The DEFB4 gene encodes one of the beta-defensin genes located in a cluster within the chromosome 8p23.1 region. Genes in this cluster encode proteins with a variety of antimicrobial functions.
Copy number variation (CNV) of medical significance has been reported for the beta-defensin cluster of genes. It appears as if:
- Most (healthy) individuals have a total of 4 copies of the beta-defensin cluster [PMID 16909382]
- Individuals with 3 or less copies of these genes are at 3x higher risk of developing Crohn's disease [PMID 16909382]; the good news is that individuals with 2 copies are also at 0.3x lowered risk for psoriasis [PMID 18059266]
- Individuals with 5 or more copies of these genes are at higher risk for psoriasis; the estimate for increased risk can be calculated as 0.34x more (starting with 1.00 for 4 copies) per extra copy.[PMID 18059266]