 amino acids that are found in proteins. However, if the four bases are grouped together in threes, then there are 4 × 4 × 4 or 64 different combinations. Read sequentially without overlapping, those groups of three bases constitute a codon, the unit that codes for a single amino acid.
The 64 codons can be divided into 16 families of four, in which each codon begins with the same two bases. With the number of codons exceeding the number of amino acids, several codons can code for the same amino acid. Thus, the code is degenerate. In eight instances, all four codons in a family specify the same amino acid. In the remaining families, the two codons that end with the pyrimidines U and C often specify one amino acid, whereas the two codons that end with the purines A and G specify another. Furthermore, three of the codons, UAA, UAG, and UGA, do not code for any amino acid but instead signal the end of the protein chain.

(Taken from Answers.com)

Polio

Polio (also called poliomyelitis) is a contagious, historically devastating disease that was virtually eliminated from the Western hemisphere in the second half of the 20th century. Although polio has plagued humans since ancient times, its most extensive outbreak occurred in the first half of the 1900s before the vaccination, created by Jonas Salk, became widely available in 1955.
At the height of the polio epidemic in 1952, nearly 60,000 cases with more than 3,000 deaths were reported in the United States alone. However, with widespread vaccination, wild-type polio, or polio occurring through natural infection, was eliminated from the United States by 1979 and the Western hemisphere by 1991.
Signs and Symptoms
Polio is a viral illness that, in about 95% of cases, actually produces no symptoms at all (called asymptomatic polio). In the 4% to 8% of cases in which there are symptoms (called symptomatic polio), the illness appears in three forms:
a mild form called abortive polio (most people with this form of polio may not even suspect they have it because their sickness is limited to mild flue)like symptoms such as mild upper respiratory infection, diarrhea, fever, sore throat, and a general feeling of being ill)
a more serious form associated with aseptic meningitis called nonparalytic polio (1% to 5% show neurological symptoms such as sensitivity to light and neck stiffness)
a severe, debilitating form called paralytic polio (this occurs in 0.1% to 2% of cases)
People who have abortive polio or nonparalytic polio usually make a full recovery. However, paralytic polio, as its name implies, causes muscle paralysis - and can even result in death. In paralytic polio, the virus leaves the intestinal tract and enters the bloodstream, attacking the nerves (in abortive or asymptomatic polio, the virus usually just stays in the intestinal tract). The virus may affect the nerves governing the muscles in the limbs and the muscles necessary for breathing, causing respiratory difficulty and paralysis of the arms and legs.
Contagiousness
Polio is transmitted primarily through the ingestion of material contaminated with the virus found in stool (poop). Not washing hands after using the bathroom and drinking contaminated water were common culprits in the transmission of the disease.
Prevention
In the United States, it's currently recommended that children have four doses of inactivated polio vaccination (IPV) between the ages of 2 months and 6 years.
By 1964, the oral polio vaccine (OPV), developed by Albert Sabin, had become the recommended vaccine. OPV allowed large populations to be immunized because it was easy to administer, and it provided "contact" immunization, which means that an unimmunized person who came in contact with a recently immunized child might become immune, too. The problem with OPV was that, in very rare cases, paralytic polio could develop either in immunized children or in those who came in contact with them.
Since 1979 (when wild polio was eliminated in the United States), the approximately 10 cases per year of polio seen in this country were traced to OPV.
IPV is a vaccine that stimulates the immune system of the body (through production of antibodies) to fight the virus if it comes in contact with it. IPV cannot cause polio.
In an effort to eradicate all polio, including those cases associated with the vaccine, the Centers for Disease Control and Prevention (CDC) decided to make IPV the only vaccine given in the United States. Currently, the CDC and American Academy of Pediatrics (AAP) recommend three spaced doses of IPV given before the age of 18 months, and an IPV booster given between the ages of 4 to 6, when children are entering school.
If you're planning to travel outside the United States, particularly to Africa and Asia (where polio still exists), be sure that you and your child receive a complete set of polio vaccinations.
Duration
Although the acute illness usually lasts less than 2 weeks, damage to the nerves could last a lifetime. In the past, some patients with polio never regained full use of their limbs, which would appear withered. Those who did fully recover might go on to develop post-polio syndrome (PPS) as many as 30 to 40 years after contracting polio. In PPS, the damage done to the nerves during the disease causes an acceleration of the normal, gradual weakness due to aging.
Treatment
In the height of the polio epidemic, the standard treatment involved placing a patient with paralysis of the breathing muscles in an "iron lung" - a large machine that actually pushed and pulled the chest muscles to make them work. The damaged limbs were often kept immobilized because of the confinement of the iron lung. In countries where polio is still a concern, ventilators and some iron lungs are still used.
Historically, home treatment for paralytic polio and abortive polio with neurological symptoms wasn't sufficient. However, asymptomatic and mild cases of abortive polio with no neurological symptoms might have been treated like the flu, with plenty of fluids and bed rest.

