Human digestive system digestive system is subject to a wide range of disorders many of which can be congenital. Mouth diseases can also be caused by pathogenic bacteria, viruses, fungi and as a side effect of some medications. Mouth diseases include tongue diseases and salivary gland diseases. A common gum disease in the mouth is gingivitis which is caused by bacteria in plaque. The most common viral infection of the mouth is gingivostomatitis caused by herpes simplex. A common fungal infection is candidiasis commonly known as "thrush" which affects the mucous membranes of the mouth. There are a number of esophageal diseases such
Human disease modifier gene and shifting from clinical reliance on epidemiological data to patient-specific genetic and biological data. Ultimately, developing therapeutics for human disease informed by an understanding of its molecular mechanisms is challenging. In the case where multi-gene interactions give rise to disease, a series of thorough methodological steps must be taken to determine these mechanisms. For the common case in which a major locus is causally associated with disease, but there exists considerable, unexplained phenotypic variation, this process of discovery typically begins with establishing heritability of the disease phenotype, and the reasonable likelihood that modifier genes contribute to the observed phenotypic variation.