BACKGROUND: Type II (tyrosinase-positive) oculocutaneous albinism is an 
autosomal recessive disorder that has recently been mapped to chromosome segment 
15q11-q13. The frequency of this disorder is greatly increased in patients with 
Prader-Willi or Angelman syndrome, both of which involve deletions of chromosome 
15q. The P protein is a transmembrane polypeptide that may transport small 
molecules such as tyrosine, the precursor of melanin. The P gene is located in 
chromosome segment 15q11-q13.
METHODS: We studied the tyrosinase and P genes in three patients with type II 
oculocutaneous albinism, one of whom also had Prader-Willi syndrome, and in one 
patient with a milder syndrome known as autosomal recessive ocular albinism. 
Individual exons of these genes were amplified from the DNA of each patient by 
the polymerase chain reaction and screened for mutations by simultaneous 
analyses of single-stranded conformation polymorphisms and heteroduplexes and 
subsequent DNA sequencing.
RESULTS: Mutations of the P gene were identified in all four patients. These 
included one frame shift, three missense mutations that result in amino acid 
substitutions, and one mutation that affects RNA splicing. The patient with 
Prader-Willi syndrome plus albinism had a typical deletion of the paternal 
chromosome 15, rendering him hemizygous for a maternally inherited mutant allele 
of the P gene. The child with ocular albinism was heterozygous for two different 
mutations in the P gene.
CONCLUSIONS: Abnormalities of the P gene are associated with a wide range of 
clinical phenotypes, including type II oculocutaneous albinism, albinism 
associated with the Prader-Willi syndrome, and at least some cases of autosomal 
recessive ocular albinism.