Below is an instruction from Human. Write a response.
    ### Instruction:
    How many people are affected by pulmonary veno-occlusive disease ?
    ### Response:
    The exact prevalence of PVOD is unknown. Many cases are likely misdiagnosed as idiopathic pulmonary arterial hypertension, which is increased blood pressure in the pulmonary arteries without a known cause. Research suggests that 5 to 25 percent of people diagnosed with idiopathic pulmonary arterial hypertension have PVOD.
    