Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Absence of Tibia ?
    ### Response:
    Absence of tibia is a rare birth defect that is characterized by deficiency of the tibia (the shinbone) with other bones of the lower leg relatively intact. The condition may affect one or both legs. Some cases are isolated birth defects, while others are associated with a variety of skeletal and other malformations.
    