What is a characteristic feature of Thrombocytopenia Absent Radius?

Thrombocytopenia Absent Radius (TAR) syndrome is a rare genetic disorder that is characterized by the absence of the radius bones in the forearm, which can be bilateral. A defining feature of this condition is the bilateral absence of the radius while typically having present thumbs, though they may sometimes show structural abnormalities.

The correct characteristic aligns with the key clinical features of TAR syndrome. While the absence of radii is a primary focus, the presence of both thumbs is also a notable aspect, as many patients with TAR have normal or near-normal thumb development despite the forearm abnormalities. This distinction helps to identify TAR syndrome and differentiate it from other conditions that may present with similar limb malformations.

Other presentations, such as unilateral absence of a radius or complete absence of thumbs, do not align with the classic definition of TAR syndrome. Additionally, the statement regarding only skeletal malformations does not encompass the hematological aspects of the syndrome, such as thrombocytopenia, which is a hallmark feature. Overall, the presence of both thumbs despite bilateral absence of radii is integral to the understanding of this condition.