RBM8A

Thrombocytopenia-absent radius syndrome

Mutations in the RBM8A gene cause thrombocytopenia-absent radius (TAR) syndrome. This disorder 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).

Most people with TAR syndrome have a mutation in one copy of the RBM8A gene and a deletion of genetic material from chromosome 1 that includes the other copy of the RBM8A gene in each cell. A small number of affected individuals have mutations in both copies of the RBM8A gene in each cell and do not have a deletion on chromosome 1. RBM8A gene mutations that cause TAR syndrome reduce the amount of RNA-binding motif protein 8A in cells. The deletions involved in TAR syndrome eliminate at least 200,000 DNA building blocks (200 kilobases, or 200 kb) from the long (q) arm of chromosome 1 in a region called 1q21.1. The deletion eliminates one copy of the RBM8A gene in each cell and the RNA-binding motif protein 8A that would have been produced from it.

People with either an RBM8A gene mutation and a chromosome 1 deletion or with two gene mutations have a decreased amount of RNA-binding motif protein 8A. This reduction is thought to cause problems in the development of certain tissues, but it is unknown how it causes the specific signs and symptoms of TAR syndrome. No cases have been reported in which a deletion that includes the RBM8A gene occurs on both copies of chromosome 1; studies indicate that the complete loss of RNA-binding motif protein 8A is not compatible with life.