I want to know what's the genetic cause for tar syndrome?

A bit complex: Thrombocytopena-Absent Radius may be caused by mutations in the RBM8A gene, or both a mutation and a deletion of the RMBA region..Absent Radius is associated with an absent thumb, except for this syndrome, so the diagnosis may be made clinically by noting TAR with thumb present. Milk allergy is very common, and can exacerbate low platelets http://www.ncbi.nlm.nih.gov/books/NBK23758/