Chopin's disease and the cause of his death have since been a matter of discussion. His death certificate gave the cause as tuberculosis, and his physician, Jean Cruveilhier, was then the leading French authority on this disease. Other possibilities have been advanced including cystic fibrosis, cirrhosis and alpha 1-antitrypsin deficiency. However, the attribution of tuberculosis as principal cause of death has not been disproved. Permission for DNA testing, which could put the matter to rest, has been denied by the Polish government.