HPRP18 is a 342 amino acid protein that localizes to nuclear speckles and plays a role in the second step of pre-mRNA splicing. A member of the PRP18 family, PRPF18 contains seven WD repeats and exists as two alternatively spliced isoforms which are encoded by a gene located on human chromosome 10p13. Chromosome 10 contains over 800 genes and 135 million nucleotides. PTEN is an important tumor suppressor gene located on chromosome 10 and, when defective, causes a genetic predisposition to cancer development known as Cowden syndrome. Other chromosome 10 associated disorders include Cockayne syndrome, tetrahydrobiopterin deficiency and trisomy 10.