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  • Defect:  an abnormality.
  • Deficiency: a lower amount of enzyme compound that is necessary for normal function.
  • Delta-aminolevulinic acid: see Aminolevulinic acid.
  • Dialysis: 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.
  • Disease: deviation from a normal state of physical or mental health caused by the body’s response to the genetic defects, the environment, and/or infectious substances.
  • Disorder: an abnormal physical or mental condition.
  • DNA (deoxyribonucleic acid): a molecule that contains the genetic instructions used in the development and functioning of living organisms, including some viruses.
  • Dominant inheritance: type of inheritance pattern wherein only one affected parent is needed to pass on the trait to their children. Each child of a parent who carries the trait has a 50% chance of inheriting the trait.
  • Dual porphyrias: the presence of more than one type of porphyria in an individual. This is known but is rare.