The protein alpha-1-antitrypsin (AAT) is made in normally functioning liver cells. AAT plays an important role preventing damage, particularly to the liver and lungs, by an enzyme in white blood cells. This enzyme is released from white blood cells to fight infection, and AAT stops it from attacking normal tissues.
A mutation in the gene that codes for AAT can result in absent or abnormal protein that cannot control the white blood cell enzyme. This is Alpha-1 - antitrypsin deficiency (A1AD) which is a hereditary disease that may lead to hepatitis and cirrhosis. It is the most common genetic cause of liver disease in children. Adults are also affected and may also have lung problems such as emphysema as well as liver disease.
At the moment, treatment for A1AD includes use of antibiotics and generally leading a healthy life style i.e. not smoking and drinking alcohol but these are not permanent solutions and ultimately liver and lung transplants may be needed. Gene therapy may eventually provide a treatment for A1AD, but so far it has not proved possible to remove the mutant gene from human DNA.
Transgenic (or GM) sheep can help those A1AD sufferers who develop the lung disease emphysema. These animals have been genetically modified to produce milk that contains the human protein AAT. Supplies of AAT from this source are currently in clinical trials for A1AD and cystic fibrosis sufferers in many countries across the world.