Barrett esophagus, or Barrett metaplasia, describes the phenotypic change of normal esophageal squamous epithelium to a columnar and intestinal-type epithelium. This metaplastic change is important because patients with Barrett esophagus have an increased risk of esophageal adenocarcinoma. The main cause of Barrett metaplasia is gastroesophageal reflux (GER; 109350). The retrograde movement of acid and bile salts from the stomach into the esophagus in this disease causes prolonged injury to the esophageal epithelium and induces chronic esophagitis, which in turn is believed to trigger the pathologic changes (summary by Wong et al., 2005).

Esophageal cancer, particularly esophageal squamous cell carcinoma (ESCC), is one of the most common cancers worldwide. Both environmental and genetic risk factors play a role in the pathogenesis of the disorder. In Europe and North America, heavy smoking, alcohol consumption, and increased body mass index (BMI) are the main environmental risk factors. In contrast, the particularly high incidence of ESCC in some areas of China, central Asia, and southern Africa is associated with nutritional deficiencies, high intake of nitrosamine-rich or pickled vegetables, and low socioeconomic status; smoking, alcohol consumption, and BMI play a lesser role in these populations. There is a tendency for familial aggregation of ESCC in high-risk geographic areas, suggesting a genetic component to increased susceptibility. Gastric cardia adenocarcinoma is another common type of cancer in China that shows similarities to ESCC in terms of geographic distribution and environmental risk factors (summary by Wang et al., 2010 and Abnet et al., 2010). Genetic Heterogeneity of Susceptibility to Esophageal Cancer See a variant in the ADH1B gene (103720.0001) for discussion of a possible genetic association with protection against squamous cell aerodigestive tract cancer, including esophageal cancer, in alcohol drinkers. See a variant in the ALDH2 gene (100650.0001) for discussion of a possible genetic association with increased risk for esophageal cancer in alcohol drinkers due to interaction between variants in the ADH1B and ALDH2 genes. See the S100A14 gene (607986) on chromosome 1q21 for a discussion of a possible association between variation in that gene and susceptibility to esophageal squamous cell carcinoma among smokers. Genetic Heterogeneity of Somatic Mutations in Esophageal Cancer Somatic mutations in several different genes have been found in esophageal cancer tissue. These genes include TP53 (191170), CDKN2A (600160), DEC1 (604767), DCC (120470), DLEC1 (604050), TGFBR2 (190182), LZTS1 (606551), RNF6 (604242), WWOX (605131), APC (611731), and RUNX3 (600210).

Palmoplantar keratoderma (PPK) is a complex group of hereditary syndromes that have been classified into diffuse, punctate, and focal forms according to the pattern of hyperkeratosis on the palms and soles (Lucker et al., 1994). For a discussion of phenotypic and genetic heterogeneity of palmoplantar keratoderma, see epidermolytic PPK (144200).