Glossary

Hallucinations: seeing, hearing, feeling something that is not really there while a person is awake and conscious; the incorrect perceptions of any of the senses.
Hematin: a red to blackish-brown component formed in the decomposition or breaking down of hemoglobin.
Heme: a porphyrin containing iron. It is the part of hemoglobin that binds oxygen, carrying it from the lungs to the rest of the body. In the liver, heme is present in cytochromes, which also bind oxygen needed for a variety of liver functions.
Heme arginate: a heme preparation used in the treatment of porphyria in Europe but not available in the US.
Heme biosynthesis: the formation of heme from glycine and succinyl-CoA.
Heme biosynthesis pathway: the series of enzyme steps involved in the formation of heme.
Heme biosynthetic cascade: see Heme biosynthetic pathway.
Hemin (trade name Panhematin®): a commercial form of heme, suitable for human use.
Hemochromatosis: an autosomal recessive, genetic disorder, which leads to the accumulation of large amounts of iron in many organs, especially in the liver.
Hemodialysis: see Dialysis.
Hemoglobin (Hb, Hgb): a specific protein in human red blood cells that contains iron and carries oxygen to other tissues in the body.
Hemolysis: the breakdown of the red blood cells (RBC's).
Hemolytic anemia: anemia resulting from hemolysis in the circulation.
Hemoproteins: proteins that contain heme.
Hepatic: pertaining to the liver.
Hepatitis: an inflammation of the liver from any cause: which include alcohol misuse, hepatitis C and B infections and hemachromatosis.
Hepatocellular cancer: primary liver cancer (originating in the liver).
Hepatocytes: cells in the liver.
Hepatoerythropoietic Porphyria (HEP): the autosomal recessive form of familial Porphyria Cutanea Tarda (PCT).
Hepatomegaly: enlargement of the liver.
Hepatosplenomegaly: enlargement of the spleen and liver.
Hereditary Coproporphyria (HCP): an acute porphyria due to a deficient activity of the enzyme, coproporphyrinogen oxidase.
Hereditary hemochromatosis: an autosomal recessive, genetic disorder, which leads to the accumulation of large amounts of iron in many organs, especially in the liver.
Heredity (or inheritance): refers to the passing on of traits from generation to generation.
Heterozygous: having two different forms (or alleles) of a particular gene. In other words, humans have 23 pairs of chromosomes, each chromosome containing a series of genes, and each gene being a specific DNA sequence. The two members of a pair include the same genes (termed alleles), but the two DNA sequences for a specific region may be the same or different. When they are different, the individual is said to be heterozygous for the region (gene). When they are identical, the term is homozygous.
HFE: a human gene that codes for a protein involved in iron regulation. A deficiency of the HFE protein causes hemochromatosis.
Hirsutism: growth of hair in excess of what is usual for a particular location.
HIV: human immunodeficiency virus.
Homozygous: having the same forms (or alleles) of a particular gene. In other words, humans have 23 pairs of chromosomes, each chromosome containing a series of genes, and each gene being a specific DNA sequence. The two members of a pair include the same genes (termed alleles), but the two DNA sequences for a specific region may be the same or different. When they are different, the individual is said to be heterozygous for the region (gene). When they are identical, the term is homozygous.
Hydroxychloroquine: an anti-malarial drug, also used to treat porphyria cutanea tarda.
Hydroxymethylbilane: an intermediate in the heme biosynthesis pathway.
Hydroxymethylbilane synthase (HMB-synthase): the third enzyme in the heme biosynthesis pathway; the half normal activity of this enzyme results in Acute Intermittent Porphyria (AIP).
Hyperpigmentation: skin darker than usual, as a result of excess melanin production. Small areas of hyperpigmentation are often seen in response to skin damage in porphyria.
Hypertrichosis: another term for Hirsutism.
Hypoglycemia: low blood sugar.
Hyponatremia: below-normal blood sodium; can occur in acute porphyria attacks, sometimes triggering a seizure.
Hypothalamus: a region of the brain that regulates basic processes including body temperature, hunger, thirst, fatigue, and circadian rhythm.