Novel Kinase Found in Inherited
Thrombocytopenia

By Stephanie L. Perry, M.D.

Sometimes our journeys lead us to an unexpected outcome. In the Plenary Session, Abstract# 1608 entitled A Novel Kinase Mutated in Autosomal Dominant Thrombocytopenia on Human Chromosome 10, Dr. Manish Gandhi presented the intriguing discovery of a novel kinase designated “FLJ14813.”

From a previous study, Dr. Jonathan Drachman and colleagues published findings on a large family with autosomal dominant thrombocytopenia. Clinically, this form of inherited thrombocytopenia presents with moderate thrombocytopenia with mild to moderate bruising and minor bleeding history throughout life. Using genome-wide linkage analysis, Dr. Drachman and colleagues mapped this disorder to a single locus on the short arm of chromosome 10.

The next step was the task of identifying the specific gene involved in this inherited thrombocytopenia. Dr. Gandhi, Dr. Cummings, and Dr. Drachman again studied the large kindred and moderate thrombocytopenia was documented in 25 members out of 51. The researchers sequenced approximately 60,000 base pairs on chromosome 10 of two affected and one unaffected family member. This yielded the complete coding region and intron-exon boundaries of 36 genes. The investigators searched for single nucleotide polymorphisms (SNPs) and found five in the affected family members that were absent in controls. Additional family members were sequenced, and one mutation was eventually found to segregate with thrombocytopenia in the pedigree. This is a missense mutation in the human gene designated “FLJ14813,” which was found to be heterozygous in all 25 thrombocytopenic family members but not present in the unaffected individuals.

The function of FLJ14813 is unknown. From its sequence homology, however, it is known to contain two highly conserved kinase domains. In an attempt to discover the function of FLJ14813, the investigators made an antibody to FLJ14813 to develop a functional assay so that substrates for this kinase could be identified. They were able to show the expression of this gene in megakaryocytes (by RT-PCR), and megakaryocytic cell lines UT7-TPO, HEL and K562 (by Western blot).

To further investigate a potential role for this gene, experiments were performed in which the FLJ14813 kinase activity was measured before and after thrombopoietin (TPO)-stimulation of UT7- TPO cells. Thrombopoietin is known to cause growth in hematopoietic cells in the UT7-TPO cell line. It was discovered that the FLJ14813 kinase activity decreased by 30% after the cells were stimulated for 10 minutes, and these findings were confirmed.

From their work, the investigators concluded that mutations on the FLJ14813 gene cause a form of autosomal dominant thrombocytopenia. Commenting for the research team, Dr. Drachman states that “we are anxious to confirm our findings in additional families…” and to obtain further functional data. They are currently studying the possible role of FLJ14813 kinase in megakaryocytopoiesis.