PLEKHJ1 (pleckstrin homology domain containing, family J member 1), also known as GNRPX (guanine nucleotide-releasing protein x), is a 149 amino acid phosphoprotein that contains one PH (pleckstrin homology) domain and is expressed in testis and liver. The gene that encodes PLEKHJ1 maps to human chromosome 19, which consists of approximately 63 million bases and makes up over 2% of human genomic DNA. Chromosome 19 contains the greatest gene density of the human chromosomes and is the genetic home for a number of immunoglobulin superfamily members, including killer cell and leukocyte Ig-like receptors, ICAMs, the CEACAM and PSG families, and Fcα receptors. Key genes for eye color and hair color also map to chromosome 19. Peutz-Jeghers syndrome, spinocerebellar ataxia type 6, the stroke disorder CADASIL, hypercholesterolemia and insulin-dependent diabetes are also linked to chromosome 19.