HPS is a double autosomal recessive disorder.  This means that a child has to inherit a faulty (mutated) gene from each parent) for them to have HPS.  When an individual has a single faulty HPS gene they are known as an unaffected carrier because they do not have symptoms of HPS but may pass the faulty gene on to their children.

When two unaffected carriers have a baby:

The diagram below illustrates the various combinations of genes that children may inherit from parents who are carriers.

So far mutations on 9 different genes have been found to cause HPS in humans.  In the laboratory ,mutations to 15 different genes have been found to cause HPS in lab mice.  It is believed that more genes will be identified in humans over the coming years as high through-put genetic sequencing techniques become more available.


The ‘true’ incidence of HPS is unknown but it is believed to occur across all nationalities and ethnic groups.  Estimates for the UK and Europe vary between 1 in 500,000 to 1 in 1 million.  The HPS Network believes that the ‘real’ incidence is higher because HPS is both under-diagnosed and frequently misdiagnosed as other forms of albinism.  Researchers believe HPS may also occur with greater frequency in Japan and in some small clusters in Switzerland.

However HPS is extremely prevalent in Puerto Rico.  In northwestern Puerto Rico one in 1,600 people in this region has HPS-1.  The highest incidence of HPS on the island is one in 1100.  One in 20 people in the northwestern part of Puerto Rico carry a faulty HPS-1 gene.   HPS-3 is also common on the island, primarily in the central region and one in 60 people on the island carry a faulty HPS-3 gene.  The HPS Network Inc. has a global membership of over 1000 including those from the UK.

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Diagram illustrating how mutated HPS genes can be passed from carrier parents to their children.  HPS, Hermansky-Pudlak Syndrome, is inherited in a double autosomal recessive manner. Picture of world atlas showing the locations of members of the HPS Network and also reported cases.

Genetics and prevalence of Hermansky-Pudlak Syndrome