Rare diseases, also known as rare diseases, have unknown causes and are mostly congenital or hereditary diseases, also known as orphan diseases. Rare diseases account for 0.65 per 1,000 of the total population and are difficult to cure but have a very low incidence. The most common rare diseases are the following: 1. albinism, a series of syndromes caused by genetic mutations that lead to defective melanogenesis. 2. acromegaly, a disease caused by excessive secretion of growth hormone due to hypothalamic and pituitary hyperplasia. 3. idiopathic pulmonary hypertension. 4. phenylketonuria. 5. mitochondrial disease.