Celiac disease is caused by an intolerance to gluten, a protein found in grains such as wheat, rye and oats (but not in rice or buckwheat). It is characterized by damage to the mucosa of the proximal small intestine, which results in poor absorption of most nutrients. It can also cause a wide range of maladies such as diarrhea, gas, and may contribute to mental depression in some people. Some forms of this disease are recessively inherited. The condition can be confirmed via a biopsy of the small intestine.