What else is it called?
- albinism with haemorrhagic diathesis and pigmented reticuloendothelial cells
- delta storage pool disease
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What causes it?
HPS is caused by mutations (changes) in one of 10 genes (HPS1, AP3B1, HPS3, HPS4, HPS5, HPS6, DTNBP1, BLOC1S3, PLDN, and AP3D1). These genes provide instructions for making proteins used to make four separate protein complexes. These protein complexes are responsible for the formation and movement of a group of cell structures called lysosome-related organelles (LROs). LROs perform specific functions and are only found in certain types of cells. They are found in pigment-producing cells (melanocytes), platelets (blood clotting cells) and lung cells.
Mutations in the genes mentioned above, prevent the development of LROs or affect the functioning of these cell structures. HPS causes lack of pigmentation (colour) because the LROs within the melanocytes (cells producing melanin) cannot produce and transport the substance that gives skin, hair and eyes colour (melanin). When there are no LROs in the platelets, bleeding problems are caused because the platelets cannot stick together and form a blood clot. In some types of HPS the functioning of LROs in the lung cells are also affected which can cause pulmonary fibrosis (lung disease).
There are nine different types of HPS. These are distinguished by the signs and symptoms as well as the underlying genetic cause. Types 1 and 4 are the most severe forms of the condition. Types 1,2 and 4 are the only types that may cause pulmonary fibrosis (lung disease). Type 3,5 and 6 cause the mildest symptoms. There is little information about the signs, symptoms and severity of types 7,8 and 9.
How common is it?
Hermansky-Pudlak syndrome is a rare inherited disorder. It is estimated to affect 1 in 500,000 to 1,000,000 individuals worldwide. Type 1 of the condition is more common in Puerto Rico, specifically in the north western part of the island where an estimated 1 in 1,800 people are affected. Type 3 of the condition is more common in people from central Puerto Rico. Many other groups of individuals have been affected by the condition. Some affected regions that have been reported include India, Japan, the United Kingdom and Western Europe.
What are the signs and symptoms?
The first symptoms of HPS usually include:
- easy bruising
- bleeding gums
- nose bleeds
- excessive bleeding after surgery or accidents
Other classic symptoms of HPS include:
- lack of pigmentation (colour) in the skin, hair and eyes (oculocutaneous albinism)
- storage pool-deficient platelets (dysfunction of blood platelets causing prolonged bleeding)
- impaired eyesight
- inflammation of colon with bleeding (occurs in one-sixth of HPS patients)
The pigmentation (colour) of the skin, hair, and eyes of individuals with HPS can vary from very pale to almost normal colouring.
Eyesight in HPS patients is almost always impaired. It is common for individuals with this condition to have a vision of 20/200 or worse (legally blind).
The blood storage abnormality can cause excessive bleeding, particularly in women during their menstruation. Bleeding can become life-threatening. Aspirin is known the make the bleeding worse.
Individuals with type 1, 2 or 4 HPS can develop a lung disease (pulmonary fibrosis) which can be fatal.
How is it diagnosed?
A diagnosis of HPS usually starts with the presence of clinical features such as lack of pigmentation (colour) in the skin, hair and eyes. This can be followed by detecting dysfunction of blood platelets which can be confirmed with an electron microscope.
The diagnosis of HPS is confirmed through molecular genetic testing which will show mutations (changes) in the specific genes.
Can it be treated?
Treatment for HPS is aimed at the specific symptoms that come with the condition. Patients with excessive bleeding may need blood transfusions with normal blood platelets. Excessive bleeding during menstruation (menorrhagia) can be treated with oral contraceptives. HPS patients should avoid aspirin.
In HPS types 1,2 or 4 in the case of pulmonary fibrosis, patients may need a lung transplant.
Genetic counselling is recommended for HPS patients and their families.
Do my family need to be tested?
HPS is an inherited condition. Humans have chromosomes made up of DNA. Genes are pieces of DNA that carry the genetic information. Each chromosome may have several thousand genes. We inherit chromosomes from the egg of the mother and sperm of the father. The genes on those chromosomes carry the instructions that determine a person’s characteristics, which are a combination of the parents.
The pattern of inheritance of HPS is autosomal recessive. This means that carriers of the condition do not have the disorder because the other gene of this pair is working normally. Parents of children with HPS are carriers.
When both parents are carriers, the risk to the baby in each pregnancy is
- 25% chance (1 in 4) of developing the condition
- 50% chance (1 in 2) for the baby to be a carrier of the condition
- 25% chance (1 in 4) for the baby to have two working genes and neither have the condition nor be a carrier
Genetic counselling can be requested to get a full explanation.