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 most obviously important to understanding the roles of modifier loci in causing human genetic disease is identifying them. The size and complexity of the human genome make this a challenging task. Methods of identifying modifier loci can be categorized into three major approaches: genotype-phenotype correlations, linkage and association studies, and experimental phenotypic analyses in animal models. Commonly, speculation of the responsibility of modifier loci for phenotypic variation of human disease arises from observations of genotype-phenotype correlations that deviate from simple, Mendelian inheritance of mutations at a single locus. Bardet-Biedl syndrome (BBS) provides one such example. BBS is a genetically-heterogeneous disorder