Holt-Oram syndrome, also called heart-hand syndrome, is an inherited disorder that causes abnormalities of the upper limbs and heart. About one in 100,000 people are affected. Affected individuals may have malformed thumbs and/or arms on one or both sides. About 70% have congenital heart defects. Holt-Oram is inherited in an autosommal dominant fashion, although most are due to new mutations. This disorder is caused by mutations in the TBX5 gene on chromosome 12q.