Pierre Robin Syndrome

This syndrome was described in 1923 by Pierre Robin in which he described airway obstruction associated with glossoptosis and hypoplasia of the mandible. Today this syndrome is characterized by retrognathia or micrognathia, glossoptosis, and airway obstruction. An incomplete cleft of the palate is associated with the syndrome in approximately 50% of these patients.
In patients with micrognathia (small jaw) or retrognathia, the chin is posteriorly displaced causing the tongue to fall backward toward the posterior pharyngeal wall. This results in obstruction of the airway on inspiration. Crying or straining by these children can often keep the airway open. However, when the child relaxes or falls asleep, airway obstruction occurs. Due to these respiratory problems, feeding may become very difficult. This can lead to a sequence of events: glossoptosis, airway obstruction, crying or straining with increased energy expenditure and decreased oral intake. This vicious cycle of events if untreated can led to exhaustion, cardiac failure, and ultimately death.

Treatment of this syndrome can be divided into conservative therapy versus surgical intervention. The majority of these patients can be managed by placing the infant in the prone position until adequate growth of the jaw occurs. This causes the jaw and the tongue to fall forward opening the airway. If this type of treatment fails the infant should then be considered for a tongue-lip adhesion (a procedure to pull the tongue forward) or a tracheostomy.
In children with severe underdevelopment of the lower jaw, a new technique called mandibular bone expansion is now available. This technique also called distraction osteogenesis involves placement of an expansion device that is turned daily to slowly lengthen the jaw. An external incision is required to make a surgical cut through the jaw bone with placement of pins that are secured to the expansion device. Once the amount of expansion of the bone has been obtained (4-5 weeks) the device is then kept in place until the bone gap heals with new bone formation (8 weeks). This technique can be performed at a very early age which is a significant advantage over the traditional technique of lower jaw lengthening.

Huntington's Disease

What is Huntington's Disease?

Huntington's disease (HD) results from genetically programmed degeneration of brain cells, called neurons, in certain areas of the brain. This degeneration causes uncontrolled movements, loss of intellectual faculties, and emotional disturbance. HD is a familial disease, passed from parent to child through a mutation in the normal gene. Each child of an HD parent has a 50-50 chance of inheriting the HD gene. If a child does not inherit the HD gene, he or she will not develop the disease and cannot pass it to subsequent generations. A person who inherits the HD gene will sooner or later develop the disease. Whether one child inherits the gene has no bearing on whether others will or will not inherit the gene. Some early symptoms of HD are mood swings, depression, irritability or trouble driving, learning new things, remembering a fact, or making a decision. As the disease progresses, concentration on intellectual tasks becomes increasingly difficult and the patient may have difficulty feeding himself or herself and swallowing. The rate of disease progression and the age of onset vary from person to person. A genetic test, coupled with a complete medical history and neurological and laboratory tests, helps physicians diagnose HD. Presymptomic testing is available for individuals who are at risk for carrying the HD gene. In 1 to 3 percent of individuals with HD, no family history of HD can be found.

