For families of children with rare diseases, the search for answers can be lonely, desperate and frustrating. Such is the case with pulmonary hypertension, or PH. Defined as high blood pressure in the lungs, PH forces the heart to work too hard. It has many causes, is incurable and can develop at any age. While it's difficult to calculate the number of cases of pediatric PH, particularly for those with genetic causes, its rarity does not diminish its devastating impact.