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HIV AIDS What is HIV/AIDS? The term AIDS refers to the most advanced stages of an infection caused by the human immunodeficiency virus (HIV). The current definition of AIDS includes: All HIV-infected people who have fewer than 200 CD4+ T cells (also called T4 cells). These cells

Atherosclerosis What is atherosclerosis? Atherosclerosis is thickening of the walls of the arteries. It is also known as hardening of the arteries. It is caused by a buildup of plaque in the inner lining of an artery. Plaque is made up of deposits of fatty substances, cholesterol

Allergy Overview What are allergies? Allergies are due to a problem with the body's immune system. Most allergic reactions happen when the immune system reacts to a false alarm. Normally the immune system attacks harmful things, such as viruses or bacteria. But sometimes it

Shingles What is shingles? Shingles (herpes zoster) is a common infection of the nerves. It is caused by a virus. Shingles set off a painful rash or small blisters on an area of skin. It can appear anywhere on the body, but it typically appears on only one side of the face or

Astrocytoma in Children What is an astrocytoma in children? An astrocytoma is a type of brain tumor. A brain tumor is an abnormal growth of tissue in the brain. The brain is part of the central nervous system (CNS). The CNS also includes the spinal cord. The main parts of the

Sickle Cell Disease in Children What is sickle cell disease in children? Sickle cell disease (SCD) is a blood disorder that a child is born with. It's passed down through a parent’s genes. Children with SCD make an abnormal type of hemoglobin. This is the protein in red blood

Down Syndrome (Trisomy 21) in Children What is Down syndrome in children? Down syndrome is a genetic disorder. It is also called trisomy 21. It includes certain birth defects, learning problems, and facial features. A child with Down syndrome also may have heart defects and

22q11.2 Deletion Syndrome in Children What is 22q11.2 deletion syndrome in children? The 22q11.2 deletion syndrome (22q11.2DS) is a genetic disorder. In children with this syndrome, a tiny piece of chromosome 22 is missing. This can cause many health problems. These problems may

Hodgkin Lymphoma in Children What is Hodgkin lymphoma in children? Hodgkin lymphoma is also called Hodgkin disease. It's a type of cancer that starts in the lymphatic system. The lymphatic system is part of the immune system. It helps to fight diseases and infections. The

Head Injury What is a head injury? A head injury is a broad term that describes many injuries that occur to the scalp, skull, brain, and underlying tissue and blood vessels in the head. Head injuries are also commonly referred to as brain injury, or traumatic brain injury (TBI)