Light micrograph of a section through human tissue showing ataxia-telangiectasia, a rare inherited multi-organ neurodegenerative disorder that affects the nervous system, immune system and other body systems. This disorder is characterised by progressive difficulty with coordinating movements (ataxia) beginning in early childhood, usually before the age of 5. It is caused by mutations in a gene on chromosome 11 known as the ATM gene, which is involved in cell cycle control. A person with this condition has an increased vulnerability to cancer and infection.