5q- Syndrome In a Child: Is This Acquired Diamond Blackfan Anemia (DBA)?

Diamond Blackfan anemia is a rare heritable red cell aplasia which usually presents in infancy but can also be diagnosed in childhood and even adulthood. Mutations or deletions in eleven ribosomal protein (RP) genes, resulting in protein haplo-insufficiency have been reported in about 54% of the patients. The 5q- syndrome is an acquired myelodysplastic syndrome (MDS) characterized by a similar erythroid failure. Another RP gene included in the 5q deleted region, RPS14, has been identified as a causal gene in 5q- MDS but has not been reported in DBA.

Array Comparative Genomic Hybridization has been used to identify large deletions in patients with DBA. This report demonstrates the use of Single Nucleotide Polymorphism (SNP) genotyping array hybridization to identify a patient, previously thought to have DBA, as having a 5q- deletion consistent with 5q- syndrome.

Seventy-five patient samples from the Diamond Blackfan Anemia Registry of North America, a patient database of now 608 patients designed to better understand the biology and epidemiology of DBA, underwent resequencing of 80 RP genes. Approximately 40% of the patients had no identifiable mutation. High resolution SNP array genotyping analysis was done on 23 probands from this cohort who did not have a mutation detected in either the resequencing project and/or the targeted sequencing efforts lead by Gazda and colleagues.

An acquired internal deletion on chromosome 5q involving RPS14 was identified in one patient with presumed DBA. The patient presented at 5 years 10 months of age with anemia noted on a routine blood count. The hemoglobin was 8.4 grams/dl, MCV 108.2 fL, and reticulocyte count 0.4%. The eADA was normal. The bone marrow showed decreased cellularity and megaloblastic changes in the erythroid series. There were adequate numbers of megakaryocytes with no hypolobulation. The cytogenetics performed at diagnosis in 1991 were reported as normal. The patient had no significant family history of anemia and was found to have no congenital physical anomalies. A diagnosis of non-classical DBA was presumed and the patient failed a trial of corticosteroids. At present the patient has marrow red cell aplasia and is on a chronic transfusion schedule. SNP array genotyping analysis identified mosaicism in two discrete regions covering ~17.7 Mb on 5q-, with an estimated 63.7% monosomy and 36.3% disomy in this region. The major region extends from 141.1M to 157.2M (hg18), including all of the 5q- syndrome commonly deleted region (CDR) at 5q33 though it excludes the 5q31 CDR associated with AML and more aggressive MDS as well as miR146a, a factor recently postulated to play a role in 5q- MDS. SNP array genotyping from purified peripheral blood populations indicated that lymphocytes were greater than 95% normal, while the myeloid cells were greater than 95% 5q-. CD34+ cells obtained from this patient showed a marked decrease in both myeloid and erythroid colony formation when compared with normal cells. Patient fibroblasts were normal and neither of the parents have any 5q anomalies by SNP array genotyping. Although the deletion was not identified in 1991 at the time of the diagnosis, the 46,XX,der(5)del(5)(q15q22)del(5)(q32q33) deletion was able to be detected on high resolution karyotyping in a post-SNP array genotyping marrow sample. Haploinsufficiency of RPS14 was confirmed by quantitative RT-PCR.

Patients with non-classical DBA may have unique acquired 5q deletions with RPS14 haploinsufficiency. A search for other acquired somatic mutations or deletions in patients with DBA, in particular non-classical cases, is underway. SNP array genotyping is an essential diagnostic tool in this search.

No relevant conflicts of interest to declare.