The two patients with HPS were homozygous for nonsense mutation (T/T) for the c.541C>T (rs119471022) in the HPS4 gene, which is mapped to human chromosome 22q12.1.
We have identified and found mutations of the human le homolog, HPS4, in a number of non-Puerto Rican individuals with HPS, establishing HPS4 as an important HPS locus in humans.