Is there any treatment?
Physicians prescribe a number of medications to help control emotional and movement problems associated with HD. Most drugs used to treat the symptoms of HD have side effects such as fatigue, restlessness, or hyperexcitability. It is extremely important for people with HD to maintain physical fitness as much as possible, as individuals who exercise and keep active tend to do better than those who do not.

What is the prognosis?
At this time, there is no way to stop or reverse the course of HD. Now that the HD gene has been located, investigators are continuing to study the HD gene with an eye toward understanding how it cause disease in the human body.

What research is being done?
Scientific investigations using electronic and other technologies enable scientists to see what the defective gene does to various structures in the brain and how it affects the body's chemistry and metabolism. Laboratory animals are being bred in the hope of duplicating the clinical features of HD so that researchers can learn more about the symptoms and progression of HD. Investigators are implanting fetal tissue in rodents and nonhuman primates with the hope of understanding, restoring, or replacing functions typically lost by neuronal degeneration in individuals with HD. Related areas of investigation include excitotoxicity (overstimulation of cells by natural chemicals found in the brain), defective energy metabolism (a defect in the mitochondria), oxidative stress (normal metabolic activity in the brain that produces toxic compounds called free radicals), tropic factors (natural chemical substances found in the human body that may protect against cell death).

Avascular Necrosis

Avascular Necrosis
Avascular necrosis is a disease resulting from the temporary or permanent loss of the blood supply to the bones. Without blood, the bone tissue dies and causes the bone to collapse. If the process involves the bones near a joint, it often leads to collapse of the joint surface. This disease also is known as osteonecrosis, aseptic necrosis, and ischemic bone necrosis.
Although it can happen in any bone, avascular necrosis most commonly affects the ends (epiphyses) of long bones such as the femur, the bone extending from the knee joint to the hip joint. Other common sites include the upper arm bone, knees, shoulders, and ankles. The disease may affect just one bone, more than one bone at the same time, or more than one bone at different times. Avascular necrosis usually affects people between 30 and 50 years of age; about 10,000 to 20,000 people develop avascular necrosis each year. Orthopaedic doctors most often diagnose the disease.
The amount of disability that results from avascular necrosis depends on what part of the bone is affected, how large an area is involved, and how effectively the bone rebuilds itself. The process of bone rebuilding takes place after an injury as well as during normal growth. Normally, bone continuously breaks down and rebuilds - old bone is reabsorbed and replaced with new bone. The process keeps the skeleton strong and helps it to maintain a balance of minerals. In the course of avascular necrosis, however, the healing process is usually ineffective and the bone tissues break down faster than the body can repair them. If left untreated, the disease progresses, the bone collapses, and the joint surface breaks down, leading to pain and arthritis.
Avascular necrosis affects both men and women and affects people of all ages. It is most common among people in their thirties and forties. Depending on a person's risk factors and whether the underlying cause is trauma, it also can affect younger or older people.

