People with Holt-Oram syndrome have abnormal development of bones in their upper limbs. At least one abnormality in the bones of the wrist (carpal bones) is present in affected individuals. Often, these wrist bone abnormalities can be detected only by X-ray. Individuals with Holt-Oram syndrome may have additional bone abnormalities including a missing thumb, a long thumb that looks like a finger, partial or complete absence of bones in the forearm, an underdeveloped bone of the upper arm, and abnormalities of the collar bone or shoulder blades.
To see some X-Rays: HERE
The disease is due to mutations in the transcription factor TBX5, which is important in the development of both the heart and upper limbs.
Note that Abnormalities may be unilateral or bilateral and asymmetric ( usually the left side is more affected).
About 75 percent of individuals with Holt-Oram syndrome have some cardiac abnormality. In most patients, the abnormality is either an atrial septal defect (ASD) or a ventricular septal defect (VSD), which varies in number, size, and location.