retinitis pigmentosa A group of inherited disorders in which abnormalities of the photoreceptors (the rods and cones) of the retina lead to progressive visual loss. Abbreviated RP. People with RP first experience defective dark adaptation (night blindness), then constriction of the visual field (tunnel vision), and eventually, late in the course of the disease, loss…
retinitis pigmentosa and deafness See Usher syndrome.
retinoblastoma A malignant eye tumor usually seen in children, that arises in cells in the developing retina that contain cancer-predisposing mutations in both copies of the gene RB1. Abbreviated RB. The most common sign of RB is a white pupillary reflex to light (leukocoria). There are two forms of RB: hereditary and sporadic. The inherited…
retinoic acid syndrome A disorder due to the cancer treatment retinoic acid characterized by fever, difficulty breathing, chest pain, lung infiltrates, fluid around the lungs and heart, and hypoxia (lack of oxygen) that develops in some patients receiving retinoic acid therapy. It usually develops within 30 days of treatment. Steroids and chemotherapy can be used…
retinopathy Any disease of the retina, the lightsensitive membrane at the back of the eye. The type of retinopathy is often specified, such as arteriosclerotic retinopathy, diabetic retinopathy, or hypertensive retinopathy.
retrograde intrarenal surgery A procedure for performing surgery within the kidney by using a viewing tube called a fiber-optic endoscope. Abbreviated RIRS. In RIRS, the scope is placed through the urethra into the bladder and then through the ureter, into the urine-collecting part of the kidney. RIRS may be done to remove a stone. The…
retropubic prostatectomy Surgical removal of the prostate through an incision in the abdomen.
retrosternal Behind the sternum (breastbone).
retrovirus A virus that is composed not of DNA but of RNA. Retroviruses have an enzyme, called reverse transcriptase, that gives them the unique property of transcribing their RNA into DNA after entering a cell. The retroviral DNA can then integrate into the chromosomal DNA of the host cell, to be expressed there. HIV is…
Rett syndrome A neurological disease that affects girls only and is one of the most common causes of mental retardation in females. Girls with the syndrome show normal development during the first 6 to 18 months of life, followed first by a period of stagnation and then by rapid regression in motor and language skills….
reversal of organs, total Complete transposition of the thoracic and abdominal organs from right to left, placing the heart in the right side of the chest, and so on. Organs appear as if in mirror image when examined or X-rayed. Total reversal of organs has been estimated to occur in about 1 in 6,000 to…
reverse genetics In molecular genetics, identifying genes purely on the basis of their position in the genome, with no knowledge whatsoever of the gene product. In classic genetics, the traditional approach was to find a gene product and then try to identify the gene itself. Also known as positional cloning.