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 major locus, CFTR. In 1985, the gene was mapped by linkage analysis by Tsui et al., and in 1989, the gene was cloned by Riordan et al. When analyses of allelic variation in CFTR did not suffice to yield dependable genotype-phenotype correlations or explain the total phenotypic heterogeneity in CF, the existence of modifier loci was suspected and association studies, such as by Zielenski et al. in 1999, have identified and characterized these loci. Characterization of human disease modifier genes and oligogenic inheritance holds promise for understanding the abundance of phenotypic variation in human disease, which poses great challenge for