Thrombocytopenia-Absent Radius Syndrome

Abstract

Typical clinical features of thrombocytopenia-absent radius (TAR) syndrome are bilateral absence or hypoplasia of the radius in the presence of both thumbs and a reduction in the number of platelets (thrombocytopenia; <50 platelets/nl). Additional skeletal features include shortening and, less commonly, aplasia of the ulna and/or humerus. In the latter situation, the five-fingered hand arises from the shoulder. The hands may show limited extension of the fingers and radial deviation. There may be hypoplasia of the carpal and phalangeal bones. The musculature of the hands, arms, and shoulders can be hypoplastic. The lower limbs are frequently involved (~50 %) but to a lesser extent than the upper limbs. Dislocation of the hips and subluxation of the knees resulting in coxa vara are common. Extraskeletal manifestations comprise cardiac abnormalities, such as tetralogy of Fallot and atrial and ventricular septal defects (15–25 %), and abnormalities of the genitourinary tract (renal anomalies and agenesis of the uterus, cervix, and upper part of the vagina). Craniofacial features include brachycephaly, micrognathia, strabismus, ptosis, and a small, upturned nose. Cow’s milk allergy or intolerance appears to be relatively common among patients with TAR syndrome and may provoke eosinophilia.