Clinical Guidance

Thrombocytopenia absent radius (TAR) syndrome is characterized by bilateral absence of the radii with the presence of both thumbs and thrombocytopenia that is generally transient. Additional manifestations can include cow's milk allergy and anomalies of the lower limbs, ribs, vertebrae, heart, and genitourinary system. To date, more than 150 individuals have been reported with a TAR-related RBM8A variant [, , , , , , , , , , , , , , , , , , , , , ]. The following description of the phenotypic features associated with TAR syndrome is based on these reports.

Diagnostic Criteria

Suggestive Findings

Thrombocytopenia absent radius (TAR) syndrome should be suspected in individuals with:

• Bilateral absence of the radii with the presence of both thumbs

• Thrombocytopenia, usually 50 platelets/nL (normal range: 150-400 platelets/nL)

Establishing the Diagnosis

The diagnosis of TAR syndrome is established in a proband with and a null heterozygous variant (most often a 500-kb deletion or 200-kb deletion including RBM8A at chromosome band 1q21.1) in a compound heterozygous state with a heterozygous RBM8A hypomorphic allele identified by molecular genetic testing .

Management Guidelines

Clinical practice guidelines for anesthesia and dental care in thrombocytopenia absent radius (TAR) syndrome have been published . Individuals with TAR syndrome have a high anesthetic risk. Considerations include potential difficulties with vascular and airway access, risk for bleeding due to altered platelet count and function, and potential congenital cardiac defects. All risks should be assessed carefully before surgery. Evaluations Following Initial Diagnosis To establish the extent of disease and needs in an individual diagnosed with TAR syndrome, the evaluations summarized (if not performed as part of the evaluation that led to the diagnosis) are recommended. Table 4. Recommended Evaluations Following Initial Diagnosis in Individuals with Thrombocytopenia Absent Radius Syndrome

Surveillance Guidelines

Table 6.

Recommended Surveillance for Individuals with Thrombocytopenia Absent Radius Syndrome

System/Concern | Evaluation | Frequency

Thrombocytopenia

| Platelet count | In those w/signs of bleeding tendency (bruising, petechiae)

Gastrointestinal