Gene-disease association with human IFNL locus polymorphisms extends beyond hepatitis C virus infections

Interferon (IFN) lambda (IFN-lambda or type III IFN) gene polymorphisms were discovered in the year 2009 to have a strong association with spontaneous and treatment-induced clearance of hepatitis C virus (HCV) infection in human hosts. This landmark discovery also brought renewed interest in type III IFN biology. After more than half a decade since this discovery, we now have reports that show that genetic association of IFNL gene polymorphisms in humans is not limited only to HCV infections but extends beyond, to include varied diseases such as non-alcoholic fatty liver disease, allergy and several other viral diseases including that caused by the human immunodeficiency virus. Notably, all these conditions have strong involvement of host innate immune responses. After the discovery of a deletion polymorphism that leads to the expression of a functional IFN-lambda 4 as the prime 'functional' variant, the relevance of other polymorphisms regulating the expression of IFN-lambda 3 is in doubt. Herein, I seek to critically address these issues and review the current literature to provide a framework to help further understanding of IFN-lambda biology.