Hermansky-Pudlak syndrome (HPS)

A genetic disorder characterized by albinism (with lack of pigment in the skin or eye), bruising and prolonged bleeding (due to defective blood platelets), and fibrosis of the lungs. There is occasionally also inflammatory bowel disease and impaired kidney function. All HPS patients suffer from varying degrees of albinism. The lack of pigment in the eye impairs their vision and often leads to involuntary rhythmic eye movements called nystagmus. The most serious health problems in HPS are the tendency to bruise easily and bleed and the progressive deterioration in lung function. The reason HPS patients bleed too easily is that their blood platelets are deficient in so-called dense bodies. These subcellular organelles release their contents to make other platelets stick together and form a clot. Without dense bodies, the time needed for a clot to form is abnormally slow. Women with HPS may therefore need medical intervention during their menstrual cycles or at childbirth. HPS patients are advised to avoid blood anticoagulants such as aspirin. Drugs are needed to prevent excessive bleeding during dental extractions and other surgical procedures. Inflammatory bowel disease with the onset of symptoms between 10 and 30 years of age can complicate HPS and usually responds poorly to therapy. The lung problems in HPS begin with restrictive disease and then progress inexorably to death, usually in the fourth or fifth decade. HPS patients have a biochemical storage disorder. They accumulate a fatty product called ceroid lipofuscin. This causes inflammation in tissues such the lungs. Prolonged inflammation leads to fibrosis, which in the case of the lung impairs its ability both to expel air and to exchange carbon dioxide for oxygen. HPS is inherited as an autosomal recessive condition affecting males and females. Both parents carry an HPS gene (along with a normal gene) and the risk to each of their children is 1 in 4 to receive both of their HPS genes and have the disease. HPS occurs in many countries. It is especially common in certain areas in the Swiss Alps and Puerto Rico. In NW Puerto Rico, 1 in every 1800 individuals is affected with HPS and 1 in 21 persons carries the HPS gene. The HPS is genetically heterogenous. It is not a single genetic entity. Mutations in different genes on different chromosomes are now known to lead to HPS. Gene loci for HPS have been identified on chromosomes 3, 5 and 10. Puerto Ricans with HPS have been found to have mutations in the HPS1 gene and, less often, in the HPS3 gene. Only half of individuals with HPS not from Puerto Rico have mutations in HPS1 and very few do in HPS3; and a number have mutations in another locus, HPS4.