NAP5 (Nck-associated protein 5), also known as peripheral clock protein, NCKAP5 or ERIH, is a 1,909 amino acid nuclear protein that is expressed in fetal and adult brain, leukocytes and fetal fibroblasts. Containing pro-rich sequences, NAP5 interacts with the adapter protein Nck via the SH3-containing region. Existing as four alternatively spliced isoforms, the gene encoding NAP5 maps to human chromosome 2q21.2 and mouse chromosome 1 E3. Human chromosome 2, the second largest human chromosome, consists of 237 million bases, encodes over 1,400 genes and makes up approximately 8% of the human genome. Harlequin icthyosis, a rare and morbid skin deformity, is associated with mutations in the ABCA12 gene present on chromosome 2. The lipid metabolic disorder sitosterolemia is associated with ABCG5 and ABCG8. An extremely rare recessive genetic disorder, Alstr syndrome, is due to mutations in the ALMS1 gene.