Final answer:
Xeroderma pigmentosa is a hereditary disease that causes pigmented flat or circumscribed lesions. It is caused by a mutation in a gene affecting a single amino acid and is most commonly found in individuals of European origin.
Step-by-step explanation:
A hereditary disease that causes pigmented flat or circumscribed lesions is called xeroderma pigmentosa. Xeroderma pigmentosa is a condition in which thymine dimerization from exposure to UV light is not repaired, leading to skin lesions when exposed to sunlight. This disease is inherited from one or both parents and is caused by a mutation in a gene affecting a single amino acid. It is most commonly found in individuals of European origin.