Causes
Avascular necrosis has several causes. Loss of blood supply to the bone can be caused by an injury (trauma-related avascular necrosis or joint dislocation) or by certain risk factors (nontraumatic avascular necrosis), such as some medications (steroids), blood coagulation disorders, or excessive alcohol use. Increased pressure within the bone also is associated with avascular necrosis. The pressure within the bone causes the blood vessels to narrow, making it hard for the vessels to deliver enough blood to the bone cells.
Injury: When a joint is injured, as in a fracture or dislocation, the blood vessels may be damaged. This can interfere with the blood circulation to the bone and lead to trauma-related avascular necrosis. Studies suggest that this type of avascular necrosis may develop in more than 20% of people who dislocate their hip joint.
Steroid Medications: Corticosteroids such as prednisone are commonly used to treat diseases in which there is inflammation, such as systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, and vasculitis. Studies suggest that long-term, systemic (oral or intravenous) corticosteroid use is associated with 35% of all cases of nontraumatic avascular necrosis. However, there is no known risk of avascular necrosis associated with the limited use of steroids. Patients should discuss concerns about steroid use with their doctor.Doctors aren't sure exactly why the use of corticosteroids sometimes leads to avascular necrosis. They may interfere with the body's ability to break down fatty substances. These substances then build up in and clog the blood vessels, causing them to narrow. This reduces the amount of blood that gets to the bone. Some studies suggest that corticosteroid-related avascular necrosis is more severe and more likely to affect both hips (when occurring in the hip) than avascular necrosis resulting from other causes.
Alcohol Use: Excessive alcohol use and corticosteroid use are two of the most common causes of nontraumatic avascular necrosis. In people who drink an excessive amount of alcohol, fatty substances may block blood vessels, causing a decreased blood supply to the bones that results in avascular necrosis.
Other Risk Factors: Other risk factors or conditions associated with nontraumatic avascular necrosis include Gaucher's disease, pancreatitis, radiation treatments and chemotherapy, decompression disease, and blood disorders such as sickle cell disease.

Symptoms
In the early stages of avascular necrosis, patients may not have any symptoms. As the disease progresses, however, most patients experience joint pain - at first, only when putting weight on the affected joint, and then even when resting. Pain usually develops gradually and may be mild or severe. If avascular necrosis progresses and the bone and surrounding joint surface collapse, pain may develop or increase dramatically. Pain may be severe enough to limit the patient's range of motion in the affected joint. In some cases, particularly those involving the hip, disabling osteoarthritis may develop. The period of time between the first symptoms and loss of joint function is different for each patient, ranging from several months to more than a year.

Diagnosis
After performing a complete physical examination and asking about the patient's medical history (for example, what health problems the patient has had and for how long), the doctor may use one or more imaging techniques to diagnose avascular necrosis. As with many other diseases, early diagnosis increases the chances of treatment success.
X-Ray: An X-ray is a common tool that the doctor may use to help diagnose the cause of joint pain. It is a simple way to produce pictures of bones. The X-ray of a person with early avascular necrosis is likely to be normal because X-rays are not sensitive enough to detect the bone changes in the early stages of the disease. X-rays can show bone damage in the later stages, and once the diagnosis is made, they are often used to monitor the course of the condition.
Magnetic Resonance Imaging (MRI): MRI is quickly becoming a common method for diagnosing avascular necrosis. Unlike X-rays, bone scans, and CT (computed/computerized tomography) scans, MRI detects chemical changes in the bone marrow and can show avascular necrosis in its earliest stages. MRI provides the doctor with a picture of the area affected and the bone rebuilding process. In addition, MRI may show diseased areas that are not yet causing any symptoms.
Bone Scan: Also known as bone scintigraphy, bone scans are used most commonly in patients who have normal X-rays. A harmless radioactive dye is injected into the affected bone and a picture of the bone is taken with a special camera. The picture shows how the dye travels through the bone and where normal bone formation is occurring. A single bone scan finds all areas in the body that are affected, thus reducing the need to expose the patient to more radiation. Bone scans do not detect avascular necrosis at the earliest stages.
Computed/Computerized Tomography (CT Scan): A CT scan is an imaging technique that provides the doctor with a three-dimensional picture of the bone. It also shows "slices" of the bone, making the picture much clearer than X-rays and bone scans. Some doctors disagree about the usefulness of this test to diagnose avascular necrosis. Although a diagnosis usually can be made without a CT scan, the technique may be useful in determining the extent of bone damage.
Biopsy: A biopsy is a surgical procedure in which tissue from the affected bone is removed and studied. Although a biopsy is a conclusive way to diagnose avascular necrosis, it is rarely used because it requires surgery.
Functional Evaluation of Bone: Tests to measure the pressure inside a bone may be used when the doctor strongly suspects that a patient has avascular necrosis, despite normal results of X-rays, bone scans, and MRIs. These tests are very sensitive for detecting increased pressure within the bone, but they require surgery.