Extensive gene deletions in Japanese patients with Diamond-Blackfan anemia

Fifty percent of Diamond-Blackfan anemia (DBA) patients possess mutations in genes coding for ribosomal proteins (RPs). To identify new mutations, we investigated large deletions in the RP genes RPL5 , RPL11 , RPL35A , RPS7 , RPS10 , RPS17 , RPS19 , RPS24 , and RPS26 . We developed an easy method based on quantitative-PCR in which the threshold cycle correlates to gene copy number. Using this approach, we were able to diagnose 7 of 27 Japanese patients (25.9%) possessing mutations that were not detected by sequencing. Among these large deletions, similar results were obtained with 6 of 7 patients screened with a single nucleotide polymorphism array. We found an extensive intragenic deletion in RPS19 including exons 1 to 3. Other cases included a proband with an RPL5 deletion, 1 had an RPL35A deletion, 3 had RPS17 deletions, and 1 had an RPS19 deletion. In particular, the large deletions in the RPL5 and RPS17 alleles are novel. All patients with a large deletion had a growth retardation phenotype. Our data suggest that large deletions in RP genes comprise a sizable fraction of DBA cases in Japan. In addition, our novel approach may become a useful tool for screening gene copy numbers of known DBA genes.