Identification and characterization of the first large deletion of the MYH9 gene associated with MYH9 disorders.

MYH9 disorders are autosomal dominant macrothrombocytopenias with leukocyte inclusion bodies. Single point mutations in the protein-coding sequence of the MYH9 gene are the most common cause. So far no large gene deletion/insertion and splicing defects have been reported. Conventional DNA sequencing of each MYH9-coding exon showed no abnormalities in a patient. Reverse transcription- polymerase chain reaction (PCR) amplification and sequencing of neutrophil mRNA identified an inframe deletion of exon 25. Further long-range PCR amplification of genomic DNA revealed a deletion of 1220 nucleotides including entire exon 25. Immunoblot analysis showed a small, abnormal protein in neutrophils but not in platelets. This is the first report of a large deletion of the MYH9 gene leading to the development of MYH9 disorders.