Thrombocytopenia-absent radius (TAR) syndrome is characterized by the absence of a bone called the radius in each forearm and a shortage (deficiency) of blood cells involved in clotting (platelets). This platelet deficiency (thrombocytopenia) usually appears during infancy and becomes less severe over time; in some cases the platelet levels become normal.

Mutations in the RBM8A gene cause TAR syndrome. The RBM8A gene provides instructions for making a protein called RNA-binding motif protein 8A. This protein is believed to be involved in several important cellular functions involving the production of other proteins.

TAR syndrome is a rare disorder, affecting fewer than 1 in 100,000 newborns.

TAR syndrome is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell are altered. In this disorder, either both copies of the RBM8A gene in each cell have mutations or, more commonly, one copy of the gene has a mutation and the other is lost as part of a deleted segment on chromosome 1. The affected individual usually inherits an RBM8A gene mutation from one parent. In about 75 percent of cases, the affected person inherits a copy of chromosome 1 with the 200-kb deletion from the other parent. In the remaining cases, the deletion occurs during the formation of reproductive cells (eggs and sperm) or in early fetal development. Although parents of an individual with TAR syndrome can carry an RBM8A gene mutation or a 200-kb deletion, they typically do not show signs and symptoms of the condition.

Published Date: February 01, 2017
Published By: National Institutes of Health