Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Congenital radio-ulnar synostosis ?
    ### Response:
    What causes congenital radio-ulnar synostosis? Congenital radio-ulnar synostosis is caused by abnormal development of the forearm bones in the fetal period, although the underlying cause of the developmental abnormality is not always known. The condition may be isolated (occur without other abnormalities) or it may be associated with various other skeletal, cardiac (heart), neurologic, or gastrointestinal abnormalities.
    