Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Anonychia congenita ?
    ### Response:
    Anonychia congenita is an extremely rare nail disorder characterized by the complete absence (anonychia) or abnormally developed  fingernails and toenails. Affected individuals usually do not have hair, teeth, or bone abnormalities. Signs and symptoms are variable, even among affected members of the same family.
    