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Glossary

  • p: the short arm of a chromosome.
  • Palpitations: abnormal heart beats, either too fast or too slow.
  • Paralysis: a loss or impairment of voluntary movement in a body part.
  • Pathway:  a sequence of steps by which one biological compound is converted to another.
  • Penetrance: in genetics refers to how likely it is that a person who carries a given genetic mutation will show symptoms of the disease. Most of the inherited porphyrias (including those with dominant inheritance) have low penetrance, such that many people with the gene show no signs of illness. This accounts for “skipped generations” in a given family that is known to harbor a porphyria gene.
  • Peripheral nervous system (PNS):  the part of the nervous system outside the central nervous system (brain and spinal cord).
  • Peripheral neuropathy: numbness, tingling, or pain, usually in the hands and feet, reflecting damage to the peripheral nerves.
  • Peritoneal dialysis: a method of dialysis for the treatment of kidney failure; method for removing waste products such as potassium and urea, as well as free water from the blood when the kidneys are in renal failure.
  • Phenotype: the actual appearance of the person or disease, with reference to the underlying genetic state.
  • Phlebotomy: also known as venesection, blood-letting; removing blood. The procedure is used to reduce total body iron in people with porphyria cutanea tarda or hemochromatosis.
  • Photoactive: molecules are those which react to light, typically by gaining and subsequently releasing energy.
  • Photodermatitis: inflammation of the skin caused by exposure to sunlight.
  • Photodynamic therapy: a treatment method that uses chemical activated by light.
  • Photosensitivity: the increased reactivity of skin to sunlight caused by a disorder such as porphyria; sometimes referred to as “phototoxicity.”
  • Plasma:  liquid part of the blood in which blood cells are suspended.
  • Porphobilinogen (PBG): the second intermediate in the heme biosynthetic pathway. A large increase in urinary or plasma PBG is the signature finding in acute attacks of porphyria.
  • Porphobilinogen deaminase (PGBD): another name for hydroxymethylbilane synthase.
  • Porphyria: a group of disorders caused by deficiencies of specific enzymes in the pathway to make heme.
  • Porphyria Cutanea Tarda (PCT): a cutaneous and hepatic type of porphyria due to deficient activity of the enzyme, uroporphyrinogen decarboxylase.
  • Porphyrin precursors: refers to 5-aminolevulinic acid and porphobilinogen.
  • Porphyrin synthesis:  the production of porphyrins.
  • Porphyrin synthetic pathway: Porphyrin synthetic pathway
  • Porphyrin(s): a compound that combines with iron to make heme; excess porphyrins are present in individuals with porphyria.
  • Porphyrogenic: refers to an agent or drug that increases circulating porphyrins or precursors and may precipitate a porphyric attack.
  • Precursors: compounds that participates in the chemical reaction that produces another compound.  It is the precursor that will accumulate when such a reaction does not happen.
  • Predispose:  make someone susceptible to something beforehand.
  • Prenatal: before birth.
  • Prevalence: the term describing how common or how uncommon a particular disease is in a population.  For example, South Africa has a high prevalence of VP, so the condition is common.
  • Primarily: occurring first, of most importance.
  • Production: the act or process of making a specific product.
  • Prognosis: the anticipated outcome.
  • Protein: compounds encoded by specific genes that are essential to all living cells, simplified by body processes to simple alpha-amino acids.
  • Protoporphyrin: a compound made in the pathway of heme biosynthesis.  Protoporphyrin is excreted in the stool, and is commonly measured by porphyrin laboratories in stool and red blood cells.
  • Protoporphyrin IX: an intermediate in heme biosynthesis pathway.
  • Protoporphyrinogen:   a compound made in the pathway of heme biosynthesis.
  • Protoporphyrinogen oxidase (PPO):  the seventh enzyme in the heme biosynthesis pathway; a deficiency results in autosomal dominant Variegate Porphyria (VP), an acute porphyria.
  • Pseudoporphyria: a person usually with renal failure and on hemodialysis, who has skin disease similar to porphyria cutanea tarda but with normal or only mildly elevated porphyrins.
  • Puberty:  the process of physical changes by which a child 's body becomes an adult body capable of reproduction.
  • Puberty: the process of physical changes by which a child 's body becomes an adult body capable of reproduction.
  • Pyrrole: a ring structure that is one-quarter of a heme molecule, a building block in heme production.